Sangean ATS-909 external antenna impedance??
Lostgallifreyan
is?
I searched for days for documentation on that radio and found plenty, mods,
schematics, service manuals, reviews, but no straight word on the impedance
of that input! (Not even in the service manual specs). The only reference I
found was a from a guy on a 7-page set of ham reviews, and all he said was
that it was a mystery!
Maybe the only way to know is to start from the schematic but I don't know
how, but here's the best schematic I could find:
http://eric.horsemensociety.info/TECH/images/ATS909_Schematic_A.gif
(Antenna input is near top right).
(Link appears to be dead, 403, forbidden. I'm sure it worked last week..)
What I really want to know is whether the ATS-909 will work ok with a
long(ish) wire outside feeding a 50 ohm coax via a 9:1 transformer, or if
that would cause more bother than connecting a wire directly to it and
putting up with local noise picked up from nearby buildings.
Dave
just hook it up with the coax even without the transformer and it
should be fine.
Gaius
> Does anyone know what the Sangean ATS-909's external antenna input impedance
> is?
> What I really want to know is whether the ATS-909 will work ok with a
> long(ish) wire outside feeding a 50 ohm coax via a 9:1 transformer, or if
> that would cause more bother than connecting a wire directly to it and
> putting up with local noise picked up from nearby buildings.
There's a 1K0 pot across the input which is used as a cheap and cheerful
RF gain control. So i'd assume about 1K. You wouldn't have a problem
with the wire attached direct, but you'll get lots of front end
intermod, as it's wide open - just a low pass filter (presumably 30MHz
cut off)before the RF amp. A bit of preselection is pretty necessary for
an external wire of any size.
Lostgallifreyan
a421c0...@m25g2000yqc.googlegroups.com:
Really? Wouldn't that be 'matching' a fairly high impedance in the wire to
the low 50 ohm coax, then risking further loss in unknown input impedance
mismatch? I like the idea though, if I thought it would be that easy I might
have tried it. :) If it's really ok I'll do it. I haven't got scope for a
really long wire so I do need to try to minimise losses, I imagine..
Ralph Mowery
"Lostgallifreyan" <no-...@nowhere.net> wrote in message
news:Xns9CE69B09D13...@216.196.109.145...
Who cares what the impedance is for that radio. Unless you plan on putting
up an antenna for one very narrow band of frequencies, the impedance of the
system will be all over the place. YOu can probably run coax to the antenna
and never have any problems.
Lostgallifreyan
news:4b2d04c1$0$2488$db0f...@news.zen.co.uk:
Front end intermod? Do you mean pickup from local active gain stages or other
RF subcircuits in the receiver being picked back up by the wire antenna and
makign sum/difference signals or similar effects?
Also, I see that pot now, (and noticed that it also affects the telescopic
inbuilt antenna's pickup on SW (not FM as far as I know)), but I also see a
lot of other parts associated with that part of the circuit. I don't know
enough to be sure but it seems they might complicate the picture. If not, I
don't know why the impedance seems to be a mystery. If it were well
established I know my searches would found it so in triplicate by now...
Lostgallifreyan
news:1smdnSTij4Ock7DW...@earthlink.com:
Ok, so that's two people saying that could work, and sure, I won't be relying
on a single narrow range, I want to see what's out there and detectable. I
might want to limit peaks and troughs in sensitivity by using a 9:1
transformer though, as I read several times that it is a useful way to do
that for general SW listening via a long wire. That alone means I probably DO
need to care about impedance matching.
Gaius
I've just found a schematic JPG - 475Kb. It claims to be a "RK777", but
I think that's one of the 909's aliases. I can send it - mail me at john
at aultmore dot net.
IanT
You need an impedance matching device otherwise incorrectly called
"antenna tuning unit". It doesn't tune the antenna, it only matches the
impedance
for a given frequency. The main loss will be with the aerial NOT being
resonant at your chosen frequency.
The only way you are going to find out is try what people have suggested,
then compare the results for yourself.
Bob
<no-...@nowhere.net> wrote:
>Does anyone know what the Sangean ATS-909's external antenna input impedance
>is?
The Sangean external antenna input is a 2.1mm jack which would
acommodate a high impedance long wire, as per the instructions:
"ANT-60 PORTABLE SW ANTENNA
Included with the ATS-909 is the Sangean ANT-60 Portable SW Antenna.
The antenna is plugged into
jack (26) labeled EXT AM ANT. When fully extended this antenna should
improve SW reception. For
maximum performance this antenna should be placed as high as possible
above the ground and in an
unobstructed area if possible."
Your idea of attaching the antenna via 50 ohm coax would probably be
below the impedance range of the jack, tho' I'm not sure you would
really hear much difference.
If the Sangean external antenna input were designed for 50 ohm coax,
it would probably have a coax jack, not the 2.1 mm jack.
bob
k5qwg
Ian Jackson
<rmil...@satx.rr.com> writes
>
>If the Sangean external antenna input were designed for 50 ohm coax,
>it would probably have a coax jack, not the 2.1 mm jack.
>
The 'type' of connector - especially on something like a small portable
radio - is absolutely NO guide to the input impedance (which, actually
could be almost anything). It's often determined by the need to keep it
small. I have a small VHF/UHF TV set which use a 3.5mm audio jack.
--
Ian
Lostgallifreyan
news:io9ri5hoppjnarnai...@4ax.com:
> The Sangean external antenna input is a 2.1mm jack which would
> acommodate a high impedance long wire, as per the instructions:
>
3.5mm, not 2.1mm
> "ANT-60 PORTABLE SW ANTENNA
> Included with the ATS-909 is the Sangean ANT-60 Portable SW Antenna.
> The antenna is plugged into
> jack (26) labeled EXT AM ANT. When fully extended this antenna should
> improve SW reception. For
> maximum performance this antenna should be placed as high as possible
> above the ground and in an
> unobstructed area if possible."
>
I know that, it was the first thing I found, but it doesn't answer any
questions about impedance, especially if the radio you buy is second hand and
doesn't have the antenna wire with it.
> Your idea of attaching the antenna via 50 ohm coax would probably be
> below the impedance range of the jack, tho' I'm not sure you would
> really hear much difference.
>
> If the Sangean external antenna input were designed for 50 ohm coax,
> it would probably have a coax jack, not the 2.1 mm jack.
>
Agreed, which is why I don't assume it's 50 ohms, and I start looking for
answers. I think you're likely right that it might not make enough difference
to worry about though. If using coax can get the SNR higher I'm in business
so long as the signal is strong enough for the input's gain to use.
Lostgallifreyan
news:4b2d155e$0$2525$da0f...@news.zen.co.uk:
Thanks, but I'm ok, I got a schematic.. It just appears that those links
became forbidden access in the week or so since I found them. Might even be a
local error, thogh as I no longer do HTML or User-Agent filtering or similar
things I can't see what the cause might be.
Lostgallifreyan
news:hgj676$b0r$1...@news.eternal-september.org:
>> Ok, so that's two people saying that could work, and sure, I won't be
>> relying
>> on a single narrow range, I want to see what's out there and
>> detectable. I might want to limit peaks and troughs in sensitivity by
>> using a 9:1 transformer though, as I read several times that it is a
>> useful way to do that for general SW listening via a long wire. That
>> alone means I probably DO
>> need to care about impedance matching.
>
> You need an impedance matching device otherwise incorrectly called
> "antenna tuning unit". It doesn't tune the antenna, it only matches the
> impedance
> for a given frequency. The main loss will be with the aerial NOT being
> resonant at your chosen frequency.
> The only way you are going to find out is try what people have
> suggested, then compare the results for yourself.
>
Thanks, that could be useful. I've heard of them, wasn't sure if I'd need
something beyond a means to reduce peaks and troughs in resonance or
sensitivity across bands while trying to match impedance though. I read some
old posts by John Doty (archived on web sites) that suggested that a single
device could be set and placed at the end of the antenna wire and grounded
there too, and then weatherproofed and ignored. :) It's an attractive idea.
amdx
Hey Lost,
This page has lots of good info,
http://www.hard-core-dx.com/nordicdx/antenna/feed/magbalun.html
Sounds like the N8KDV Transformer would work for you, but you
still don't know the input impedance of your radio. You could try
getting that info from Sangean.
The problem you have is whatever antenna you have the impedance changes
with frequency. If you find a band that interests you, build an antenna for
that band.
Here's another that shows how impedance changes with frequency, it's put
in
mismatch loss rather than resistance and reactance, but it gives the general
idea.
www.iw5edi.com/ham-radio/?swl-longwires,47
Mike
amdx
about the Sangean.
Mike
Bob
You might shoot an email to tech at C.Crane Co. -- a lot of their
branded radios are actually customized Sangeans...they might be able
to tell you the most effective antenna and/or the impedance of the
thing.
bob
k5qwg
Lostgallifreyan
news:g4isi5ds5lkfl5q21...@4ax.com:
> You might shoot an email to tech at C.Crane Co. -- a lot of their
> branded radios are actually customized Sangeans...they might be able
> to tell you the most effective antenna and/or the impedance of the
> thing.
>
> bob
> k5qwg
>
Nice, I saw their page, didn't check that far though, and it is worth a try.
Lostgallifreyan
news:b72de$4b2e4527$18ec6dd7$90...@KNOLOGY.NET:
> www.iw5edi.com/ham-radio/?swl-longwires,47
Oh yeah.. :) Saw that one. That was what I had in mind. It irons the bumps
out. That guy mentions John Doty, his page was one of many I found while
looking for John Doty's DIY transformer plans. (Still not found those).
The way I see it (hopefully this is right) is that those deep level
variations really DO need smoothing out as described there, because they
represent signal loss greater than is likely to be caused by other errors
like basic mismatches, and possible overload at peaks as Europe has many
strong SW stations. Again, if I can use coax to increase SNR by reducing
noise out of nearby buildings, it reduces the problem to one of loss/gain.
As Anthony Alouitius StJohn Hancock pronounced: "Stone me, you've got to have
something to start with!". Not that I'd trust his judgement as a radio ham.
:)
That's my plan for the other end of the wire though, the question is whether
I'll have trouble at the ATS-909 radio end if I use it. Though I guess the
antenna matcher (misnamed 'tuner' as IanT mentioned in his post) can help,
and probably further assist the business.
I'll probably try longwire straight to coax first just to see what results,
then an earth rod to ground the coax far end, and then the 9:1 transformer,
before considering the more complex adjustable impedance matcher though. Got
other problems like money and dodgy neighbour problems to solve first too,
which is why I'm saying more than doing right now (and gathering info). Once
I start doing, I need to minimise the actions so I don't have more than
reception issues to worry about.
amdx
> "amdx" <am...@knology.net> wrote in
> news:b72de$4b2e4527$18ec6dd7$90...@KNOLOGY.NET:
>
>> www.iw5edi.com/ham-radio/?swl-longwires,47
>
> Oh yeah.. :) Saw that one. That was what I had in mind. It irons the bumps
> out. That guy mentions John Doty, his page was one of many I found while
> looking for John Doty's DIY transformer plans. (Still not found those).
>
> The way I see it (hopefully this is right) is that those deep level
> variations really DO need smoothing out as described there, because they
> represent signal loss greater than is likely to be caused by other errors
> like basic mismatches, and possible overload at peaks as Europe has many
> strong SW stations. Again, if I can use coax to increase SNR by reducing
> noise out of nearby buildings, it reduces the problem to one of loss/gain.
>
> As Anthony Alouitius StJohn Hancock pronounced: "Stone me, you've got to
> have
> something to start with!". Not that I'd trust his judgement as a radio
> ham.
> :)
>
> That's my plan for the other end of the wire though, the question is
> whether
> I'll have trouble at the ATS-909 radio end if I use it. Though I guess the
> antenna matcher (misnamed 'tuner' as IanT mentioned in his post) can help,
> and probably further assist the business.
>
Well most tuner/antenna matcher are designed to take the impedance that
the
antenna cable presents and transformer it to 50 ohms. Your problem is the
Sangean is probably not 50 ohms. So to do it all right, you need to know the
antenna impedance at the frequency of interest., transform that to 50 ohms,
send it down the 50 ohm coax then transform it up (guess) to 600 ohms for
the Sangean.
Here's a good plot of resistance and reactance vs frequency.
http://thebellringers.blogspot.com/2009/04/plot-of-impedance-vs-frequency.html
The top graph, (Blue Line) is resistance and the (Red Line) is reactance
plotted from
1Mhz to 30 Mhz. As you can see it swings wildly. One antenna won't do it
all.
> I'll probably try longwire straight to coax first just to see what
> results,
> then an earth rod to ground the coax far end, and then the 9:1
> transformer,
> before considering the more complex adjustable impedance matcher though.
> Got
> other problems like money and dodgy neighbour problems to solve first too,
> which is why I'm saying more than doing right now (and gathering info).
> Once
> I start doing, I need to minimise the actions so I don't have more than
> reception issues to worry about.
You might find this useful, to stay out of neighbor problems.
http://www.kongsfjord.no/dl/Antennas/The%20Best%20Small%20Antennas%20For%20MW,%20LW,%20And%20SW%20rev%202.pdf
The start page for that link is here;
http://www.kongsfjord.no/dl/dl.htm
Mike
Lostgallifreyan
news:b7cca$4b2e631f$18ec6dd7$20...@KNOLOGY.NET:
> Here's a good plot of resistance and reactance vs frequency.
> http://thebellringers.blogspot.com/2009/04/plot-of-impedance-vs-frequency
> .html The top graph, (Blue Line) is resistance and the (Red Line) is
> reactance plotted from
> 1Mhz to 30 Mhz. As you can see it swings wildly. One antenna won't do it
> all.
>
It's going to have to do the best it can. :) though I might find scope to try
a few variants, more than one shorter wire, for example. Just got to reduce
trial and error because that's what might cause neighbourly upset.
>
> You might find this useful, to stay out of neighbor problems.
> http://www.kongsfjord.no/dl/Antennas/The%20Best%20Small%20Antennas%20For%
> 20MW,%20LW,%20And%20SW%20rev%202.pdf
>
That I like. I also saw your earlier link before but went back to reread what
he (the Florentian Ham) said about antennas for apartments (That page looks
like a CSS disaster but the advice is good), and especially the how-it-works
paragraphs on longwire matching.
From what I can tell, it might not need a long or large antenna at all, so
long as it doesn't have high resonance, sharp bandwidth, or noise. I imagined
that if a small antenna (perhaps with capacitative or inductive loading)
could cover the wide range from 1.7 MHz to 30 MHz without much modification
then so long as common mode signals were strongly reduced, and the other
problems solved, extra gain could be used between the coax and receiver, and
that PDF shows a way to do it. I guess loading with deliberately higher
resistance involved to damp resonances will be ok with a small antenna and a
preamp if I can mount the antenna near a remote ground and get the coax
right. I'll try to avoid complexity I find hard to grasp though.
I might also more easily find 30 feet straight upwards than in any other
direction... Already got an FM 1/4 wave dipole out there doing just that.
Lostgallifreyan
news:b7cca$4b2e631f$18ec6dd7$20...@KNOLOGY.NET:
> Well most tuner/antenna matcher are designed to take the impedance that
> the
> antenna cable presents and transformer it to 50 ohms. Your problem is the
> Sangean is probably not 50 ohms.
Ah, but in reverse? :) I don't know if this is good thinking, but if the coax
IS 50 ohms, could I not put the 50 ohm connection onto the coax and tweak the
other end (on the input instead of the coax) impedance by watching the signal
strength meter on the receiver?
(Might be undeed according to posts people made earlier that suggest that
losses here might matter less than what happens on the longwire end of the
coax).
Lostgallifreyan
news:Xns9CE7B9F9550...@216.196.109.145:
> undeed
Un-needed. Some typos shall not pass.
Dave Platt
Lostgallifreyan <no-...@nowhere.net> wrote:
>The way I see it (hopefully this is right) is that those deep level
>variations really DO need smoothing out as described there, because they
>represent signal loss greater than is likely to be caused by other errors
>like basic mismatches, and possible overload at peaks as Europe has many
>strong SW stations. Again, if I can use coax to increase SNR by reducing
>noise out of nearby buildings, it reduces the problem to one of loss/gain.
Looking at it from the opposite angle, though: it's fairly common in
the HF bands for the signal level isn't the limiting factor in your
reception. Even an inefficiently-matched antenna can deliver enough
signal to overcome the self-noise of the front-end circuitry in your
receiver.
What limits your ability to receive, under these conditions, is band
noise and other spurious signals, which "drown out" the desired
signal. Improving the antenna matching wil have little or no benefit
in dealing with external noise. Neither will a preamp.
Now, using coax as a way of excluding some of the close-in interferers
isn't a bad idea at all. What you might want to consider doing, is
adding an active buffer at the longwire-to-coax feedpoint...
basically, a low-gain preamp (a few dB) designed to drive a 50-ohm
load efficiently and to overcome the (slight) signal losses in the
coax. Some people seem to favor the grounded-base or grounded-gate
broadband amplifier, as it has a modest gain, can be quite stable, and
has a good resistance to strong-signal overload. You could use a DC
inserter/block system to feed 9-12 volts up the same coax which
carries the signal down.
If you're really concerned about matching the resulting coax-carried
signal to your radio's antenna input, you could wind a fixed-ratio
broadband transformer with the correct impedance ratio.
--
Dave Platt <dpl...@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
Lostgallifreyan
> What limits your ability to receive, under these conditions, is band
> noise and other spurious signals, which "drown out" the desired
> signal. Improving the antenna matching wil have little or no benefit
> in dealing with external noise. Neither will a preamp.
>
Point taken, at least with the matching vs noise. Others have said it won't
matter much and I see why. preamp might be another issue though, especially
in light of 'amdx's post:
"http://www.kongsfjord.no/dl/Antennas/The%20Best%20Small%20Antennas%20For%20M
W,%20LW,%20And%20SW%20rev%202.pdf
The start page for that link is here;
http://www.kongsfjord.no/dl/dl.htm"
> Now, using coax as a way of excluding some of the close-in interferers
> isn't a bad idea at all. What you might want to consider doing, is
> adding an active buffer at the longwire-to-coax feedpoint...
> basically, a low-gain preamp (a few dB) designed to drive a 50-ohm
> load efficiently and to overcome the (slight) signal losses in the
> coax. Some people seem to favor the grounded-base or grounded-gate
> broadband amplifier, as it has a modest gain, can be quite stable, and
> has a good resistance to strong-signal overload. You could use a DC
> inserter/block system to feed 9-12 volts up the same coax which
> carries the signal down.
>
This is a good idea, though maybe the one I learned and reposted might do
better, it has a very attractive aspect, as it drives a simple speaker wire.
That stuff is cheap, (even the heavy stuff is cheap and durable, I use it
already for solar power..), and effectively forms a very low loss balanced
current loop that is isolated entirely from any current path anywhere else. I
wouldn't even have to bury the feed line, I could likely just run it along
the guide wire in a nearby chainlink fence or whatever is convenient because
it will very effectively reject common mode noise. It might still benefit
from a preamp current driver at the far end but as it uses a low impedance
input at the near end to take care of common mode noise it should be fine,
and a lot easier to get power to. :)
> If you're really concerned about matching the resulting coax-carried
> signal to your radio's antenna input, you could wind a fixed-ratio
> broadband transformer with the correct impedance ratio.
>
Might try that, though more as an effort to extend learning than any need.
Right now I'm really glad I asked here because these answers are good, and I
now seem to have a better idea (the vertical long whip and balanced feed and
Norton preamp scheme) than the longwire-and-balun-and-coax I'd originally
intended. I haven't yet verified the new idea but it appears to be from
someone who has demonstrated capability among a group of radio hams, and it
certainly fits with what I know without contraindications, and it would be
much easier to arrange safely and discreetly than any other scheme I've seen.
The author even states permanently retiring his longwires and inverted L's
and so forth in favour of a phased array of two of the vertical whip. I
haven't got the 60 feet of space for the two he specifies, but I think I'll
do ok with one.
amdx
> "amdx" <am...@knology.net> wrote in
> news:b7cca$4b2e631f$18ec6dd7$20...@KNOLOGY.NET:
>
>> Well most tuner/antenna matcher are designed to take the impedance that
>> the
>> antenna cable presents and transformer it to 50 ohms. Your problem is the
>> Sangean is probably not 50 ohms.
>
> Ah, but in reverse? :) I don't know if this is good thinking, but if the
> coax
> IS 50 ohms, could I not put the 50 ohm connection onto the coax and tweak
> the
> other end (on the input instead of the coax) impedance by watching the
> signal
> strength meter on the receiver?
>
Ideally you would adjust the impedance of the antenna to match 50 ohms
then attach your 50 ohm coax, then connect to a 50 ohm receiver. (you don't
have)
But trying to adjust an antenna that is way out there (say 4000 ohms with
200 Reactance)
from the shack is not an easy task.
> (Might be undeed according to posts people made earlier that suggest that
> losses here might matter less than what happens on the longwire end of the
> coax).
I'm in agreement with those that say just put up a wire and listen.
Then pick your favorite band and put up a resonant antenna and compare the
two.
Then your learning something.
Mike
Lostgallifreyan
news:9da56$4b2e9198$18ec6dd7$79...@KNOLOGY.NET:
>> (Might be undeed according to posts people made earlier that suggest
>> that losses here might matter less than what happens on the longwire
>> end of the coax).
>
> I'm in agreement with those that say just put up a wire and listen.
> Then pick your favorite band and put up a resonant antenna and compare
> the two.
> Then your learning something.
> Mike
>
Right now I have no idea what my favourite band might be. :) I'll try the
basic wire, I used to try that many years ago as a kid, in places where it
was easy, on private land with space for it. But that was the seventies, in
the country. Now I'm in an inner city full of mobile phones and computers,
things have changed so much that I know it won't be the same. I like that 18'
whip scheme you linked to though, I really like that one and want to try it.
amdx
Yes, I was a little diappointent, I remembered seeing a lot of other
antennas
from Dallas, but they seem to have been removed them from the site. I guess
once
he finds something that works better and is not terribly difficult to make,
he
drops previous setups.
Mike
Fred McKenzie
Lostgallifreyan <no-...@nowhere.net> wrote:
> Right now I have no idea what my favourite band might be. :) I'll try the
> basic wire, I used to try that many years ago as a kid, in places where it
> was easy, on private land with space for it. But that was the seventies, in
> the country. Now I'm in an inner city full of mobile phones and computers,
> things have changed so much that I know it won't be the same. I like that 18'
> whip scheme you linked to though, I really like that one and want to try it.
Lost-
I agree that the "basic wire" antenna approach will almost certainly
work. At least you will get your feet wet. That is the kind of
external antenna most often used with that type of radio.
If you want to continue the search for input impedance, consider trying
something like an MFJ Antenna Analyzer (MFJ-259 or 269?), which uses a
sufficiently low signal level that it shouldn't hurt the radio. Instead
of analyzing the antenna, use it to analyze the input of the radio. You
can use the information to design a matching circuit, but you may find
that the improvement is disappointing for reasons already discussed.
Fred
K4DII
Lostgallifreyan
news:g4isi5ds5lkfl5q21...@4ax.com:
> You might shoot an email to tech at C.Crane Co. -- a lot of their
> branded radios are actually customized Sangeans...they might be able
> to tell you the most effective antenna and/or the impedance of the
> thing.
>
> bob
> k5qwg
>
I got a reply, but Sangean didn't tell them that either. :) But he says what
many here do, that it doesn't matter that much, and that 50 ohm line should
be ok.
One thing that keeps coming up is the need to make my own transformer for the
far end, whatever scheme I use, and in that context I often see mention of a
ferrite core: Amidon FT-114-75 (AL about 3000, permeability u=5000, about
1.14 inch outside diameter as described on one page). Cheap but apparently
not easy to find in Britain. Does anyone know a current source of something
equivalent to it? It's beginning to look like I should get a small handful of
them. Another thing that might be better fetched locally is something like
the broadband preamp for LW to >30 MHz sold by Kiwa Electronics. If anyone
knows of one, please point me to it.. It's a Norton balanced input amp with
gain of around 10 dB. Even if I don't need it I'd like to know where to find
such things locally. I can likely build something based on the Dallas design
in a PDF I found but a good picture of the construction would help, as I
can't easily visualise the coil and former arrangements from the schematic.
Lostgallifreyan
news:fmmck-03732B....@nntp.aioe.org:
I'll pass. :) I think the reason no-one knows is that as you (and others)
say, it's not important enough. What does seem important is to try to reduce
localised noise, and to break the current link to protect the radio input
from static discharges. Whether I use coax or a balanced loop made from
speaker wire, it loooks like my next step is to get Amidon FT-114-75 ferrite
cores to play with, and in Britain I can't easily do that, but if anyone
knows a local direct equivalent to them I can try that. I'll Google for
things that fit the description (AL about 3000, permeability u=5000, about
1.14 inch outside diameter) but I think it's wise to ask here to try to save
time.
Dave Platt
Lostgallifreyan <no-...@nowhere.net> wrote:
>I'll pass. :) I think the reason no-one knows is that as you (and others)
>say, it's not important enough. What does seem important is to try to reduce
>localised noise, and to break the current link to protect the radio input
>from static discharges. Whether I use coax or a balanced loop made from
>speaker wire, it loooks like my next step is to get Amidon FT-114-75 ferrite
>cores to play with, and in Britain I can't easily do that, but if anyone
>knows a local direct equivalent to them I can try that. I'll Google for
>things that fit the description (AL about 3000, permeability u=5000, about
>1.14 inch outside diameter) but I think it's wise to ask here to try to save
>time.
You can probably at least start your experimentation using the common
sort of interference-suppression ferrites that are found in many
computer accessories - e.g. molded onto DC cords, VGA cables, USB
cables, and so forth. Here in the U.S. these are easily available at
electronics surplus stores, ham-fest flea markets, and other such
sources.
In my experience, these tend to be a ferrite mix such as type 43,
which is optimized for use at somewhat higher frequencies than
HF/SWL... so they will probably not be optimal for your purposes.
However, they can be made to work.
A few years ago I constructed a common-mode feedline choke for our
local ARES/RACES ham station, to try to keep 40- and 80-meter signals
from being carried back down the outside of the coax and into the
building (our signal was audible on phones in the city's "911"
emergency dispatch center... *not* good). I took several tubular
computer-interference-suppression ferrite cores (large inner
diameter), glued them end-to-end with cyanoacrylate, let them dry, and
then ran some RG-8X coax through the center and back around the
outside and through the center again. The coax looped through the
tube of ferrites three times.
This resulted in an extremely effective common-mode choke. According
to my MFJ antenna analyzer, the impedance looking up through the coax
in the usual way (standard hookup, into a 50-ohm dummy load) was 50
ohms... the ferrites had no effect at all on the differential-mode
signal in the coax.
But, when I measured the impedance along the braid (i.e. from the
ground shell at one end of the coax, to the ground shell at the other...
a DC short circuit), I couldn't get a reading at any frequency... the
meter just said "> 1500 ohms". Even at the lowest frequency of
interest, these non-optimal ferrites added so much inductance to the
common-mode signal path that they were blocking the feedline current
flow very effectively.
[Unfortunately, we determined that the phone interference was caused by
direct RF pickup by the phone wiring, which was in the "near field" of
the antenna above the roof. It occurred even if we completely
disconnected the building feedline, and fed the antenna directly from
a radio located up on the roof. The feedline choke couldn't help us.]
In your situation, I'd guess that you could probably make an efficient
feedline choke by using almost any surplus ferrite toroid which is
sufficiently large to wind your feedline (coax or speaker wire)
through it a few times. Or, use several surplus ferrite cores,
end-to-end, and if they're large enough in diameter, loop the feedline
down through the center more than once.
It won't be perfect (nor as good as if you used a ferrite optimized
for use at lower frequencies) but it will probably help matters, and
will give you some sense as to whether it makes sense to go to the
trouble and expense of buying ferrites that are better for your purpose.
Lostgallifreyan
> In article <Xns9CEB6866757...@216.196.109.145>,
> Lostgallifreyan <no-...@nowhere.net> wrote:
>
>>I'll pass. :) I think the reason no-one knows is that as you (and
>>others) say, it's not important enough. What does seem important is to
>>try to reduce localised noise, and to break the current link to protect
>>the radio input from static discharges. Whether I use coax or a balanced
>>loop made from speaker wire, it loooks like my next step is to get
>>Amidon FT-114-75 ferrite cores to play with, and in Britain I can't
>>easily do that, but if anyone knows a local direct equivalent to them I
>>can try that. I'll Google for things that fit the description (AL about
>>3000, permeability u=5000, about 1.14 inch outside diameter) but I think
>>it's wise to ask here to try to save time.
>
> You can probably at least start your experimentation using the common
> sort of interference-suppression ferrites that are found in many
> computer accessories - e.g. molded onto DC cords, VGA cables, USB
> cables, and so forth. Here in the U.S. these are easily available at
> electronics surplus stores, ham-fest flea markets, and other such
> sources.
>
> In my experience, these tend to be a ferrite mix such as type 43,
> which is optimized for use at somewhat higher frequencies than
> HF/SWL... so they will probably not be optimal for your purposes.
> However, they can be made to work.
>
A complete ring is better, air gaps might make it harder to assess how good
it is unless you know enough (or have equipment) to make comparisons. I
don't. :) But I did find an appropriately sized type 43 ferrite ring on eBay
and put it on my watch list a few hours ago, so I guess this is what I'll buy
if I don't find better quickly. The seller has a few, I think.
I hadn't thought of this for common mode noise suppression but I will try it,
sounds like a good idea. The rings I'm after are for the coupling at each end
of the line though, 9:1 or 10:1 at far end, 1:1 at receiver end. But I guess
that the clamp-on ferrite slug could be useful on the balanced line loop
that runs between the rings. I've also wondered if that balanced line might
better be a twisted pair with each twist perhaps 10 cm or so long to be sure
that common mode really is common, but I have no idea if that's wise or
required. Haven't seen anything to suggest I need to do it.
> It won't be perfect (nor as good as if you used a ferrite optimized
> for use at lower frequencies) but it will probably help matters, and
> will give you some sense as to whether it makes sense to go to the
> trouble and expense of buying ferrites that are better for your purpose.
>
80 turns.. plus another 8 for the secondary.. I read they should be close
turns, and the ring size was probably specified mainly to accomodate them
all. I will try other ferrites and carbonyl iron power type cores and
whatever else comes my way perhaps, I found four small toroids in a broken
computer SMPU that might be fun to try. Ultimately though, I'm aiming for
best shots because it's like plotting an unknown graph curve with only a few
samples, so the better the accuracy of each move, the better I can understand
any discrepancy in any one of those moves.
I have a basic philosophy that is similar to Jeff Liebermann's 'Learn By
Destroying' thing, as I also used to take stuff apart as a kid, and destroyed
plenty, but actually apart from seeing what sort of build quality was
acceptable and how discrete components were built, I didn't learn much
beyond tool handling, the thing that taught me most was when I took apart
something I had to put together again for fear of punishment if I failed and
got found out. So the closer I get to starting with something like an ideal
working part or whole, the faster I can figure out the meaning of significant
excursions from that ideal. It's kind of like the argument of whether a kid
should get his first bike new and working, or self-built from bits. I think
the first way is right because it's the fastest way to know what working
(and safety) really is, then start changing things, knowing what path was
taken and how to get back without help. Works great with computers too...
JIMMIE
> Does anyone know what the Sangean ATS-909's external antenna input impedance
> is?
>
> schematics, service manuals, reviews, but no straight word on the impedance
> of that input! (Not even in the service manual specs). The only reference I
> found was a from a guy on a 7-page set of ham reviews, and all he said was
> that it was a mystery!
>
> Maybe the only way to know is to start from the schematic but I don't know
> how, but here's the best schematic I could find:http://eric.horsemensociety.info/TECH/images/ATS909_Schematic_A.gif
> (Antenna input is near top right).
> (Link appears to be dead, 403, forbidden. I'm sure it worked last week..)
>
> What I really want to know is whether the ATS-909 will work ok with a
> long(ish) wire outside feeding a 50 ohm coax via a 9:1 transformer, or if
> that would cause more bother than connecting a wire directly to it and
> putting up with local noise picked up from nearby buildings.
Ive measured the input impedance of a few SW receivers and found them
to be in the 1Kohm ballpark for the most part. I did this by applying
a voltage through a series resistor to the frontend of the radio and
adjusting the value of the resistor until the voltage dropped by 50%.
If you have a schematic an analysis of the front end circuit might
give you and idea.
Jimmie
Lostgallifreyan
62b2e0...@s31g2000yqs.googlegroups.com:
> Ive measured the input impedance of a few SW receivers and found them
> to be in the 1Kohm ballpark for the most part. I did this by applying
> a voltage through a series resistor to the frontend of the radio and
> adjusting the value of the resistor until the voltage dropped by 50%.
> If you have a schematic an analysis of the front end circuit might
> give you and idea.
>
Ok. That fits with the 1K pot for RF attenuation in that radio, someone
mentioned this and I wasn't sure if other parts might alter the picture, but
I guess not by anything that matters. I'll be using a ferrite at the radio
end of a balanced line so I guess I can experiment with turns count and watch
the signal strength meter. Might not even need a preamp if that works.
If I'm thinking wrong, please stop me before I crash into something. :)
Dave
>
> What I really want to know is whether the ATS-909 will work ok with a
> long(ish) wire outside feeding a 50 ohm coax via a 9:1 transformer, or if
> that would cause more bother than connecting a wire directly to it and
> putting up with local noise picked up from nearby buildings.
lets go back to the beginning... this is what i would do.
1. hook up whatever coax you have to the radio and run it as far
outside away from the house as it will go.
2. hook up a wire directly to it as long as you can go in whatever
random direction you may be able to go
3. enjoy.
if in the future there are signals that just aren't strong enough, but
still above the local noise, then start playing around with either a
matching network or a preamp. but until you know how well the
receiver by itself works with the plain wire/coax you are wasting time
over designing something you probably won't need.
JIMMIE
You may find that a good RF ground more benificial than any particular
antenna. I discovered this while in the military and had a chance to
hook my little cheap portable Setico rx to an antenna made of 20ft of
emt conduit and the ground system on an abandoned comm unit. Lots of
good info arounf on RF grounds on the web and this group.
Jimmie
Jimmie
Richard Clark
<no-...@nowhere.net> wrote:
>What I really want to know is whether the ATS-909 will work ok with a
>long(ish) wire outside feeding a 50 ohm coax via a 9:1 transformer, or if
>that would cause more bother than connecting a wire directly to it and
>putting up with local noise picked up from nearby buildings.
Hello Dr,
Well, I've been on the East Coast for several weeks and am just
catching up with your particular problem (which is not too uncommon
for SWL'ers who post here).
Many suggestions have been useful, but some contra-indicate others,
while some merely rely on lore and superstition.
One of the last suggestions, from JIMMIE, is probably the single
greatest boon for signal strength: Ground. Ground is always the least
appreciated component, and is always the single most important one.
Ground for RF is not always the same as the ground for safety. Worse
yet is that mixing them can sometimes introduce grief (AKA ground
loops). ALL grounds should eventually find their way to the service
ground. This advice serves both safety and engineering. More can be
said - but we move on.
One antenna does not always work for all bands (not without a lot of
work and the ability to change its polarization). As such, two or
more antennas are necessary for SWL'ing. They don't need to be
isolated to one band, but if any antenna is resonant for one, it will
probably be difficult on another band that is twice or half that
frequency. Thus you add another antenna that is half or twice the
first's dimension. The benefit here is that they can be wired to the
same feed point with little interaction between them. More can be
said here too.
Matching with a one-size-fits-all doohickey is pabulum for the masses.
When it is tossed into the mix, it usually forces the user to add the
components already described above that are responsible for most of
the benefit attributed to the doohickey. Hosanna's are misplaced.
More can be said here, to not good outcome.
Matching with an antenna tuner (yes, I am aware of the irony in its
name) satisfies all issues (except for the transmission line loss - if
it matters) of matching. The tuner's responsibility is to see to it
that an unknown source is matched to an unknown load (that is why it
has so many adjustments). You can use any Ham grade tuner, get one
without a meter to save the big bucks. Whatever product that is
designed for the ham bands is satisfactory for the SWL bands. Of
course, you could build your own (what a concept!).
Matching with a preselector takes the antenna tuner one step further,
and protects your receiver from the scourge of these "modern" designs:
intermod. The SWL-monkeys who demand the ability to "quickly" tune up
different bands/frequencies usually whine and squeel about the
difficulty of tuners and preselectors (and in the same breath praise
the doohickey's font of blessings). I let them indulge in their
illusions and say no more.
INTERMOD is the silent killer (as they used to say about high blood
pressure). A strong station (a nearby AM transmitter in town) can
easily close down your 31M listening experience by simply driving the
AGC into overload without you being aware of it. Preselectors and
Tuners will drive down that off-band signal, peak the selected
frequency, and give you what you tuned for in that band. Beware of
imitations that suggest they do the same without tuning (what a
crock).
As for that antenna impedance. Others have suggested a myriad of
possibilities. The first active component's shunt reactance (often
the base-emitter capacitance) is the limiting factor even when
humongous resistance bridges those same points. Resistance is for
bias folks. More can be said, but enough has been said here.
Feel free to ask for more to be said.
73's
Richard Clark, KB7QHC
Lostgallifreyan
news:t33vj597ol4oc0kpl...@4ax.com:
Thanks. :) Well, my plan is to use a ground at the antenna end, right
underneath it. My neighbourhood problems recently were solved when a guy on
the first floor pissed off someone enough that said someone blew their flat
door in with a shotgun! So the whole problem ended with a neat flameout a
few days ago. I couldn't go out there rigging antennae while paranoid
criminals were still active, it's seriously asking for BAD trouble. Right now
I have the lesser problems of dental and other bills imminent, but I'll get a
good 4' ground rod and rig up an 18' vertical whip as I learned of in details
I posted about earlier. I understand that good reception depends on a good
compromise between selectivity and sensitivity, and no doubt the antenna
'tuner' helps with that, though I'll mainly be concerned with good ground and
local common mode noise rejection. My first attempt at the line between
antenna and receiver will be a balanced line with a toroid at each end for
current isolation and possibly the suggested Norton preamp on the receiver
input, but I'll try without it first as I suspect I'll get enough signal
strength to satisfy me for a while. If I have to use coax I will but I'll try
the easier options first. This basic plan does involve a 10:1 ratio in
windings on the far end toroid which should help smooth out peaks of
resonance as described by John Doty and others as mentioned before, and if
nothing else, drives a stronger current in the balanced line part of the
system. I'm no longer much concerned about matching impedances, but I will be
watching for results of changing antenna length if resonance seems to be an
issue. My interest in the 'doohickey' or any other widget was mainly in what
appeared to be a means of reducing the difference in signal strength extremes
due to resonance. I understand that if I subsequently have to select the
weaker of two close stations I'll either have to add some 'trap' for a
specific offender, such as a trimmed lengh of unterminated coax (though as
far as I know, that trick is usually reserved for much higher frequencies),
or use a manually tuned system which I'll explore if it becomes a dominant
concern.
Richard Clark
<no-...@nowhere.net> wrote:
>Well, my plan is to use a ground at the antenna end, right
>underneath it.
This bodes ill if you do not tie that ground directly to the service
ground. Further, a "ground" as you describe it (incompletely) sounds
suspiciously like a ground rod. This is NOT the same thing as RF
ground - not even close unless you live within several meters of low
tide along a major ocean shore.
>I'll get a
>good 4' ground rod and rig up an 18' vertical whip as I learned of in details
>I posted about earlier.
Suspicions confirmed....
> I understand that good reception depends on a good
>compromise between selectivity and sensitivity, and no doubt the antenna
>'tuner' helps with that, though I'll mainly be concerned with good ground and
>local common mode noise rejection.
This does not acknowledge the significance of INTERMOD problems.
Experience may have to teach that (when you make all these
improvements and have poor results for your effort).
>My first attempt at the line between
>antenna and receiver will be a balanced line with a toroid at each end for
>current isolation
This is a very, very curious novelty. You do not describe a
"balanced" system with a ground rod and vertical, so any effort at
"balanced" lines is window dressing only. The reason for placing
"balanced" within quotes is due to the inordinate care and skill
required in obtaining a balanced design. It is more often achieved
with coax. Too often, "balanced line" is approached with the
mysticism of universal relief for whatever ails a listener.
>and possibly the suggested Norton preamp on the receiver
>input,
I must have missed that posting. Sounds like another elaboration.
>but I'll try without it first as I suspect I'll get enough signal
>strength to satisfy me for a while. If I have to use coax I will but I'll try
>the easier options first. This basic plan does involve a 10:1 ratio in
>windings on the far end toroid which should help smooth out peaks of
>resonance as described by John Doty and others as mentioned before, and if
>nothing else, drives a stronger current in the balanced line part of the
>system.
This is the doohickey I spoke of. It is basically the refuge
accessory of the lowfers where the span of frequencies is, maybe,
three to one and not like the ten to one of HF SWLing.
>I'm no longer much concerned about matching impedances, but I will be
>watching for results of changing antenna length if resonance seems to be an
>issue.
This is at cross purposes. You don't have many realistic options of
changing antenna length (height) as you do with a simple tuner when it
comes to matching.
>My interest in the 'doohickey' or any other widget was mainly in what
>appeared to be a means of reducing the difference in signal strength extremes
>due to resonance. I understand that if I subsequently have to select the
>weaker of two close stations I'll either have to add some 'trap' for a
>specific offender, such as a trimmed lengh of unterminated coax (though as
>far as I know, that trick is usually reserved for much higher frequencies),
>or use a manually tuned system which I'll explore if it becomes a dominant
>concern.
Traps don't work very well for adjacent AM/SSB stations, you need
cascade XTAL ladders to do that. Tuners, also, can only operate
within the combination of number of reactive elements and Q.
Please respond to your perception of the problem of INTERMOD as it is,
as I said, the silent killer of reception.
Lostgallifreyan
I haven't a clue about intermod, yet. One thing at a time. Right now I see at
least three contradictions (re ground rods, transformers, and feedlines) with
advice from several people, one of which (the guy who wrote the description
of the antenna and balanced line I mentioned) is part of a group of hams who
is turned to for advice by the others. No guarantee of correctness, perhaps,
but if I keep on being told I'm wrong when my stuff is coming as directly as
I can get it from others with experience, then as far as I'm concerned I'll
do what I think best and get out of the crossfire. Specifically, many times
I've seen advice that service grounds are not adequate because of common mode
noise and local currents, hence the ground rod you vehemently negate. I can
ground to service ground at near end but if the receiver is on batteries, not
connected to anything except a transformer coupling RF from the antenna, then
the ground only needs to be at the antenna end, according to advice I've seen
in several places. Even if I do ground to a water pipe or other local ground,
all advice I see until now insists on having a ground rod as close to the
antenna as possible, no matter what else I do, yet now you urge against this.
I will stop asking for advice if all I see is vigorous contradiction between
people who claim knowledge I do not have. Diverting that disagreement to one
with me doesn't alter this, I did not originate the info behind the choices I
am considering. Even if all the various contributors come here and duke it
out between them it appears I'll be none the wiser.
Lostgallifreyan
news:Xns9CF4ED6B8F0...@216.196.109.145:
> ...several people, one of which (the guy who wrote the description
> of the antenna and balanced line I mentioned) is part of a group of hams
> who is turned to for advice by the others.
To save time:
"http://www.kongsfjord.no/dl/Antennas/The%20Best%20Small%20Antennas%20For%20M
W,%20LW,%20And%20SW%20rev%202.pdf
The start page for that link is here;
http://www.kongsfjord.no/dl/dl.htm"
(Copied from a post by 'amdx' earlier in this thread). The line IS balanced,
as it carries only its own internal current, driven by an isolated coupling
with the antenna circuit. Anyway, if he's wrong, there's not much point in
taking it up with me, for obvious reasons. He wrote that. I didn't.
Lostgallifreyan
news:Xns9CF4EF8F07F...@216.196.109.145:
> He wrote that. I didn't.
Sorry amdx, potential for confusion there... I mean the guy who wrote what
you linked to..
Richard Clark
<no-...@nowhere.net> wrote:
>I haven't a clue about intermod, yet. One thing at a time.
The term Intermod is probably mis-direction if you research it.
Basically, if an nearby AM/FM/TV transmitter (and nearby can be on the
scale of several miles) happens to excite your antenna; then its
developed voltage will overload the frontend (Intermod follows, but
the products are not what I am emphasizing here). This overload can
be many, many kHz, or MHz from the intended and tuned signal; and yet
this frequency remote signal will develop an AGC that drives down gain
on your intended signal.
This characteristic is VERY common for untuned frontends in modern
receivers. It is not often noted for poor antennas (those whips, when
they are used for SW), but when a real antenna is attached *BINGO*
sensitivity goes down the toilet. By providing a tuned input, the
side-signal that would otherwise silently drive AGC is attenuated, and
AGC is developed only by the in-band signals.
>Right now I see at
>least three contradictions (re ground rods, transformers, and feedlines) with
>advice from several people, one of which (the guy who wrote the description
>of the antenna and balanced line I mentioned) is part of a group of hams who
>is turned to for advice by the others. No guarantee of correctness, perhaps,
>but if I keep on being told I'm wrong when my stuff is coming as directly as
>I can get it from others with experience, then as far as I'm concerned I'll
>do what I think best and get out of the crossfire.
A reasonable posture.
>Specifically, many times
>I've seen advice that service grounds are not adequate because of common mode
>noise and local currents, hence the ground rod you vehemently negate.
I don't negate its use, I say that it is NOT RF ground. If you tie
this ground rod to the service ground, then that wire will probably
act more in your behalf than either "ground." There is a world of
difference between safety grounds (what those rod-thingies are) and RF
grounds (which often don't go into ground at all).
Ground is a long and rich story that has been celebrated in this group
for years. It deserves respect and attention well beyond these few
words.
>I can
>ground to service ground at near end but if the receiver is on batteries, not
>connected to anything except a transformer coupling RF from the antenna, then
>the ground only needs to be at the antenna end, according to advice I've seen
>in several places.
To your specific arrangement - quite true. However, many who have
claimed to have made every precaution then connect their receiver to
an amplifier, computer, what-you-might-call-it and a new path to
ground winds its way through interesting environments that are RF
rich.
>Even if I do ground to a water pipe or other local ground,
>all advice I see until now insists on having a ground rod as close to the
>antenna as possible, no matter what else I do, yet now you urge against this.
I urge against mixing grounds. Such things arrive by the most benign
and seemingly inconsequential actions.
>I will stop asking for advice if all I see is vigorous contradiction between
>people who claim knowledge I do not have. Diverting that disagreement to one
>with me doesn't alter this, I did not originate the info behind the choices I
>am considering. Even if all the various contributors come here and duke it
>out between them it appears I'll be none the wiser.
Attention to one detail at a time helps, but a lot of this arrived
through responding to the query for antenna port Z. Those adjuncts
that massage input/output Z also fold in the discussion of ground.
Convention has it that you start a new thread for each side-topic that
drives you into conniptions. Asking about the facts and foibles of
ground would be a good start on a new thread - especially when Art's
wet-dreams descend into discussion of particle duality self
annihilation driving all participation away from antenna design. For
instance "Why are ground rods considered insufficient for RF
application?"
I am content to respond to either discussion.
Richard Clark
<no-...@nowhere.net> wrote:
>To save time:
>"http://www.kongsfjord.no/dl/Antennas/The%20Best%20Small%20Antennas%20For%20M
>W,%20LW,%20And%20SW%20rev%202.pdf
An example of invention driving the discussion rather than the need
being satisfied.
Simply put, there is absolutely no reason to use a "balanced" line. It
is window dressing for the circuit which IS balanced (and balanced for
no apparent reason for this unbalanced source). Metaphorically, it is
like adding a clutch to an automatic shift. Yes, you can do it. It
might appear to be elegant. It will certainly work. But why?
Try asking why the trappings of this novel design don't bring some
solution in a new thread. You might stumble at offering the problem
it pretends to solve. (I will anticipate it has something to do with
noise, THIS will certainly raise a lot of catcalls.)
Mike Kaliski
The Sangean ATS-909 along with similar radios are designed to resolve
signals from the whip antenna or in built ferrite antenna. Attaching 8 to 10
feet of wire to the whip will bring in more stations but depending on
location may well pick up so much extra signal as to cause intermodulation
and AGC limiting preventing reception of the weak signals you want to
receive.
As stated earlier, the front end of these receivers is wide open and the
front end is exposed to the complete spectrum of transmissions received by
the antenna.
There is nothing inherently wrong with the receiving system you have decided
upon but it will undoubtably overload your receiver with signals and you
will be puzzled as to why the reception seems poorer with more noise pickup
rather than less.
As Richard has stated you need some form of preselection to filter out the
unwanted signals before they get into your radio. Basically this is a
tuneable filter which only allows through a single band of frequencies at a
time. The following site explains the essentials.
http://www.dxing.com/tnotes/tnote07.pdf
You can buy commercial preselectors but they will probably cost as much as
your radio. As they are generally passive devices built from a set of
switched coils and a variable capacitor they last forever and old ones do
come up from time to time at junk sales and the like. It is possible to make
a simple filter to cover just one or two bands that interest you.
By all means, try the external antenna system but be prepared to buy a
'better' receiver with front end band pass filters or a preselector.
You can have too much of a good thing when it comes to receiving antennas. A
bigger receiving antenna won't bring in signals from further away. If they
are there, the receiver is probably sufficiently sensitive to pick them up
already. What the bigger antenna will do is raise the level of all the
signals it is picking up and feeding into the receiver and that includes
noise, and other unwanted stations. That is why you need additional
filtering to cut down the unwanted signals and allow your receiver a fair
chance of demodulating what you actually want to hear.
Regards
Mike G0ULI
Lostgallifreyan
> On Sat, 02 Jan 2010 17:20:24 -0600, Lostgallifreyan
> <no-...@nowhere.net> wrote:
>
>>I haven't a clue about intermod, yet. One thing at a time.
>
> The term Intermod is probably mis-direction if you research it.
> Basically, if an nearby AM/FM/TV transmitter (and nearby can be on the
> scale of several miles) happens to excite your antenna; then its
> developed voltage will overload the frontend (Intermod follows, but
> the products are not what I am emphasizing here). This overload can
> be many, many kHz, or MHz from the intended and tuned signal; and yet
> this frequency remote signal will develop an AGC that drives down gain
> on your intended signal.
>
> This characteristic is VERY common for untuned frontends in modern
> receivers. It is not often noted for poor antennas (those whips, when
> they are used for SW), but when a real antenna is attached *BINGO*
> sensitivity goes down the toilet. By providing a tuned input, the
> side-signal that would otherwise silently drive AGC is attenuated, and
> AGC is developed only by the in-band signals.
>
Ok, this is cool, I understand that, and I also see that it doesn't really
concern intermodulation products as the initial problem is a bigger one if it
occurs. Can't help wondering why a receiver doesn't do some tuning before the
AGC for exactly this reason, but never mind...
>>Right now I see at
>>least three contradictions (re ground rods, transformers, and feedlines)
>>with advice from several people, one of which (the guy who wrote the
>>description of the antenna and balanced line I mentioned) is part of a
>>group of hams who is turned to for advice by the others. No guarantee of
>>correctness, perhaps, but if I keep on being told I'm wrong when my
>>stuff is coming as directly as I can get it from others with experience,
>>then as far as I'm concerned I'll do what I think best and get out of
>>the crossfire.
>
> A reasonable posture.
>
>>Specifically, many times
>>I've seen advice that service grounds are not adequate because of common
>>mode noise and local currents, hence the ground rod you vehemently
>>negate.
>
> I don't negate its use, I say that it is NOT RF ground. If you tie
> this ground rod to the service ground, then that wire will probably
> act more in your behalf than either "ground." There is a world of
> difference between safety grounds (what those rod-thingies are) and RF
> grounds (which often don't go into ground at all).
>
> Ground is a long and rich story that has been celebrated in this group
> for years. It deserves respect and attention well beyond these few
> words.
>
True, I don't doubt that for an instant, but it's also a question of what is
practical, and what is recomended by most people I've read words from at
times during the last 30 years or more. While I know that CB'ers would just
stick a magmount on their car's steel rooftop as often as not, and have read
of other schemes that place some small horizontal plate below the antenna,
there's a lot of scope between that and a rod driven into salty ocean
shoreline. Most people I ever came across asserted the importance of a ground
rod local to the antenna to couple with the local water table which is as
close as most ever get to the ocean unless they really like getting their
feet wet while they sit around at home. The proximity is as close to the
point where they want to pick up RF as they're going to get, and means less
noise from buildings full of electrical stuff picked up on metal between
antenna and whatever other ground might be provided elsewhere. This has been
the ONE common factor in pretty much everything I've seen on land-based AM
reception. Anything that directly appears to negate that advice makes it hard
to know what to trust, and certainly needs to be clearly explained.
>>I can
>>ground to service ground at near end but if the receiver is on
>>batteries, not connected to anything except a transformer coupling RF
>>from the antenna, then the ground only needs to be at the antenna end,
>>according to advice I've seen in several places.
>
> To your specific arrangement - quite true. However, many who have
> claimed to have made every precaution then connect their receiver to
> an amplifier, computer, what-you-might-call-it and a new path to
> ground winds its way through interesting environments that are RF
> rich.
>
I agree. The moment I try to connect to a system that includes a computer,
mixer, multiple supply grounds, as mine does, I'll be using a local
service ground and improving it the same as I would for audio, though it's
currently ok for that, at least. It already uses a star grounding system
where possible, as recommended by audio studio designers and others. There's
actually a supply ground rod outside the front door too, which presumably
helps more than the original wiring 15 years ago which didn't have that. (But
note below, where I mention isolation).
>>Even if I do ground to a water pipe or other local ground,
>>all advice I see until now insists on having a ground rod as close to
>>the antenna as possible, no matter what else I do, yet now you urge
>>against this.
>
> I urge against mixing grounds. Such things arrive by the most benign
> and seemingly inconsequential actions.
>
Hence the star network I mentioned, advised for audio setups.. It's kind of
why I wonder about what many suggest, grounding a coax at both ends, and even
in the middle if you want, and certainly to bury it. More importantly it's
why the Dallas Lankford design appeals to me. Isolation baluns that transfer
energy rather than use direct contact coupling look like a good way to avoid
the ground problems while also avoiding local noise pickup because the twin
cable will have good common mode rejection as it passes into the electrically
noisy bulding. (Though I can't help wondering if Dallas Lankford also tried
balanced microphone cable with a screen grounded at one end, just to see what
happened) Such methods have long been used in audio; is RF below 30 MHz
really so different in this case? So long as that line doesn't have dire
resonances of it's own, isn't attenuation the only big risk? Dallas Lankford
certainly thinks it works after working with it for at least 2 years. He says
that if you do it as described it will be low noise. (As opposed to
'reducing'). I don't think he's claiming any means of reduction, just saying
it's lower relative to inherently noisier systems, if wired as decribed.
Based on what I know, the claim seems good.
>>I will stop asking for advice if all I see is vigorous contradiction
>>between people who claim knowledge I do not have. Diverting that
>>disagreement to one with me doesn't alter this, I did not originate the
>>info behind the choices I am considering. Even if all the various
>>contributors come here and duke it out between them it appears I'll be
>>none the wiser.
>
> Attention to one detail at a time helps, but a lot of this arrived
> through responding to the query for antenna port Z. Those adjuncts
> that massage input/output Z also fold in the discussion of ground.
>
Agreed. But this is why instead of asking more questions whose answers I am
probably not prepared for, I described the simplest and apparently best
scheme I'd learned of so people see it whole and work from there...
> Convention has it that you start a new thread for each side-topic that
> drives you into conniptions.
Ah. :) Well, I thought that's exactly what would annoy people most. If
something directly arises from discussion in a thread, most people tend to
keep it there. I already do start a new one if I'm certain the issue is
different, and if I'm originating it.
> Asking about the facts and foibles of
> ground would be a good start on a new thread - especially when Art's
> wet-dreams descend into discussion of particle duality self
> annihilation driving all participation away from antenna design. For
> instance "Why are ground rods considered insufficient for RF
> application?"
>
> I am content to respond to either discussion.
>
> 73's
> Richard Clark, KB7QHC
>
Well, sure, if I am asking a direct technical or practical question. But
while I'm still slightly reeling from what appears to be a dissention with
what otherwise appears to be good advice, I like to keep the discussion in
one place, otherwise confusion reigns and spreads to many threads. Trust me,
that might annoy people. :) At least in this thread it might be useful to
anyone who has that radio.
Lostgallifreyan
news:NZCdnRc0Svn-c6LW...@bt.com:
> There is nothing inherently wrong with the receiving system you have
> decided upon but it will undoubtably overload your receiver with signals
> and you will be puzzled as to why the reception seems poorer with more
> noise pickup rather than less.
>
One reason I chose it is that it isn't trying that hard for extreme signal
capture. It appeared to be small, easy to use where I have limited space, and
include a transformer that I have read in numerous places partially solves
one of the main reasons for strongly differing signal strength with
frequency.
> As Richard has stated you need some form of preselection to filter out
> the unwanted signals before they get into your radio. Basically this is
> a tuneable filter which only allows through a single band of frequencies
> at a time. The following site explains the essentials.
>
> http://www.dxing.com/tnotes/tnote07.pdf
>
Looks good, I'm not keen on lots of widgets as it happens, fewer and better
widgets that co-operate well works better for me.
> You can buy commercial preselectors but they will probably cost as much
> as your radio. As they are generally passive devices built from a set of
> switched coils and a variable capacitor they last forever and old ones
> do come up from time to time at junk sales and the like. It is possible
> to make a simple filter to cover just one or two bands that interest
> you.
>
> By all means, try the external antenna system but be prepared to buy a
> 'better' receiver with front end band pass filters or a preselector.
>
The pre-selection thing isn't a problem, I can see why that helps, and did so
much earlier than now. The point that disconcerts me strongly is what appears
to be significant difference of opinion between experts, especially when it
applies to things as well established as ground rods. Again, this is why I
won;t just ask questions. Context is clearly everything, so instead I
describe the whole scheme I'm considering. Ultimately it's quicker that way.
Richard Clark
<no-...@nowhere.net> wrote:
>
>Most people I ever came across asserted the importance of a ground
>rod local to the antenna to couple with the local water table which is as
>close as most ever get to the ocean unless they really like getting their
>feet wet while they sit around at home.
In fact, this almost always NEVER happens. Skin effect defines the
layer depth of RF in ground. An 8 foot rod is like a splinter when
you are trying to harpoon a Blue Whale.
Ground rod engineering has been discussed in this forum to great depth
(pun intended, or not). The rods are as well understood as water
witching forks. In the HF region, single or several rods have no
practical RF use whatever. Above HF, absolutely no one gives them any
thought.
>The proximity is as close to the
>point where they want to pick up RF as they're going to get, and means less
>noise from buildings full of electrical stuff picked up on metal between
>antenna and whatever other ground might be provided elsewhere. This has been
>the ONE common factor in pretty much everything I've seen on land-based AM
>reception. Anything that directly appears to negate that advice makes it hard
>to know what to trust, and certainly needs to be clearly explained.
When you can't do anything else that is effective, a ground rod seems
like more than enough. It is certainly a need for safety's sake,
especially when your vertical could be a lightning magnet. Consider
that same antenna: is it directly GROUNDED? Or is it floating? If
ground is a panacea, I bet most of your advisors immediately isolate
their antenna from it. One has to wonder about faith....
Either design works with equal efficiency. You simply need a coupling
system to the grounded antenna design. One method is using a folded
monopole. Other methods abound (which are often confined to yagi
driven element discussion, but are eminently applicable here).
>The moment I try to connect to a system that includes a computer,
>mixer, multiple supply grounds, as mine does, I'll be using a local
>service ground and improving it the same as I would for audio, though it's
>currently ok for that, at least. It already uses a star grounding system
>where possible, as recommended by audio studio designers and others. There's
>actually a supply ground rod outside the front door too, which presumably
>helps more than the original wiring 15 years ago which didn't have that. (But
>note below, where I mention isolation).
The Star system is great for exactly as you understand and describe
it, but for antenna applications that remote ground could act as a
suicide adapter if it does not have its own path to the service
ground. Yes, this violates the star, but when path lengths include a
lot of resistance and leakage current, voltages can become
considerable when you supply a new avenue through your home. This is
the story of the classic ground loop.
>Hence the star network I mentioned, advised for audio setups.. It's kind of
>why I wonder about what many suggest, grounding a coax at both ends, and even
>in the middle if you want, and certainly to bury it. More importantly it's
>why the Dallas Lankford design appeals to me. Isolation baluns that transfer
>energy rather than use direct contact coupling look like a good way to avoid
>the ground problems while also avoiding local noise pickup because the twin
>cable will have good common mode rejection as it passes into the electrically
>noisy bulding. (Though I can't help wondering if Dallas Lankford also tried
>balanced microphone cable with a screen grounded at one end, just to see what
>happened) Such methods have long been used in audio; is RF below 30 MHz
>really so different in this case? So long as that line doesn't have dire
>resonances of it's own, isn't attenuation the only big risk? Dallas Lankford
>certainly thinks it works after working with it for at least 2 years. He says
>that if you do it as described it will be low noise. (As opposed to
>'reducing'). I don't think he's claiming any means of reduction, just saying
>it's lower relative to inherently noisier systems, if wired as decribed.
>Based on what I know, the claim seems good.
I'm not familiar with Dallas Lankford, but isolation and shielding
techniques are topics I have visited professionally throughout the
years and they are not simple. Without a concommitant discussion of
the noise source, one wrong ground selection can wipe out all pursued
benefits. Let's revisit one of your statements above:
>balanced microphone cable with a screen grounded at one end
Which end? Any choice stands an equal chance of being the wrong
choice.
Richard Clark
wrote:
>I'm not familiar with Dallas Lankford
I have since visited your suggested page to casually view his works.
Interesting set of circuits too (although, some of the phasing systems
have been superceded with shift registers - I used to use
bucket-brigade chips).
I was especially touched to see wide coverage of the R390A. It was
the subject of my first class that I taught in the Navy (along with
the Collins URC-32). Cadillac equipment. I note in his discussion of
stabilizing the BFO, he uses a Rubidium standard for comparison. I
calibrated quite a few of those Rubidium standards too with my Cesium
Beam whenever a Boomer came along side. An URQ-12 would have worked
as easily, but this discussion no doubt exceeds the capacity of your
wallet (the Navy provided such a candy store for my Metrology Lab).
Lostgallifreyan
> On Sun, 03 Jan 2010 05:26:32 -0600, Lostgallifreyan
> <no-...@nowhere.net> wrote:
>
>
>>
>>Most people I ever came across asserted the importance of a ground
>>rod local to the antenna to couple with the local water table which is
>>as close as most ever get to the ocean unless they really like getting
>>their feet wet while they sit around at home.
>
> In fact, this almost always NEVER happens. Skin effect defines the
> layer depth of RF in ground. An 8 foot rod is like a splinter when
> you are trying to harpoon a Blue Whale.
>
> Ground rod engineering has been discussed in this forum to great depth
> (pun intended, or not). The rods are as well understood as water
> witching forks. In the HF region, single or several rods have no
> practical RF use whatever. Above HF, absolutely no one gives them any
> thought.
>
True. I'm interested in using a single antenna for all of LW up to around 30
MHz as a simple starting point though, so Dallas Lankford's scheme seems to
fit the bill.
>>The proximity is as close to the
>>point where they want to pick up RF as they're going to get, and means
>>less noise from buildings full of electrical stuff picked up on metal
>>between antenna and whatever other ground might be provided elsewhere.
>>This has been the ONE common factor in pretty much everything I've seen
>>on land-based AM reception. Anything that directly appears to negate
>>that advice makes it hard to know what to trust, and certainly needs to
>>be clearly explained.
>
> When you can't do anything else that is effective, a ground rod seems
> like more than enough. It is certainly a need for safety's sake,
> especially when your vertical could be a lightning magnet. Consider
> that same antenna: is it directly GROUNDED? Or is it floating? If
> ground is a panacea, I bet most of your advisors immediately isolate
> their antenna from it. One has to wonder about faith....
>
Safety is important, even though lightning strike isn't that big a risk here.
Actually it's risen because nearly all large trees have been removed in the
last two years, and I'd be held reponsible for any damage caused that way.
If you look at that PDF you'll see the 15' whip antenna is directly connected
to ground through 80 turns of wire on a ferrite toroid. I might add a spark
gap in parallel as that wire is not a high current path. So long as it is
much more likely to go to ground rather than along the line in to the house,
I'll have done what I'm supposed to do. The trouble would only exist (other
than unpreventable natural excesses) if it were evident that I had not done
this.
> Either design works with equal efficiency. You simply need a coupling
> system to the grounded antenna design. One method is using a folded
> monopole. Other methods abound (which are often confined to yagi
> driven element discussion, but are eminently applicable here).
>
That PDF shows the coupling in this case. It's similar to other ideas
recommended for similar small SW listening setups. Once I have all I need to
try it I'm just as happy to try experimenting to see what happens as to try
any plan. There are some limits though, the location is too built up to
expect much from anything intended to be directional. I'm just intending to
look around, not looking out there for something specific.
>>The moment I try to connect to a system that includes a computer,
>>mixer, multiple supply grounds, as mine does, I'll be using a local
>>service ground and improving it the same as I would for audio, though
>>it's currently ok for that, at least. It already uses a star grounding
>>system where possible, as recommended by audio studio designers and
>>others. There's actually a supply ground rod outside the front door too,
>>which presumably helps more than the original wiring 15 years ago which
>>didn't have that. (But note below, where I mention isolation).
>
> The Star system is great for exactly as you understand and describe
> it, but for antenna applications that remote ground could act as a
> suicide adapter if it does not have its own path to the service
> ground. Yes, this violates the star, but when path lengths include a
> lot of resistance and leakage current, voltages can become
> considerable when you supply a new avenue through your home. This is
> the story of the classic ground loop.
>
Well, a ground rod isn't going to cost much, and making and breaking
connections to it is one of the easiest and cheapest things I'll be able to
do, so I'll test that empirically when I'm ready. I won't try to predict it
now. Whenever I find some new ground noise problem in anything I do here, I
usually manage to isolate it and solve it acceptably within an hour or less,
so I'll trust my chances. Usually the purpose hasn't been for RF, but quite
often the sources did involve RF too so my instincts might help me more than
my knowledge.
Well, I did think of that. :) And I didn't state it because I didn't know for
sure. As I imagine that local RF couplings from various digital devices might
place small currents on the local ground, I imagine that grounding a shield
at the remote ground makes sense. Doesn't matter to me though. It's far
easier and faster to experiment than to try to predict because there are only
two ways to try. Dallas Lankford directly states that no shield is even
required, and I doubt he'd have said that if he couldn't demonstrate it, and
as that line is a two-wire loop that has no direct contact with anything, it
should reject any common mode noise that hits it. Even in audio this matters
because the same method is used to reject RF pickup on audio lines. I think
some people persist in baluns instead of op-amp common mode rejection specs
for this reason, despite the chances of modest distortion in audio bands from
the transformers used. Not entirely relevant but it illustrates how people
can find themselves choosing between two less-than-ideal circumstances for
best effect.
I understand that noise context matters for a real attempt to plan for it,
but that's far more difficult that presenting the basic antenna scheme.
Lostgallifreyan
Not just my wallet. :) This is cool though, I have encountered both bucket
brigade IC's and shift registers. Offtopic question: Did the bucket brigade
lead directly to the switched capacitor filter? I ask because they seem
related, and the BB seems to have become obsolete, but the SCF, anything but.
Richard Clark
<no-...@nowhere.net> wrote:
>Did the bucket brigade
>lead directly to the switched capacitor filter?
Same thing if I read you correctly.
Lostgallifreyan
news:Xns9CF5C304F98...@216.196.109.145:
> It was
>> the subject of my first class that I taught in the Navy
Curious... You might have experiences that give useful insight into something
I'm discussing in another group, some off-the-wall topic I entered into
during a quiet new-year's moment in alt.lasers... I can accept that you might
not want to get into that at all once you see it but if you do I welcome the
input because as I state there, one issue is to find helpful signals rather
than the noise such discussions usually provoke. But it might be a lengthy
misdirection if you're busy so I won't push the point. But I will say now
that my dad was a naval officer when he was younger and he SAW that thing I
described right there with me, and he had no clue either. I just keep
thinking that some people in the navy might be better able to explain it than
most, especially if they have a strong science or engineering background.
Lostgallifreyan
Interesting. I guess fabrication accuracy and timing accuracy improvements
led to its sharp cutoff and improved ability. I'm using one in some project I
have on hold, a way to get pitched sounds to control MIDI signals for musical
instrument control. I'll stop that line of thought there though, I'm not
ready to go into that project for a while.
Richard Clark
<no-...@nowhere.net> wrote:
>If you look at that PDF you'll see the 15' whip antenna is directly connected
>to ground through 80 turns of wire on a ferrite toroid. I might add a spark
>gap in parallel as that wire is not a high current path. So long as it is
>much more likely to go to ground rather than along the line in to the house,
>I'll have done what I'm supposed to do. The trouble would only exist (other
>than unpreventable natural excesses) if it were evident that I had not done
>this.
Yes, it is a grounded design. The folded monopole is simpler, however
and you can deal with matching identically. 80 turns of wire on a
ferrite toroid is going to test the limits of self-resonance, poor Q,
and efficiency across so large a span of frequency.
>Well, a ground rod isn't going to cost much, and making and breaking
>connections to it is one of the easiest and cheapest things I'll be able to
>do, so I'll test that empirically when I'm ready. I won't try to predict it
>now. Whenever I find some new ground noise problem in anything I do here, I
>usually manage to isolate it and solve it acceptably within an hour or less,
>so I'll trust my chances. Usually the purpose hasn't been for RF, but quite
>often the sources did involve RF too so my instincts might help me more than
>my knowledge.
Sounds like a lot of faith and work that will eventually require more
investment in faith and work. A shallow buried radial system would
puncture these superstitions.
>>Let's revisit one of your statements above:
>>>balanced microphone cable with a screen grounded at one end
>> Which end? Any choice stands an equal chance of being the wrong
>> choice.
>>
>
>Well, I did think of that. :) And I didn't state it because I didn't know for
>sure.
That's why I tossed that hand grenade into the mix.
>As I imagine that local RF couplings from various digital devices might
>place small currents on the local ground, I imagine that grounding a shield
>at the remote ground makes sense.
It does, but that isn't the complete solution if you don't choke the
feedline. Again, ground is not found in the rod you drive into the
earth (which, by the way, will take years to "cure" to the ground
resistance you hope to achieve).
>Doesn't matter to me though. It's far
>easier and faster to experiment than to try to predict because there are only
>two ways to try.
This is about experience. You will find (and I have found) damn
little reference to grounding by connection to the earth. It has
taken me years to accumulate these rare references. They have been
topics of discussion here (use google to search the archives).
>Dallas Lankford directly states that no shield is even
>required, and I doubt he'd have said that if he couldn't demonstrate it, and
>as that line is a two-wire loop that has no direct contact with anything, it
>should reject any common mode noise that hits it.
Many people make direct statements (hard not to in this environment
that relies on textual postings). You need to find a better source of
study material as it relates to Common Mode. Twin line suffers it
equally. Again, all such discussion arrives through where the source
and load are, not in the line between.
>Even in audio this matters
>because the same method is used to reject RF pickup on audio lines. I think
>some people persist in baluns instead of op-amp common mode rejection specs
>for this reason, despite the chances of modest distortion in audio bands from
>the transformers used. Not entirely relevant but it illustrates how people
>can find themselves choosing between two less-than-ideal circumstances for
>best effect.
You are confusing topics here. BalUns and what are properly chokes
are not always the same, although their discussion is often co-mingled
to considerable misunderstanding. BalUns are NOT transformers as you
might imagine from the point of view of AF. It is regrettable that
BalUns are called transformers, as their full nomenclature is
Transmission Line Transformer - meaning the transform of Z by
transmission lines that have their ends isolated through choking
action.
Lest that sound too obtuse: The best BalUns do not operate through
magnetic flux linkage. You are not in Kansas anymore.
>I understand that noise context matters for a real attempt to plan for it,
>but that's far more difficult that presenting the basic antenna scheme.
Hence the novelty of individual threads. Noise arrives in the same
manner as RF - it is indistinguishable until you put on your
headphones. Noise is what arrives between your ears.
In regards to this last epithet, I noticed that Lankford wrote a piece
about quad detectors. I first designed one 40 years ago and the
critical component missing in Lankford's discussion (and probably from
many such discussions surrounding this method of detection) is that
the two channel output of a phase quadrature detector is meant to
drive STEREO headphones so that the last step of detection is found in
the brain's capacity to differentiate noise from signal.
Richard Clark
Well, I'm not sure what you are trying to bring up here. As far as
I'm concerned, any topic is open for discussion. If others fume and
fulminate about this being an antenna group, I can easily turn the
discussion into one that is antenna specific.
What did your Dad see? (We used to joke that after the Pueblo
incident they put Marine guards outside of the radio shack for
security. If the ship was in danger of being boarded they were to
step into the shack and shoot the operators. Then I went into the
submarine navy, aboard a tender, the USS Holland, AS-32. We had an
escort sub that followed us at sea - to sink us if the Ruskies got too
close. Ah, the humor of those days.)
Lostgallifreyan
> On Sun, 03 Jan 2010 13:07:26 -0600, Lostgallifreyan
> <no-...@nowhere.net> wrote:
>
>>If you look at that PDF you'll see the 15' whip antenna is directly
>>connected to ground through 80 turns of wire on a ferrite toroid. I
>>might add a spark gap in parallel as that wire is not a high current
>>path. So long as it is much more likely to go to ground rather than
>>along the line in to the house, I'll have done what I'm supposed to do.
>>The trouble would only exist (other than unpreventable natural excesses)
>>if it were evident that I had not done this.
>
> Yes, it is a grounded design. The folded monopole is simpler, however
> and you can deal with matching identically. 80 turns of wire on a
> ferrite toroid is going to test the limits of self-resonance, poor Q,
> and efficiency across so large a span of frequency.
>
Ok, I'll definitely extend reaserch to cover folded monopoles. (Another
curious term given that there has to be some kind of polarity there, but
never mind..) I'll be making by own transformers and housings so I don't mind
plenty of messing around with those.
> Sounds like a lot of faith and work that will eventually require more
> investment in faith and work. A shallow buried radial system would
> puncture these superstitions.
>
The yard out there is partially covered by most of the trunk of a large
felled lime tree, along with lots of branch logs, as part of an effort to
retain nutrients on land that is part of a limited strategy to preserve
wildlife in an urban district. Burying anything out there is harder work than
sinking a ground rod. :) I think I'm going to have to take my chances.
>>>Let's revisit one of your statements above:
>>>>balanced microphone cable with a screen grounded at one end
>>> Which end? Any choice stands an equal chance of being the wrong
>>> choice.
>>>
>>
>>Well, I did think of that. :) And I didn't state it because I didn't
>>know for sure.
>
> That's why I tossed that hand grenade into the mix.
>
>>As I imagine that local RF couplings from various digital devices might
>>place small currents on the local ground, I imagine that grounding a
>>shield at the remote ground makes sense.
>
> It does, but that isn't the complete solution if you don't choke the
> feedline. Again, ground is not found in the rod you drive into the
> earth (which, by the way, will take years to "cure" to the ground
> resistance you hope to achieve).
>
Even if I add a little salt water or dilute acid to accelerate that? This is
something I've been considering.. By choking the feedline, do you mean
placing ferrite slugs round it like those used on VDU cables? That's
something else that will be cheap and easy to test empirically.
>>Doesn't matter to me though. It's far
>>easier and faster to experiment than to try to predict because there are
>>only two ways to try.
>
> This is about experience. You will find (and I have found) damn
> little reference to grounding by connection to the earth. It has
> taken me years to accumulate these rare references. They have been
> topics of discussion here (use google to search the archives).
>
I'll do that. I gravited to Usenet for exactly this reason, I already
collected a few rare sources of info this way in other matters. A lot of the
best stuff is in web archives of usenet posts. (Although for audio I found a
single magazine called Sound On Sound to deal with it efficiently. Not RF,
but it's not exactly far removed technology). I think a lot of good
references just never reached the net, except via postings by people who have
read them. or if they have, they're in university archives I can't reach
anyway.
>>Dallas Lankford directly states that no shield is even
>>required, and I doubt he'd have said that if he couldn't demonstrate it,
>>and as that line is a two-wire loop that has no direct contact with
>>anything, it should reject any common mode noise that hits it.
>
> Many people make direct statements (hard not to in this environment
> that relies on textual postings). You need to find a better source of
> study material as it relates to Common Mode. Twin line suffers it
> equally. Again, all such discussion arrives through where the source
> and load are, not in the line between.
>
There looks like one difference. Any signal hitting a coax screen if used in
this scheme will have a corresponding return current in the core wire, but if
there is any frequency dependent effect based on the nature of the coax
braid's dimensions or in the difference between that and those of the core
wire, then complexites beyond my ken might result (and maybe just as likely
be insignificant). The equality of nature in each half of a twin wire appeals
to me, so long as it actually works. Should be cheap and easy to test that
one...
>>Even in audio this matters
>>because the same method is used to reject RF pickup on audio lines. I
>>think some people persist in baluns instead of op-amp common mode
>>rejection specs for this reason, despite the chances of modest
>>distortion in audio bands from the transformers used. Not entirely
>>relevant but it illustrates how people can find themselves choosing
>>between two less-than-ideal circumstances for best effect.
>
> You are confusing topics here. BalUns and what are properly chokes
> are not always the same, although their discussion is often co-mingled
> to considerable misunderstanding. BalUns are NOT transformers as you
> might imagine from the point of view of AF. It is regrettable that
> BalUns are called transformers, as their full nomenclature is
> Transmission Line Transformer - meaning the transform of Z by
> transmission lines that have their ends isolated through choking
> action.
>
Very likely I am missing plenty. Thing is, I see an unbalanced antenna-to-
ground on one winding and an isolated and balanced line that loops back on
itself carrying induced current from the other. It seems to me that balun and
transformer are terms that apply equally there. In other words, it appears
that the distinctions are neatly avoided while I am directed to exploit the
common nature of the thing being used. Once I see if it works my interest
will grow and I'll explore it further.
> Lest that sound too obtuse: The best BalUns do not operate through
> magnetic flux linkage. You are not in Kansas anymore.
>
>>I understand that noise context matters for a real attempt to plan for
>>it, but that's far more difficult that presenting the basic antenna
>>scheme.
>
> Hence the novelty of individual threads. Noise arrives in the same
> manner as RF - it is indistinguishable until you put on your
> headphones. Noise is what arrives between your ears.
>
That's actually the single best argument for empirical testing. :) Something
else that audio work has told me many times...
> In regards to this last epithet, I noticed that Lankford wrote a piece
> about quad detectors. I first designed one 40 years ago and the
> critical component missing in Lankford's discussion (and probably from
> many such discussions surrounding this method of detection) is that
> the two channel output of a phase quadrature detector is meant to
> drive STEREO headphones so that the last step of detection is found in
> the brain's capacity to differentiate noise from signal.
>
That's interesting. I've considered exploiting that idea before now. Not in
much detail, just in principle because I've heard sounds that needed this to
resolve them.
Lostgallifreyan
Antennas? In this case you'd have your work cut out for you. :) Wasn't just
him who saw it. I saw it first, for an hour and a half, before I decided it
would stick around long enough to justify getting my parents to look at it
too. I'm a bit embarrssed to mention it here other than to point to it there,
but it was two crossed 'beams' in the sky. Trust me, it's hell of a
misdirection if you're not up for it, you'd have to go to alt.lasers and take
a shufti at the posts there.. But I agree, opening it to discussion is good.
I spend about 99.999999% of the time keeping it to myself but I'm getting too
old to want to leave it as unresolved as it is now. If it has to be, ok, but
I ought to try..
Submarines? Those scare me. I never had to go in one, I don't know if
claustrophobia would have beaten me. I have found the sound of water passing
all round me as I waited for sleep in a crew cabin below decks in a ship's
bow to be one of the most comforting sounds I ever knew, so maybe I wouldn't
have.
Richard Clark
<no-...@nowhere.net> wrote:
>Burying anything out there is harder work than
>sinking a ground rod. :) I think I'm going to have to take my chances.
Consider the significance of "shallow" inches, not feet; and sometimes
barely beneath the surface if you have to. If you don't have to (no
trip hazards to worry about) on the surface is equally suitable. You
don't need bare wire, but you can use it - it doesn't matter.
Radials need only be as long as your vertical is high. 16 to a couple
of dozen are sufficient.
>Even if I add a little salt water or dilute acid to accelerate that? This is
>something I've been considering..
Don't go there. Curing takes years and is an issue of soil
compaction.
>By choking the feedline, do you mean
>placing ferrite slugs round it like those used on VDU cables? That's
>something else that will be cheap and easy to test empirically.
That is exactly one very good solution. You need to research the
appropriate ferrite mix which is frequency specific when we are
talking about huge swaths of LF to HF coverage.
>There looks like one difference. Any signal hitting a coax screen if used in
>this scheme will have a corresponding return current in the core wire,
This one statement exposes a very large problem in understanding about
the physics of coaxial cable.
>The equality of nature in each half of a twin wire appeals
>to me, so long as it actually works. Should be cheap and easy to test that
>one...
Actually, it is harder than you might imagine at first glance. Yes,
the methods are simple, but getting past preconceived notions is the
single greatest hurdle. Many engineers are ill suited to the task.
Lostgallifreyan
> On Sun, 03 Jan 2010 14:19:05 -0600, Lostgallifreyan
> <no-...@nowhere.net> wrote:
>
>>Burying anything out there is harder work than
>>sinking a ground rod. :) I think I'm going to have to take my chances.
>
> Consider the significance of "shallow" inches, not feet; and sometimes
> barely beneath the surface if you have to. If you don't have to (no
> trip hazards to worry about) on the surface is equally suitable. You
> don't need bare wire, but you can use it - it doesn't matter.
>
> Radials need only be as long as your vertical is high. 16 to a couple
> of dozen are sufficient.
>
I won't have scope for that much but I can certainly run a few longer ones on
unpaved ground alongside walls if that helps. I've thought about doing that
anyway.
>>Even if I add a little salt water or dilute acid to accelerate that?
>>This is something I've been considering..
>
> Don't go there. Curing takes years and is an issue of soil
> compaction.
>
Ok. I intend to use one of those drills that have a hammer action without
runing, to push the rod in. If I find a rod with a slight taper that would
help.
>>By choking the feedline, do you mean
>>placing ferrite slugs round it like those used on VDU cables? That's
>>something else that will be cheap and easy to test empirically.
>
> That is exactly one very good solution. You need to research the
> appropriate ferrite mix which is frequency specific when we are
> talking about huge swaths of LF to HF coverage.
>
I will, I've already been looking into that so I don't have to blindly hunt
for some toroid by make and model number.. I notice the US has much easier
access to high permeability materials than the UK does, but no idea why this
is so. I saved a couple of PDF's with tables of frequency ranges vs materials
used.
>>There looks like one difference. Any signal hitting a coax screen if
>>used in this scheme will have a corresponding return current in the core
>>wire,
>
> This one statement exposes a very large problem in understanding about
> the physics of coaxial cable.
>
>>The equality of nature in each half of a twin wire appeals
>>to me, so long as it actually works. Should be cheap and easy to test
>>that one...
>
> Actually, it is harder than you might imagine at first glance. Yes,
> the methods are simple, but getting past preconceived notions is the
> single greatest hurdle. Many engineers are ill suited to the task.
>
Try me. All it needs is a clear statement that I can relate to something
I've already experienced. I'm well used to being cautious about what I learn.
Unless it's as tough as atomic physics, it should be digestible, even if
slowly. And I won't be able to taste it till tomorrow... got to sleep soon.
Thanks for this, it encourages me to take the time when others do.
Richard Clark
<no-...@nowhere.net> wrote:
>> Actually, it is harder than you might imagine at first glance. Yes,
>> the methods are simple, but getting past preconceived notions is the
>> single greatest hurdle. Many engineers are ill suited to the task.
>>
>
>Try me. All it needs is a clear statement that I can relate to something
>I've already experienced. I'm well used to being cautious about what I learn.
>Unless it's as tough as atomic physics, it should be digestible, even if
>slowly. And I won't be able to taste it till tomorrow... got to sleep soon.
>Thanks for this, it encourages me to take the time when others do.
We shall proceed with a object lesson found in Fig. 5 of:
http://www.kongsfjord.no/dl/Amplifiers/Common%20Base%20Transformer%20Feedback%20Norton%20Amplifiers.pdf
Consider that this is described in the right side of Fig. 2 with all
the expectations of being "balanced." It is not. Even on viewing the
rough block diagram of Fig. 2 it is apparent in this lack of balance.
Fig. 5 and photos do nothing but support this shortfall.
At first glance, it seems as though these materials are classic text
book stuff that begs to be accepted as "balanced;" reality intrudes in
that RF (far more so than AF) finds interwinding capacitance is not
distributed equally for T2 and T3 primaries to secondaries.
The input/output windings are easily as unbalanced as one could find.
"Of Course! a protest might start. T2 is meant to support an
unbalanced input." However, a closer glance would admit that the
capacitive coupling from the top of T2 input to the top of T2 output
is NOT the same as the capacitive coupling from the bottom of T2 input
to the bottom of T2 output (irrespective of the implied ground
connecting, or not, to the middle of the T2 output winding).
The top Basic Amp is thus presented with a higher potential than the
lower Basic Amp. One might protest that this does not matter as T3
uncouples the two to present a new output through it to the 50 Ohm
output. My rejoinder would be "What practical advantage is then found
in the symmetry of upper/lower Basic Amps?" I would then point out
that the Common Modality present in the input, is amplified in the
upper half and finds its way through the system.
The solution involves complex winding taps with capacitors tied from
them to common to enforce a balance. This is not practiced
(obviously) in the object lesson presented at the page referenced
above.
A protest might erupt that this example's capacitive asymmetry only
admits of a very small imbalance. I would respond that Common
Modalities may easily support considerable currents/voltages that when
reduced through divider action are easily in excess of small signals
of interest. The Basic Amp input Z is 50 Ohms; an imbalance in the
interwinding coupling capacitance amounting to 50 KOhms will add 1000
microvolts for any 1V CM signal on the left. At 1MHz, this 50 KOhms
would be a capacitance imbalance of 3 pF. Looking at the wire
dressing of the coils in the photo would suggest 3 times this easily
(and no attention has been paid to this at all). Now extrapolate to
the 31 Meter band.... Could your AGC tolerate the local AM station's
10,000 microvolt leakage sitting on top of Radio Burundi's signal?
Grounding and shielding is not a simple topic although it is deceptive
in appearance.
Lostgallifreyan
> At 1MHz, this 50 KOhms
> would be a capacitance imbalance of 3 pF. Looking at the wire
> dressing of the coils in the photo would suggest 3 times this easily
> (and no attention has been paid to this at all).
That's the bit that seems most important, and I can also relate to it. It
doesn't take much to cause a few pF difference.
A few points occur to me though...
First, to get it out of the way.. if this was causing serious bother, which
it surely might if it is that bad at the lowest end of the SW range, what on
earth induces a designer to persist in thinking it's working? Either it
isn't, and he's deluded; or it is, so why?
Second, I imagined balance to pretty much relate to symmetry. I hadn't seen
that file yet (even though I'd actually grabbed it with intent to), and the
looseness of the coil wiring isn't lost on me. My idea was to omit the amps
and just wind the toroids with neat symmetry to reduce obvious causes of
imbalance and take it from there. If it works, I use it, if not, I try
something else. Given that I have more than once been told that I might
overdrive the input on the ATS-909 radio with a 18' whip in the back yard, I
decided that I might as well omit the amps as they only boost a few dB, and
instead rely initially on the built in attenuator for first efforts to see
what's out there, then consider building (or getting lucky with on eBay) a
preselecting filter on the input.
Third, the amount of effect a few pF has on a circuit would depend also on
the inductance, or resistance, or any delay in the circuit. I hadn't looked
closely at that (I'd want to see what happened with a simple test first), but
I am guessing that the simpler idea of a twin wire with transformers and no
amps would have a smaller risk of imbalanced signals, so a better common mode
rejection. Why not do the amplification after the second transformer where
balance is clearly irrelevant, if it has to be done at all?
I may still be missing something other than a grasp of quantities, but
whatever I do, it has to be something that aims to do what that scheme was
said to be able to do. I don't have a lot of space, and that radio ideally
needs a single antenna to cover all of its AM range, at least for initial
efforts. Ideally some scheme that can be improved rather than thrown out when
I need something better.
Lostgallifreyan
> At 1MHz, this 50 KOhms
> would be a capacitance imbalance of 3 pF. Looking at the wire
> dressing of the coils in the photo would suggest 3 times this easily
> (and no attention has been paid to this at all).
That's the bit that seems most important, and I can also relate to it. It
Roy Lewallen
> . . .
> Second, I imagined balance to pretty much relate to symmetry. . .
You might find this interesting:
http://eznec.com/Amateur/Articles/Baluns.pdf.
Roy Lewallen, W7EL
Richard Clark
<no-...@nowhere.net> wrote:
>Richard Clark <kb7...@comcast.net> wrote in
>news:3ni2k51p7dc549v5q...@4ax.com:
>
>> At 1MHz, this 50 KOhms
>> would be a capacitance imbalance of 3 pF. Looking at the wire
>> dressing of the coils in the photo would suggest 3 times this easily
>> (and no attention has been paid to this at all).
>
>That's the bit that seems most important, and I can also relate to it. It
>doesn't take much to cause a few pF difference.
>
>A few points occur to me though...
>
>First, to get it out of the way.. if this was causing serious bother, which
>it surely might if it is that bad at the lowest end of the SW range, what on
>earth induces a designer to persist in thinking it's working? Either it
>isn't, and he's deluded; or it is, so why?
That is answered rather simply: isolated experience. Having solved a
problem for single application does not make it a universal solution -
it is a good start however. For instance (as to this issue of
isolation), these designs were originally intended for lowfers where
this coupling would have been decimated (its impact reduced by 10).
Spinning out the same "successful" design to 10MHz without
consideration for this one issue I've pointed out would bring the user
to their knees: "I've tried everything and I still get this
interference!" Well, the user has not tried everything; it was simply
the right design in the wrong application which with a bit of effort
could be improved dramatically. Many of the layout and design
considerations for the lowfers are commendable and easily applicable
into the VHF. A VHF designer would have chosen other input topologies
is all.
In a sense, the VHF designer is also suspect for having an isolated
experience. Practical solutions are not always scaleable.
As I pointed out, very few changes are necessary and there is even a
simpler solution. You can shield the primaries from the secondaries
(kills the capacitive link). Unfortunately this brings a new problem:
where do you tie the new shield to? The wrong choice will actually
inflate the problem. As I said, this is not a simple field where
there are nesting layers of shields and broken shields with
non-contacting overlaps. Which one overlaps the other can bring
success or misery.
>Second, I imagined balance to pretty much relate to symmetry. I hadn't seen
>that file yet (even though I'd actually grabbed it with intent to), and the
>looseness of the coil wiring isn't lost on me. My idea was to omit the amps
>and just wind the toroids with neat symmetry to reduce obvious causes of
>imbalance and take it from there. If it works, I use it, if not, I try
>something else.
Well, here the topology you describe will carry the common mode
directly through (with some attenuation) as it is inherently out of
balance when the input primary's capacitive coupling is out of whack.
This is why I harp on "first principles." The amps have nothing to do
with the problem, they simply help illustrate the imbalance.
As to you "giving it a try" returns us to the heavily qualified
"success" of isolation. You could easily connect your antenna
barefoot to your receiver and experience no problems at all! This
does not constitute your "solution" as being universal. When you move
and try your "solution" again, it could easily fail for not observing
first principles.
However, this is not to impede you from simply getting on with it. The
hallmark of becoming successful is failing as many times as you can.
>Given that I have more than once been told that I might
>overdrive the input on the ATS-909 radio with a 18' whip in the back yard, I
>decided that I might as well omit the amps as they only boost a few dB, and
>instead rely initially on the built in attenuator for first efforts to see
>what's out there, then consider building (or getting lucky with on eBay) a
>preselecting filter on the input.
Ham radio was invented on a bread board. You need one coil
(selectable) and two variable capacitors that can be scavenged from
very, very old table top radios. You would spend more in shipping for
a "preselector" than what you would pay at the nearest junk store for
these three items. Someone who had to pinch pennies would do it with
one cap and one coil and a lot of alligator jumpers. Even this
solution can be made elegant and occupy a space no larger than a
pocket sized notebook. If you robbed these componets from very, very
old transistor radios, you could build it in a mint tin.
>Third, the amount of effect a few pF has on a circuit would depend also on
>the inductance, or resistance, or any delay in the circuit. I hadn't looked
>closely at that (I'd want to see what happened with a simple test first), but
>I am guessing that the simpler idea of a twin wire with transformers and no
>amps would have a smaller risk of imbalanced signals, so a better common mode
>rejection. Why not do the amplification after the second transformer where
>balance is clearly irrelevant, if it has to be done at all?
As I said, the problem is in the topology, not the amplifiers.
>I may still be missing something other than a grasp of quantities, but
>whatever I do, it has to be something that aims to do what that scheme was
>said to be able to do. I don't have a lot of space, and that radio ideally
>needs a single antenna to cover all of its AM range, at least for initial
>efforts. Ideally some scheme that can be improved rather than thrown out when
>I need something better.
You have barely nicked the surface of possibility in discussion here.
Loop antennas (which can be truly balanced and passed through coax)
are a natural answer for a lot of the spectrum you want to listen to.
In fact, "shielded loops" are explicitly coaxial and extremely simple
to construct (although many web sources describe them incorrectly).
They exhibit very sharp nulls (when that matters), and you can lay
them over 90 degrees to make them vertically polarized (and then use
them in phased configurations for beam steering).
Lostgallifreyan
dnX6Mt9DKqd_Wn...@giganews.com:
Thanks, it is. I read the first part that covered the way RF current can flow
on the outside of a coax, and how the same effect (though as you say, hard to
visualise) occurs in a twin feed line. I see how it applies to the ferrite
'slugs' I shall try once I set something up, though I skipped most of the
stuff on the voltage balun. The current balun made more sense to me right
away.
Note that the idea that has caught my attention is to use transformers..
there would be no direct current contact between either the line and the
antenna, or the line and the receiver. This isn't my own idea, it's just a
wheeze that looks most interesting because it looks like it ought to work,
and if it does it certainly pretects the receiver input rather well. It's
beginning to look as if choosing coax or twin line isn't so important as
knowing if that transformer scheme is valid, so long as I do something to
block common mode currents with a choke balun on the line.
Lostgallifreyan
Ok, I see that isolated experience can be a problem. As far as I can see
there will be a level of complexity best averted by empirical testing, so
long as I don't miss something really fundamental. Which I am trying not to
do.. I found a USMC guide to RF and antenna selection, a 5MB PDF file, that
has a Marine's habit of cutting to the chase, it looks like I found a good
guide there.
http://www.armymars.net/ArmyMARS/Antennas/Resources/usmc-antenna-hb.pdf
The topolgy I describe WILL carry imbalance through, I know. :) I thought it
might at least be a start if it didn't add any of its own. I realise you were
using the amps as an illustration of how imbalance can arise between those
toroids, I was thinking that fewer parts means less to go wrong. Precise
symmetry in topology might be a lot easier if I didn't have to use those.
Again, I wonder why they're even there. Isn't it easier to put a gain stage
after the second toroid?
Point taken on the costs of the selector. It was a long time ago, but I think
I saw something intended to do this task, a design that built it from wire
wound on a bit of plastic water pipe or something. I started Googling for
designs earlier but got waylaid. One bit of waylaying involved a remark that
tuning might offer more problems that a fixed narrowband filter, but so
little context was offered that I don't know how to judge the remark.
If I put up conspicuous loops here I might get people bothering me about
planning permission or some other means of negative compulsion. :) If I can
do this with a vertical whip it will be much less awkward.
Richard Clark
<no-...@nowhere.net> wrote:
>Again, I wonder why they're even there. Isn't it easier to put a gain stage
>after the second toroid?
A circuit serves more purposes than gain. Of course, the simple
circuitry found in the file we are discussing has limited offerings.
Of what is offered is controlling input and output Z which is not a
trivial matter.
My preference is found in using Operational Amplifiers instead of
discrete transistors. There is more design flexibility and more
purposes may be served. OpAmps will control input and output Z with
far more rigidity (it is very difficult for externalities to shift
these parameters making for a rock solid design). OpAmps will also
preserve fidelity (faithful phase, magnitude) and not introduce any
distortion, and will drive out noise not already in the signal. Other
advantages can be obtained, but this is enough.
>If I put up conspicuous loops here I might get people bothering me about
>planning permission or some other means of negative compulsion. :) If I can
>do this with a vertical whip it will be much less awkward.
Practicality needs to be served too. Loops can be useful indoors as
well, and they needn't fill a room. They will test the limits of
balance with the nearby clutter - an opportunity to turn your
environment into an RF lab.
Roy Lewallen
> . . .
> there would be no direct current contact between either the line and the
> antenna, or the line and the receiver. This isn't my own idea, it's just a
> wheeze that looks most interesting because it looks like it ought to work,
> and if it does it certainly pretects the receiver input rather well. It's
> beginning to look as if choosing coax or twin line isn't so important as
> knowing if that transformer scheme is valid, so long as I do something to
> block common mode currents with a choke balun on the line.
An ideal transformer will effect perfect current balance. What I don't
know, and have never seen any theoretical or experimental work on, is
how effective a real physical transformer can be made to be in that
regard. There will be capacitive coupling between windings which could
be a source of common mode current (current imbalance), and it might be
necessary to take some or a lot of care in the winding to maintain good
balance. And of course the system will have the windings' impedance
between the conductors, necessitating care in transformer design for
that reason. A fundamental advantage of the balun type connection is
that the balance improves as the winding coupling becomes more intimate,
while that tends to work against a conventional transformer. It would be
an interesting study -- I regret I don't have the time to dig into it more.
Roy Lewallen, W7EL
Lostgallifreyan
I'll give it a go, though I don't know if what I try will have enough rigour
to give useful results back. I just sent a cheque for some FT114-43 toroids
which are big enough to consider a screen between windings, though as Richard
Clarke said, it might be awkward finding the best point to tie that screen
to. Re impedance of windings, I have no idea or plan except to aim for close
spacing (within each coil) and neat symmetry, and glue to keep them in place
so that whatever results it remains steady.
Lostgallifreyan
> On Mon, 04 Jan 2010 14:44:31 -0600, Lostgallifreyan
> <no-...@nowhere.net> wrote:
>
>>Again, I wonder why they're even there. Isn't it easier to put a gain
>>stage after the second toroid?
>
> A circuit serves more purposes than gain. Of course, the simple
> circuitry found in the file we are discussing has limited offerings.
> Of what is offered is controlling input and output Z which is not a
> trivial matter.
>
> My preference is found in using Operational Amplifiers instead of
> discrete transistors. There is more design flexibility and more
> purposes may be served. OpAmps will control input and output Z with
> far more rigidity (it is very difficult for externalities to shift
> these parameters making for a rock solid design). OpAmps will also
> preserve fidelity (faithful phase, magnitude) and not introduce any
> distortion, and will drive out noise not already in the signal. Other
> advantages can be obtained, but this is enough.
>
I really like op-amps too, they have often made my life easier. Not used them
in RF though, just audio and modest DC instrumentation designs of my own..
About those amps in that scheme, I think I didn't grasp what they were doing,
other than gain, because I assumed the idea of balancing implied by the
design would be central whether they were used or not. It still seems to me
that if the line worked without them, then a single stage could be applied
after the signal passed to the unbalanced input after the second toroid. If
not (as in not possible as opposed to merely awkward), then I'm still missing
something.
>>If I put up conspicuous loops here I might get people bothering me about
>>planning permission or some other means of negative compulsion. :) If I
>>can do this with a vertical whip it will be much less awkward.
>
> Practicality needs to be served too. Loops can be useful indoors as
> well, and they needn't fill a room. They will test the limits of
> balance with the nearby clutter - an opportunity to turn your
> environment into an RF lab.
>
> 73's
> Richard Clark, KB7QHC
>
I'll definitely read up on loops. (Been reading the first of two USMC radio
handbooks today, second is an update of the one I found yesterday. No loops
mentioned in first, but the second is specific to antennas. Both guides are
quickly filling forgotten gaps in what I knew, plus showing me plenty I
didn't).
Btw, how critical is the resistance of wire in a few ground radials? I have
some thin stainless steel wire that would be strong and enduring out there
but at around 1.5 ohms or more per 6 inches I can't help thinking that's too
much. I like the idea though, because clamping ends of it very firmly between
copper washers could be fast and easy for good and reliable contact.
Richard Clark
<no-...@nowhere.net> wrote:
>Btw, how critical is the resistance of wire in a few ground radials? I have
>some thin stainless steel wire that would be strong and enduring out there
>but at around 1.5 ohms or more per 6 inches I can't help thinking that's too
>much. I like the idea though, because clamping ends of it very firmly between
>copper washers could be fast and easy for good and reliable contact.
The stainless steel is a non-starter. Use more radials of wire-wrap
wire if you are concerned about visibility vs. thickness.
Vegetation/grass will quickly bury most wire when Spring comes (and
possibly before). Grass will be so tenacious that even mowing the
lawn will not bring it up (unless you have a thatching attachment).
Lostgallifreyan
Ok, copper's no problem, was just wondering about stuff I had plenty of at
hand.. I wish I had a lawn. :) I was thinking that it would be an ideal
method. My main difficulty (apart from a large amount of heavy logs (and most
of a tree trunk) is that the best place to mount the antenna is in a far
coner of a plot so I can't lay radials all round it. I can probably get the
permission of one neighbour to run a ground wire along the far end of his
garden along a low wall, but that same wall is a high wall on the other side,
there's a drop of several feet as well as no chance of permission to lay
wires there. This is why I'll want a ground rod, as a tree used to grow
there, the rotted roots might be my best chance of anything like a conductive
network that is close to the surface, in addition to a few ground wires. I'm
a tenant, I don't own the land, and can't do much except work round what is
there.
Lostgallifreyan
news:Xns9CF7BE6C58A...@216.196.109.145:
Thinking about what I read recently, it seems that if the whip is not
vertical but slightly leaning back over the plot of land toward the houses,
it will have a better chance of using the sky waves, but what I don't know is
whether that demands ground radials to be biased (if biased at all) to favour
coverage on the side the antenna is leaning over, or the other side. My guess
is the side it's leaning over... Is this true? If so, it will help a lot to
make the best of that space.
Richard Clark
<no-...@nowhere.net> wrote:
>> Ok, copper's no problem, was just wondering about stuff I had plenty of
>> at hand.. I wish I had a lawn. :) I was thinking that it would be an
>> ideal method. My main difficulty (apart from a large amount of heavy
>> logs (and most of a tree trunk) is that the best place to mount the
>> antenna is in a far coner of a plot so I can't lay radials all round it.
Running a fan of 90 degrees is fine, there's nothing exact about this
except for those who imagine they will suffer the dB of
out-of-symmetry.
>> I can probably get the permission of one neighbour to run a ground wire
>> along the far end of his garden along a low wall, but that same wall is
>> a high wall on the other side, there's a drop of several feet as well as
>> no chance of permission to lay wires there.
Don't bother. It isn't worth anyone's effort or intrusion.
>>This is why I'll want a
>> ground rod, as a tree used to grow there, the rotted roots might be my
>> best chance of anything like a conductive network that is close to the
>> surface, in addition to a few ground wires.
A wire mesh or mat (like chicken coop wire) over the surface of that
area would serve far better. That doesn't sound like an option so the
matter of pursuing conductivity of rotted roots is an illusion.
>>I'm a tenant, I don't own
>> the land, and can't do much except work round what is there.
You'll be able to do enough without much impact.
>>
>
>Thinking about what I read recently, it seems that if the whip is not
>vertical but slightly leaning back over the plot of land toward the houses,
>it will have a better chance of using the sky waves, but what I don't know is
>whether that demands ground radials to be biased (if biased at all) to favour
>coverage on the side the antenna is leaning over, or the other side. My guess
>is the side it's leaning over... Is this true? If so, it will help a lot to
>make the best of that space.
Your gain/loss advantage will be in the direction from the antenna
base out along of the middle radial in a 90 degree fan. Leaning won't
significantly alter things for a very short antenna (in terms of
wavelength).
Now as to these advantages and disadvantages. Once you get to a
minimun set of radials (call it four), the addition of more wire won't
budge your S-Meter more than a needle width (and that is being
generous). The addition of more radials concerns establishing a firm
reference of ground for Z.
Lostgallifreyan
Thankyou. This is good, it sounds like the basic plan will work then, and I
might be able to get some chicken wire to cover at least part of it. One
possible complication I didn't mention is that the intended mounting point is
at a T junction of three wire mesh fences of equal height, about 6'. They
don't have very reliable conductivity between each zigzag strand (oriented
vertical) as at least one fence has a green plastic coating on its wires. I
intend mounting the whip on a concrete post at the junction of these fences.
I imagine the fences will raise (and make diffuse) the precise physical level
of the RF ground, but I don't know whether they'll be a serious problem, or
maybe even be helpful. I can try grounding them a bit better, but otherwise
there's not a lot I can do about them.
One other thought... In that USMC antenna manual there is a mention of
something similar, a 15' whip tilted and also tied back so the upper part is
almost horizonatal, it's intended as a way to use short(ish) distances for
skywave propagation. It looks useful given the context of trees and buildings
within 100m of my best mounting point. What I'm not sure of is whether the
curvature of their tied antenna is relevant, or a straight tilted whip would
have no significant differences.
Jim Lux
> Thankyou. This is good, it sounds like the basic plan will work then, and I
> might be able to get some chicken wire to cover at least part of it.
Chicken wire rusts out pretty fast.. You'd probably be better off just
scrounging some AWG20 copper wire and improvising a little grid or
randomly laying it out.
One
> One other thought... In that USMC antenna manual there is a mention of
> something similar, a 15' whip tilted and also tied back so the upper part is
> almost horizonatal, it's intended as a way to use short(ish) distances for
> skywave propagation. It looks useful given the context of trees and buildings
> within 100m of my best mounting point. What I'm not sure of is whether the
> curvature of their tied antenna is relevant, or a straight tilted whip would
> have no significant differences.
Curvature isn't "significant", and for a lot of cases, the tilt isn't
either. But, tying the whip back does keep it from whacking too hard on
low hanging branches.
Richard Clark
<no-...@nowhere.net> wrote:
>Thankyou. This is good, it sounds like the basic plan will work then, and I
>might be able to get some chicken wire to cover at least part of it.
There is a down-side to this and what you have revealed below:
>One
>possible complication I didn't mention is that the intended mounting point is
>at a T junction of three wire mesh fences of equal height, about 6'. They
>don't have very reliable conductivity between each zigzag strand (oriented
>vertical) as at least one fence has a green plastic coating on its wires.
Both the mesh of chicken wire, and the fence crosspoints may suffer
from cross-modulation products due to corrosion at the joints AND if
the metal is galvanized. This is evidenced in a nearby transmitter
(and nearby is relative measure) exciting the wire, and rectifying at
the corroded crosspoints. This rectification creates harmonics and
you are off to the races in terms of spurious frequency generation
across a wide bandwidth.
Oh Brave New World of common mode.
>I
>intend mounting the whip on a concrete post at the junction of these fences.
>I imagine the fences will raise (and make diffuse) the precise physical level
>of the RF ground, but I don't know whether they'll be a serious problem, or
>maybe even be helpful. I can try grounding them a bit better, but otherwise
>there's not a lot I can do about them.
As you describe at least one fence having insulated wire (which is
good from the cross-mod point of view) this makes no difference RF
ground-wise; and being elevated only slightly shifts things.
One exception is found in proximity in that this elevated ground will
indirectly short out the lower section of your vertical. This is more
a matter of Z than sensitivity.
The solution is to elevate your vertical's feedpoint to the height of
the fence top.
>One other thought... In that USMC antenna manual there is a mention of
>something similar, a 15' whip tilted and also tied back so the upper part is
>almost horizonatal, it's intended as a way to use short(ish) distances for
>skywave propagation. It looks useful given the context of trees and buildings
>within 100m of my best mounting point. What I'm not sure of is whether the
>curvature of their tied antenna is relevant, or a straight tilted whip would
>have no significant differences.
Well, what they (or you) call sky wave is properly NVIS (near vertical
incident _____ - I forget the last part) which is meant for local
communications, which is more what the ground forces are interested
in. The Marines in Afghanistan are not going to DX headquarters back
at Pennsylvania Avenue in DC. When I taught VHF/UHF comm in the Navy,
our equipement easily lost 10dB of transmitted/received signal levels
just getting from the shack to the antenna. We didn't care. Push
more power if necessary, as for reception, line of sight was all that
was necessary, and that was to the horizon (no more than 8 or 10
miles). I don't think the government has bought any QRP rigs since
WWII.
In fact, that tilting's mission has also been satisfied with end
loaded dipoles place directly on the ground (which was largely sand).
I and my buddy used one for field day. Another antenna is an
unterminated coax laid across the ground. Both suffer mightily in
efficiency, but they offer ease of construction and purport to enjoy
less noise problems. To this last, most local noise arrives by
vertical polarization, and signals in the sky arrive by elliptical
(both vertical and horizontal by varying degree) polarization. For a
quick and dirty test, I doubt any other test could be quicker to do.
You might want to add a short pig-tail to the unterminated coax.
Further experimentation would be to add 8 to 10 inches of ferrite
beads to the coax, half way back on it toward your shack. This would
snub your home's injection of noise into your receiver (conducting out
from the house on the coax outer shield and folding back at the far
end). The next experiment (if this first proved useful) would be to
add a local ground at the same point and tie it to the shield (after
penetrating the jacket, of course). Yes, this violates some of my
other advice about mixing grounds, but for experiment's sake, it will
add to your repertoire of learning the complexities and benefits of
ground. The purpose of this new ground is to discharge that choked
noise into ground. I have successfully done this to quiet my home's
noise generation as detected in my receivers. The ultimate proof of
this concept is being able to throw the master breaker on your home
and noting any change in the noise floor.
Throwing that breaker is probably at the extreme of your family's
tolerance of your hobby. To this end you want to plan to do it once.
This means doing a noise floor survey at hourly intervals for all
bands and keeping notes for a week or two. Then, one day when there's
the least possibility of disrupting domestic tranquility, throw the
main and do a quick survey again. I have managed to quiet my
receivers by 5 to 10 dB through tests like these.
Buried cable, or ground level run cable can snub local noise induction
too (but it is still a good idea to choke at the feed point if no
where else). This last observation is to inform you that metallic
connection to earth is not always necessary. You should be equally
informed that the proximity of earth can also negatively affect what
positive gains you are seeking too.
Lostgallifreyan
news:hi2gc3$m5r$1...@news.jpl.nasa.gov:
> Lostgallifreyan wrote:
>
>> Thankyou. This is good, it sounds like the basic plan will work then,
>> and I might be able to get some chicken wire to cover at least part of
>> it.
>
> Chicken wire rusts out pretty fast.. You'd probably be better off just
> scrounging some AWG20 copper wire and improvising a little grid or
> randomly laying it out.
>
True. Was just thinking that it's not that hard to find something meshlike so
even if it did it could be replaced for free. Given the price of scrap
copper, that rarely comes free these days. :)
>> One other thought... In that USMC antenna manual there is a mention of
>> something similar, a 15' whip tilted and also tied back so the upper
>> part is almost horizonatal, it's intended as a way to use short(ish)
>> distances for skywave propagation. It looks useful given the context of
>> trees and buildings within 100m of my best mounting point. What I'm not
>> sure of is whether the curvature of their tied antenna is relevant, or
>> a straight tilted whip would have no significant differences.
>
> Curvature isn't "significant", and for a lot of cases, the tilt isn't
> either. But, tying the whip back does keep it from whacking too hard on
> low hanging branches.
>
In the case of a 15' whip, tilt might be. At least, if it isn't I have to
wonder why that USMC antenna manual was suggesting one for short-range
skywave use.
Document is "MCRP 3-40.3c" (PDF) 'Figure 4-34. AN/MRC-138 with NVIS Antenna'.
(About 4/7 of the way through that file, as gauged by scrollbar).
Where I am it seems the best chance due to surrounding buildings, trees,
fences, etc, is to use a slightly less exaggeratedly steep 'view' of the sky
than is implied by that description and drawing. If you look at that drawing
you can see that it isn't done to tie the antenna out of the way. :) There
seems to be specific reason for doing what they do there.
The curvature made me wonder, based on a relector, in an indirect way... I
read that a longer straight isolated rod placed directly behind a whip,
separated by a quarter wavelength, could be a reflector. While I guess any
curvature in either that rod or the whip might be insignificant at low HF, I
inferred that it had to be straight to work efficiently if the whip was
straight. There seemed to be implications that straightness, or lack of it,
mattered. That made me wonder if curvature in a whip (forget the reflector, I
have...) leaning toward a building might very slightly favour pickup on the
convex side and attenuation on the concave side, or have any other mildly
directional benefits. If so it might be a useful part of a strategy to reduce
noise from nearby buildings. Of course it might be useless trying, but it
looks like a nice idea...
Lostgallifreyan
> Well, what they (or you) call sky wave is properly NVIS (near vertical
> incident _____ - I forget the last part)
Skywave. :) At least, according to the document I just mentioned in previous
post. Sorry, I'll get to the detail in your post now..
Lostgallifreyan
> On Wed, 06 Jan 2010 04:18:10 -0600, Lostgallifreyan
> <no-...@nowhere.net> wrote:
>
>>Thankyou. This is good, it sounds like the basic plan will work then,
>>and I might be able to get some chicken wire to cover at least part of
>>it.
>
> There is a down-side to this and what you have revealed below:
>
>>One
>>possible complication I didn't mention is that the intended mounting
>>point is at a T junction of three wire mesh fences of equal height,
>>about 6'. They don't have very reliable conductivity between each zigzag
>>strand (oriented vertical) as at least one fence has a green plastic
>>coating on its wires.
>
> Both the mesh of chicken wire, and the fence crosspoints may suffer
> from cross-modulation products due to corrosion at the joints AND if
> the metal is galvanized. This is evidenced in a nearby transmitter
> (and nearby is relative measure) exciting the wire, and rectifying at
> the corroded crosspoints. This rectification creates harmonics and
> you are off to the races in terms of spurious frequency generation
> across a wide bandwidth.
>
> Oh Brave New World of common mode.
>
Hmm. :) Just going to have to chance that, the bigger fence (main road in T
junction metaphor) is a galvanised type, with plenty of weathering. If I have
patience I might weave in a grounded length of copper wire, but I suspect
more weathering will nullify any useful initial results of that move so I
probably won't.
>>I
>>intend mounting the whip on a concrete post at the junction of these
>>fences. I imagine the fences will raise (and make diffuse) the precise
>>physical level of the RF ground, but I don't know whether they'll be a
>>serious problem, or maybe even be helpful. I can try grounding them a
>>bit better, but otherwise there's not a lot I can do about them.
>
> As you describe at least one fence having insulated wire (which is
> good from the cross-mod point of view) this makes no difference RF
> ground-wise; and being elevated only slightly shifts things.
>
> One exception is found in proximity in that this elevated ground will
> indirectly short out the lower section of your vertical. This is more
> a matter of Z than sensitivity.
>
> The solution is to elevate your vertical's feedpoint to the height of
> the fence top.
>
Oh, it will be. A tad higher, if anything. Just a few inches though, between
bottom end of whip and top of fence.
>>One other thought... In that USMC antenna manual there is a mention of
>>something similar, a 15' whip tilted and also tied back so the upper
>>part is almost horizonatal, it's intended as a way to use short(ish)
>>distances for skywave propagation. It looks useful given the context of
>>trees and buildings within 100m of my best mounting point. What I'm not
>>sure of is whether the curvature of their tied antenna is relevant, or a
>>straight tilted whip would have no significant differences.
>
> Well, what they (or you) call sky wave is properly NVIS (near vertical
> incident _____ - I forget the last part) which is meant for local
> communications, which is more what the ground forces are interested
> in. The Marines in Afghanistan are not going to DX headquarters back
> at Pennsylvania Avenue in DC. When I taught VHF/UHF comm in the Navy,
> our equipement easily lost 10dB of transmitted/received signal levels
> just getting from the shack to the antenna. We didn't care. Push
> more power if necessary, as for reception, line of sight was all that
> was necessary, and that was to the horizon (no more than 8 or 10
> miles). I don't think the government has bought any QRP rigs since
> WWII.
>
I don't have a lot of line of sight.. While I'm not living in a well, that
might be a closer analogy than the terrain most SWL'ers assume they'll find.
I do get a fair chunk of south and western sky though. I figured a scheme
intended to transmit to such a space should receive ok from it. If I try any
other angle I might as well try to hear the local neighbourhood noises, but
getting a sense of what lies beyond all that is why I'm doing this. Maybe
after some initial tries I might have to consider something much more
directional anyway, but hopefully not.
> In fact, that tilting's mission has also been satisfied with end
> loaded dipoles place directly on the ground (which was largely sand).
> I and my buddy used one for field day. Another antenna is an
> unterminated coax laid across the ground. Both suffer mightily in
> efficiency, but they offer ease of construction and purport to enjoy
> less noise problems. To this last, most local noise arrives by
> vertical polarization, and signals in the sky arrive by elliptical
> (both vertical and horizontal by varying degree) polarization. For a
> quick and dirty test, I doubt any other test could be quicker to do.
> You might want to add a short pig-tail to the unterminated coax.
>
An odd idea, but I like it. It might be that in my location some drastic
shifts from convention, to get best SNR never mind losses, then add gain
later, might be best. If something like that worked I'd leave it working.
Ok, I'll be keeping the feed line as mobile as I can, because I already
suspected that position and number of ferrite slugs might be something I want
to change a lot to test. Ultimately I hope I can run it along the top
of one of the chainlink fences. Circuit breakers will be no problem, I live
alone in a basement flat. :)
Richard Clark
<no-...@nowhere.net> wrote:
>> Well, what they (or you) call sky wave is properly NVIS (near vertical
>> incident _____ - I forget the last part)
>
>Skywave. :) At least, according to the document I just mentioned in previous
>post. Sorry, I'll get to the detail in your post now..
Something in the back of mind said it was.