Shortwave random-wire antenna question
Dave
piece of four-stranded wire with alligator clip to the internal "whip"
antenna of my portable shortwave receiver, for the extra performance such a
device offered. It works so well that I now cannot usually use my "DX"
setting because of all the background noise (sounds like hundreds of other
broadcasts vying for attention.) I don't know the frequency source of all
this background noise, but would like to filter out as much of it as I can.
One manufacturer of a similar "wind-up" antenna adds a capacitor to the wire
in order to lower the resonance frequency of the wire. If I were going to
try something similar (adding a capacitor, in series) in an attempt to bring
the resonance of the wire down into the 30 MHz range, what size (roughly)
capacitor should I use? Should I just try a few with different ranges, or
does anyone here have any suggestions?
TIA
Cross-posted between sci.electronics.basics and rec.radio.shortwave
Matt J. McCullar
have noise blanking, AGC, extra RF amplification (which can be bypassed),
frequency shift/width, etc.
Telamon
"Dave" <db5...@hotmail.com> wrote:
Since you have cross posted to sci.electronics.basics lets try to look
at this logically and as non technically as possible.
The are two things that you need to accomplish to hear a station on your
radio in the way of signal strength.
1. The signal must large enough for the radio to amplify it and
reproduce it at the speaker.
2. The signal must be stronger than the noise floor of the radio and any
external noise the antenna picks up by some margin over the station you
want to hear. Usually this is something like 10 dB.
You can't do anything about the noise floor of the radio unless you want
to modify it. The basic sensitivity of the radio is a decision you made
when you bought it.
That leaves the antenna. What you did was to put up the most basic type,
which is called a Marconi or common mode antenna. For a simple antenna
it is about as non-selective as you can make hence the noise level is
high on the radio. Worse you might be over loading the radio and the
radio itself may be generating some of the noise. Portables are designed
to be sensitive and simple so they can't handle much signal. A strong
signal out or in band could be causing you additional trouble.
Whether 36 feet of wire is to much or not depends on where you live but
for most radios generally won't cause the overload problem it's just
that it is picking up everything well including lots of locally
generated noise.
That is the basically where you are at.
What can you do about this. You want to pick up more of the signals
(stations) you want to hear without hearing noise from other electrical
appliances or stuff out of band.
You need a more complex antenna design that will not pick up as much
noise as the signal you want to hear. Noise is on all frequencies and
comes from all directions.
A more complex antenna design can do things like:
1. Limit the direction it picks up signal or noise. You can benefit from
this by pointing the antenna at the signal you want or conversely
attenuating a noise source.
2. Changing the type of energy the antenna picks up. The antenna type
determines whether it picks up common mode or differential mode.
3. The antenna type also determines whether it is sensitive to the
electric, magnetic fields or both.
4. The antenna type also determines the band or bands of frequencies it
will pick up well.
All the above will limit the total amount of noise energy it will
present to the radio so it has less to deal with. Basically you use the
antenna design to preselect the signals you want to pick up. The
downside of this is short wave covers a wide range of frequencies so you
will need more than one antenna. For some type of resonant antenna the
smallest number of antennas you need are two and better would be three.
To get started with a more complex antenna and to see if you are really
improving your reception start with a weak signal using just the radios
whip antenna. Use a station on a high band (smaller antenna) during the
daytime.
Make a simple resonant antenna like a dipole cut for that frequency
connected to a coax and determine how to connect the coax to your radio.
If it is a portable radio try operating on the batteries as some of the
wall wart power supplies are noisy or noise on the house wiring is being
conducted to your radio through the power cord.
Now to test the antenna to see if it really helping you can disconnect
it from the radio and extend the radios whip antenna and collapse it
again reconnecting the external antenna to see which works the best.
You can put the external antenna outside away from noise generating
electrical equipment or switch them off.
Once you have a dipole making an improvement on weak signals you can
make other antenna types and antennas for other frequencies.
There are plenty of antenna sites on the web and ideas on finding local
noise sources.
--
Telamon
Ventura, California
cornytheclown
Antenna basics with formulas
http://www.electronics-tutorials.com/antennas/antenna-basics.htm
you may also want to do a search on "antenna tuners"
Bob Myers
wire
> in order to lower the resonance frequency of the wire. If I were going to
> try something similar (adding a capacitor, in series) in an attempt to
bring
> the resonance of the wire down into the 30 MHz range, what size (roughly)
> capacitor should I use? Should I just try a few with different ranges, or
> does anyone here have any suggestions?
This isn't likely to help your basic problem, which appears
to be a lack of selectivity in the radio (in other words, it
is accepting signals over too wide a bandwidth, so you hear
not only the station you're interested in, but those "to either
side" as well. Having the passband too wide also makes
for more noise in general. There are filters that can be
added (within the receiver) to improve this, but your best
bet may be to simply look for a better receiver.
Bob M.
Rich Grise
> "Dave" <db5...@hotmail.com> wrote in message
> > One manufacturer of a similar "wind-up" antenna adds a capacitor to the
Not necessary at all. With a little studying of how antennas work,
Dave could build an antenna tuner and preselector all rolled into
one, with only a few parts.
For specifics, that's a homework problem and I'm personally
currently engaged in a project much like this; I'll post when
I have something a little more concrete.
Cheers!
Rich
Dave
"Rich Grise" <nu...@example.net> wrote in message
news:UyIcc.7246$TS3....@nwrddc02.gnilink.net...
Thank you, Rich. That is just what I have decided I need. Where are you
finding your information on building such a device?
Dave
Rich Grise
> On Wed 07 Apr 2004 07:18:56a, "Dave" <db5...@hotmail.com> wrote in message
> news:c50obk$9...@library1.airnews.net:
> > "Rich Grise" <nu...@example.net> wrote in message
> > Thank you, Rich. That is just what I have decided I need. Where are
> > you finding your information on building such a device?
> I've no interest re-inventing the wheel, so if you come up with a design
> or have links to the design(s) you've settled on - and if you are
> agreeable to it - please share.
Well, I was just basically thinking of an ordinary antenna tuner,
which can be as simple as one capacitor or one inductor, or various
combinations, depending on what kind of impedance you're seeing
at the feed point.
The seat-of-the-pants way to do it is get a variable cap and
variable inductor in a range appropriate for the freq, and just
stick them in various arrangements and play with the tuning
until you get the best signal.
If you want to be scientific aboutg it, you might find something here:
http://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&q=%22antenna+tuner%22
Have Fun!
Rich
Private
I have been in a very similar situation. I used almost an identical
antenna and had fantastic results. The radio likely does not have
sufficent filtering in this case (Antenna is likely working great). I
would start by ensuring the antenna has a good ground connection to
the radio.
An antenna tuner/preselector would defantely help. Purchasing a new
or used amateur radio tuner (i.e. MFJ) 1.8Mhz-30Mhz would be the
easiest option. Adding capacitors separetely could work, but from
experience is a challenge to achive an workable solution for all
frequencies.
Homac
"Dave" <db5...@hotmail.com> wrote in message news:<c4n49g$n...@library1.airnews.net>...
Dave
operating too shabily either as it is only the "background noise" I am
trying to reduce. I hooked a 100 mH RF choke up to it with good results,
and am planning on adding another one or two similar devices in an effort to
cut down on higher frequency interference. Question: how would I ground
this antenna? I have a grounding rod right outside the window, but don't
know what to hook it too. The negative battery terminal? This radio does
have an external antenna input, but that has a plastic ring around the
outside. Open to suggestions. And thanks for the input RE purchasing a
new/used tuner.
"Private" <radio-o...@telus.net> wrote in message
news:d318809e.04040...@posting.google.com...
Dave
"Bob Myers" <nospam...@address.invalid> wrote in message
Hello Bob,
The selectivity doesn't actually seem to be too bad, as it is only the
weaker signals that I have trouble digging out of the hash and trash. It
does seem to be picking up some out-of-band signals, but they are very, very
weak. As I posted in another message, a 100 microhenry RF choke cut that
stuff out considerably, and I am planning on adding another 100 or 200
microhenry RF choke to see if that helps make the slightly stronger signals
a little more discernable. Next on the worksheet is an antenna tuner of
some sort.
Thanks all,
Yodar
around a 1" PVC pipe segment (when I was a KID I used a lacquered
toilet paper core) and take taps off it every 2-5 turns (arbitrary)
and use the selector switch to derive signal from the taps that give you
the best performance (it will vary per band) The capacitors are from
old garage sale radios and may not even be needed
This accomlishes what you have already proven with your work, that
certain frequencies can be canceled out by selection of signal
inductor-load.in series with your antenna The capacitors merely
help you tune it in more making a tank circuit that resonates with the
frequency you're "working"
I did perhaps the same thing by winding 100 turns of magnet war on a
salvaice ring torid core from a ttransistor powwer supply off a dead
computer...The antenna went to 1 end of this 100 turns and the other end
was grounded. On top this hundred turns I wound 25-40 turns and ran on
end of THAT winding to my radio's antenna IN connector and the other end
to the radio's ground
You have just made a 4:1 balun...which all in one almost does what the
couple above does...no adjustment tho
Or you can do the quick and dirty trick with a TV 300 ohm to 75 ohm
coupler, connecting the 300 ohm end to the antenna and ground as above,
and the 75 ohm connectors to your radio's antenna and ground
You wont notice the difference
Yodar
Dave wrote:
> The antenna does indeed seem to be working great, and the radio is not
> operating too shabily either as it is only the "background noise" I am
> trying to reduce. I hooked a 100 mH RF choke up to it with good results,
> and am planning on adding another one or two similar devices in an
effort to
> cut down on higher frequency interference. Question: how would I ground
> this antenna? I have a grounding rod right outside the window, but don't
> know what to hook it too. The negative battery terminal? This radio
does
> have an external antenna input, but that has a plastic ring around the
> outside. Open to suggestions. And thanks for the input RE purchasing a
> new/used tuner.
>
> dave
> db5...@hotmail.com
..
Yodar
and the diagram was cut out...how do I add it?
Yodar
Dave
take diagrams.
"Yodar" <yo...@cfl.rr.com> wrote in message
news:KXidc.438032$Po1....@twister.tampabay.rr.com...
CW
place of a roller inductor. Continuously variable and cheap.
"-=jd=-" <jd77...@HATpostmark.net> wrote in message
> The variable inductor is my stumbling block. I want that continuously
> variable functionality, but without dropping $100 - $200 for a new/used
> inductor. I'm thinking about trying to build one - but that's all I'm
> doing... just thinking...
>
> -=jd=-
> --
> My Current Disposable Email:
> jd77...@HATpostmark.net
> (Remove YOUR HAT to reply directly)
CW
"Yodar" <yo...@cfl.rr.com> wrote in message
news:KXidc.438032$Po1....@twister.tampabay.rr.com...
Frank Dresser
"-=jd=-" <jd77...@HATpostmark.net> wrote in message
>
> I'm thinking a bead (say, 1/2") threaded on a rod (brass for both bead and
> rod?), positioned so that the bead can be lifted just slightly, then slid
> along the coil - but when you release the bead, there's a bit of tension
> pressing it against the coil. I thought about the gator clip method, but
> I'm
> thinking it might be easier to fool with if I had something I could adjust
> without taking my focus off the radio.
>
> Then again, alligator clips and leads are a more widely available than the
> pseudo roller inductor parts rattling around in my head...
>
> -=jd=-
I'll suggest you try the alligator clip and wire first. It will be alot
easier to do any modifications. Also, you might find the whole experiment
isn't particularly helpful in your situation. If so, you might as well find
out right away.
Frank Dresser
CW
radios.
"-=jd=-" <jd77...@HATpostmark.net> wrote in message
news:Xns94C685775275...@63.218.45.22...
> On Fri 09 Apr 2004 12:40:57p, "CW" <clinton...@comcast.net> wrote in
> message news:MdmdneKAgZ-...@comcast.com:
>
> > For many years, it was common practice to use a lead and aligator clip
> > in place of a roller inductor. Continuously variable and cheap.
> >
>
> I'm thinking a bead (say, 1/2") threaded on a rod (brass for both bead and
> rod?), positioned so that the bead can be lifted just slightly, then slid
> along the coil - but when you release the bead, there's a bit of tension
> pressing it against the coil. I thought about the gator clip method, but
> I'm
> thinking it might be easier to fool with if I had something I could adjust
> without taking my focus off the radio.
>
> Then again, alligator clips and leads are a more widely available than the
> pseudo roller inductor parts rattling around in my head...
>
CW
"Frank Dresser" <analo...@worldnet.att.net> wrote in message
news:NTBdc.1512$K_.34795@bgtnsc05->
Rich Grise
> The antenna does indeed seem to be working great, and the radio is not
> operating too shabily either as it is only the "background noise" I am
> trying to reduce. I hooked a 100 mH RF choke up to it with good results,
> and am planning on adding another one or two similar devices in an effort
to
> cut down on higher frequency interference. Question: how would I ground
> this antenna?
Uh, you don't ground the antenna. You ground ground. :-) The ground is like
a "return" path for the current induced in the antenna by the radio wave.
> I have a grounding rod right outside the window, but don't
> know what to hook it too. The negative battery terminal?
Probably. Any handy chassis ground will be fine.
> This radio does
> have an external antenna input, but that has a plastic ring around the
> outside. Open to suggestions.
The radio might be grounded through the power cord, if it's a 3-prong.
Otherwise, just a wire from the radio's chassis to the ground rod, or
even to one of the mounting screws of a grounded outlet.
> And thanks for the input RE purchasing a
> new/used tuner.
>
> dave
As you seem to have mentioned, you have lots & lots of signal
strenth, so you actually might want to make your antenna even _less_
sensitive. What it sounds like you're looking for is selectivity,
and you do that with tuned circuits. Or you did back when I was
learning this stuff. ;-)
Hope This Helps!
Rich
Dave
Yes, a tuned circuit, I am thinking. There is currently much more signal
than I need. Is an antenna tuner what I am looking for?
I hooked up 300 microhenries worth of RF choke, which reduces the entire
signal just a hair, but that is enough to knock the noise level down
considerably. I am not yet sure, but this *may* be all I need. BTW, did
some fiddling withe the anchor of the random wire, and decided it is more
like 45 - 50 feet total. I am planning on moving it, however, and placing
it under the eaves and off to the side of the aluminum rain gutter, which
may deflate it some. Right now I have signal to waste. That may change.
Thanks for the input. Working with RF is new to me.
Rich Grise
>
> > As you seem to have mentioned, you have lots & lots of signal
> > strenth, so you actually might want to make your antenna even _less_
> > sensitive. What it sounds like you're looking for is selectivity,
> > and you do that with tuned circuits. Or you did back when I was
> > learning this stuff. ;-)
> >
> > Hope This Helps!
> > Rich
> >
> >
>
> Yes, a tuned circuit, I am thinking. There is currently much more signal
> than I need. Is an antenna tuner what I am looking for?
>
> I hooked up 300 microhenries worth of RF choke, which reduces the entire
> signal just a hair, but that is enough to knock the noise level down
> considerably. I am not yet sure, but this *may* be all I need. BTW, did
> some fiddling withe the anchor of the random wire, and decided it is more
> like 45 - 50 feet total. I am planning on moving it, however, and placing
> it under the eaves and off to the side of the aluminum rain gutter, which
> may deflate it some. Right now I have signal to waste. That may change.
>
> Thanks for the input. Working with RF is new to me.
Actually, if you've got good electrical conductivity, the aluminum
rain gutters themselves might make a passable antenna. Ground _one_
of the downspouts at the bottom end, and experiment with different
pickoff points along the length of the gutter. An antenna has
different impedances at different points along its length, based on
the wavelength of interest. And you'd add inductance and capacitance
as needed to make the whole thing resonant at the freq. you want.
(that's the philosophy of an "antenna tuner.")
It really wouldn't do any harm to look up some books on antennas
and stuff, like "The ARRL Antenna Book", and talk with practically
any radio amateur - those guys do this stuff all day long.
Cheers!
Rich
Telamon
"Dave" <db5...@hotmail.com> wrote:
Anytime you have to much signal and want to reduce it you employ an
attenuator. For coax it would be composed of three resistors in a pie
network. You would select values that would cause the input and output
resistance of the attenuator to appear 50 ohms using the source and load
impedance of the antenna and receiver so it would not generate
reflections. Additionally the resistor values would provide the voltage
division required. All calculations use ohms law. Since the radios S
meter basically is a reflection of the signal voltage a 6 dB attenuator
would cause the meter deflection to be about half what it was without
the attenuator.
If you don't care about reflections then you can make a quick and dirty
variable attenuator using a potentiometer from Radio Shack. The outer
shield of the coax goes to the same radio connection and one end of the
potentiometer, the other end of the potentiometer goes to the coax
center conductor and the potentiometer wiper goes to the radio input
where the coax center conductor would normally go. A 10K potentiometer
would be good to use.
--
Telamon
Ventura, California
Dave
I thought about trying to use the rain gutter as an antenna, but decided
against it for a number of reasons. The main reason was that I didn't want
to fiddle with trying to get good electrical connections between the many
pieces. Anything I did to it would have to be most asthetically appealing,
or I would never hear the end of it from my wife. She absolutely hates
having a piece of wife laying across the roof, and can't wait until I fix it
in place underneath the eaves.
I have a copy of the latest edition of Joe Carr's Practical Antenna Handbook
(I think that's what it's called) but don't have a tremendous amount of time
to spend with it. So much else to do... I need to set aside a couple hours
every night and just plow through it.
Thanks again for your input.
Dave
"Telamon" <telamon_s...@pacbell.net.is.invalid> wrote in message
news:telamon_spamshield-C...@news.sf.sbcglobal.net...
Thanks for the info. Not really sure which avenue I am going to persue at
this point. Trying to sort out all the options. I appreciate the input.
Dave
"-=jd=-" <jd77...@HATpostmark.net> wrote in message
> On Sun 11 Apr 2004 01:39:04a, "Dave" <db5...@hotmail.com> wrote in message
> news:c5amel$q...@library2.airnews.net:
>
> > She absolutely hates
> > having a piece of wife laying across the roof, and can't wait until I
> > fix it in place underneath the eaves.
> >
>
>
>
>
> -=jd=-
> --
LOL! I meant to say "a piece of WIRE..." Guess I was thinking something
else.
RHF
So you have a Sangean ATS -505 and your 'problems' are Antenna
Overload and Noise Levels.
* Consider a 'smaller' shorter Antenna will reduce the overload problems.
* Consider a Low Noise Antenna Design will reduce the noise problems.
{LOW NOISE SWL ANTENNA - popularized by John Doty}
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/2
http://www.anarc.org/naswa/badx/antennas/low-noise_antenna.html
For a simple 'external' Shortwave Antenna to use with the Sangean
ATS-505 'portable' Shortwave Radio, using the 1/8" Mono-Jack
External Shortwave Antenna Input. Consider a Random Wire
Antenna using a Matching Transformer and Ground for Low Noise
and Wide Range Frequency Coverage.
PARTS: Here is a simple SWL Antenna Idea using a few common
RadioShack TV Antenna type parts:
Catalog #: 15-1174 = 25~50 Foot 300 Ohm (Flat) TV Twin-Lead
Catalog #: 15-1230 = 75 to 300 Ohm Matching Transformer (2 Ea.)
Catalog #: 274-286 = 1/8" Mono (Phone) Plug
Catalog #: Catalog #: 15-1579 = 25~50 Foot Coax Cable with F Connectors
NOTE: This is an 'improved' Random Wire SWL Antenna using "TV"
Parts for 'reducing' Man Made Noise (RFI EMF) that is generated in
or near most modern homes/buildings.
EXTERNAL "OUTSIDE" SWL ANTENNA:
The Antenna [Loop] Element is Stretched outside Horizontally or
in the shape of an Inverted "L". The Antenna [Loop] Element is
formed by connecting the two ends of the Far-End of the 300 Ohm
TV Twin Lead. This forms a continuous single skinny horizontal
flat loop going out and back. This also represents a Balance
300 Ohm Load to match-up with the 300 Ohm Matching Transformer.
The 300 Ohm Leads of the Matching Transformer connects to the
Near-Ends of the Loop Antenna Element. The 75 Ohm F Connector
of the Matching Transformer is connected to the 75 Ohm Coax Cable.
The 75 Ohm Coax Cable acts as the Lead-In from the Outside to
inside the house to the radio shack. The other end of the 75
Ohm Coax Cable is connected to the 75 Ohm F Connector of the
Matching Transformer. The Radio-End of the Coax Cable F Connector
would connect to a 75 to 300 Ohm Matching Transformer; and then
into a 1/8" Mono-Plug to plug into the Radio.
NOTE: Using the 300 Ohm TV Twin Lead in a Skinny Flat Loop
Antenna should balance-cancel-reduce most man made noise and be
Omni-Directional.
GROUND: Find a Grounding Point within/about your dwelling.
Secure a good Grounding Point for your Radio and Antenna.
Run a Heavy & Short Ground Wire to your Radio. Locate the
Ground Terminal on your Radio. Attach/Secure the Ground Wire
to the Coax Cable and/or the Radio's Ground Terminal.
FWIW: This Antenna using common TV Antenna type parts should
be effective as SWL Antennas above 5MHz and beyond 30MHz.
iane ~ RHF
.
Some Say: On A Clear Day You Can See Forever.
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/502
I BELIEVE: On A Clear Night...
You Can Hear Forever and Beyond - The Beyond !
.
.
= = = "Dave" <db5...@hotmail.com> wrote in message
= = = news:<c4n49g$n...@library1.airnews.net>...
> I recently hooked up a thirty-six foot (plus or minus a couple of feet)
> piece of four-stranded wire with alligator clip to the internal "whip"
> antenna of my portable shortwave receiver, for the extra performance such a
> device offered. It works so well that I now cannot usually use my "DX"
> setting because of all the background noise (sounds like hundreds of other
> broadcasts vying for attention.) I don't know the frequency source of all
> this background noise, but would like to filter out as much of it as I can.
> One manufacturer of a similar "wind-up" antenna adds a capacitor to the wire
> in order to lower the resonance frequency of the wire. If I were going to
> try something similar (adding a capacitor, in series) in an attempt to bring
> the resonance of the wire down into the 30 MHz range, what size (roughly)
> capacitor should I use? Should I just try a few with different ranges, or
> does anyone here have any suggestions?
>
> TIA
>
> Cross-posted between sci.electronics.basics and rec.radio.shortwave
>
>
> Dave
> db5...@hotmail.com
>
.
Dave
really don't *think* I am overloading the set. Only problem I have is
digging the weak (but desired) signals our of the background noise
surrounding them. In another post I mentioned Voice of Korea's Central and
South American broadcast as the point of interest. It is just at the same
level as the background noise that doesn't interfere with other broadcasts
like the BBC on 5975 kHz or Radio Havana, Cuba on 9820 kHz (or Radio China
International, originally from Taiwan and rebroadcast through some place in
Florida, which frequency I can't remember at the moment.) It is only the
weak signals I am having trouble with. If I tune into WWV our of Ft.
Collins CO I can barely make out some out-of-band signals coming in, but
they are so weak as to be vanishing. Does this still sound like
overloading? Because the troublesom signals are also very weak, I am
thinking that a preselector will probably take care of my problems. (I am
still tempted to abandon my random wire and install your suggested antenna
just because it sounds so much more sophisticated. Will let you know.)
Thanks for the feedback.
"RHF" <rhf-say...@pacbell.net> wrote in message
news:ee137ed4.04041...@posting.google.com...
Dave
question: The twin-lead is 300 ohm, connected to a 300/75 ohm matching
transformer, connected to 75 ohm coax. Then the coax is connectect to
another 75/300 ohm matching transformer, which is connected to the 1/8" mono
plug to plug into the external antenna jack? Is the 1/8" jack a 300 ohm
impedance connection? Somehow I thought it would be 50 or 75 ohms, like
coax. Do I need some 300 ohm coax to put between the second transformer and
the plug?
Thanks,
"RHF" <rhf-say...@pacbell.net> wrote in message
news:ee137ed4.04041...@posting.google.com...
RHF
At the Radio-End of the 75 Ohm Coax Cable "F" Connector you can
use a standard 75-300 Ohm Matching Transformer and then connect
it to a Mini-TV External Antenna Adapter. [ RadioShack {Canada}
Catalog #: 15-1148 = 75 to 300 Ohm Mini-Plug Adapter ]
MINI-PLUG-ADAPTER=> http://tinyurl.com/23nsh
FWIW: Some RadioShacks and other electronics stores have an "Adapter"
that directly connects an "F" Connector to a /18" Mono-Phone-Jack.
Please Note: That a 'connection' to a good earthen Ground is
needed to one of the "F" Connectors of the 75 Ohm Coax Cable.
You can use a #14 Wire with a RadioShack Catalog #: 278-002
Heavy-Duty Claw Insulated Test/Jumper Cable Sets. Or, simply
use several windings of bare wire wrapped around one of the "F"
Connectors with a small metal hose clamp to secure the wire.
iane ~ RHF
.
.
= = = "Dave" <db5...@hotmail.com> wrote in message
= = = news:<c5l1ot$g...@library1.airnews.net>...
Dave
Dave
Thanks for the info. I picked up a 300/75 ohm mini-plug adapter at the
store, but failed to get the second 75/300 ohm matching transformer to go
between it and the coax. Tomorrow.
Question: I have an odd situation, and can either install a 1/4 wave dipole
or a half-wave "random" wire loop (I think). Right now the grounding rod is
immediately below where the dipole would go, and I think I could drop the
300 ohm twin-lead down to it where I would ground one side (I think I have
this right, please correct me if I am wrong). At that same point I would
ground the shield of the coax, and hook the other side of the dipole to the
coax center conductor. Coax would travel 10 feet or so to my window and the
radio. Other option involves moving the grounding rod and doing something
similar with the twin-lead as a long loop, grounding one side of that and
coax from the other side of the window. Assuming these are workable ideas,
which do you think would work best? Again, [please don't hesitate to tell
me if I am full of crap. RF is new to me.
I really do appreciate your help. Like I said before, RF is totally new to
me.
Thanks,
RHF
>
> Thanks for the info. I picked up a 300/75 ohm mini-plug adapter at the
> store, but failed to get the second 75/300 ohm matching transformer to go
> between it and the coax. Tomorrow.
>
> Question: I have an odd situation, and can either install a 1/4 wave dipole
> or a half-wave "random" wire loop (I think).
A "Random" Wire Antenna is simply that = Any Length that FITS
the Space that is Available to put up and Antenna.
For these general types of Low Noise Antennas. The Inverted "L"
{Shaped} Antenna lends itself to the design the best.
Run the Horizontal Arm for as long as you can at your roof line.
Run the Vertial Leg down to your Ground Rod Location.
Make your 'primary' Grounding Point "Connection".
Run your Coax Cable from the Grounding Point to your Radio.
.
.
> Right now the grounding rod is immediately below where the
> dipole would go, and I think I could drop the 300 ohm twin-lead
> down to it where I would ground one side (I think I have
> this right, please correct me if I am wrong).
Initially do NOT Ground the 300 Ohm Twin Lead.
[ This is the Antenna Side of the Matching Transformer. ]
The Near-End of the 300 Ohm Twin Lead is connected across the
300 Ohm-Side of the Matching Transformer; and the other Far-End
of the 300 Ohm Twin Lead Wires are Connected (Joined) Together.
This forms a Long Shinny Loop Antenna Element.
FWIW: This is a very 'quiet' Antenna (almost sounds dead)
until you get spot on the frequency and then the signal is there.
.
.
> At that same point I would ground the shield of the coax,
> and hook the other side of the dipole to the coax center conductor.
> Coax would travel 10 feet or so to my window and the radio.
First simply try Grounding the Outer-Shield of the Coax Cable ONLY.
.
.
> Other option involves moving the grounding rod
IF - You move the Ground Rod. Place it so you can have an
Inverted "L" Antenna with the longest Horizontal Arm 'possible'.
(30 <60-90> 120 Feet)
iane ~ RHF
.
.
Dave
with on this subject at this point, and since I did join the Yahoo!
Shortwave Antenna group, I am going to try (that is, do my best) to move
this over to that group. All posts from this point on, at least on this
particular thread, will be made there. This text will be posted there in a
few minutes, alongwith a couple more questions and clarifications.
Thanks for introducing me to that group, which I am trying to get more
into, and thanks for your help so far.
"RHF" <rhf-say...@pacbell.net> wrote in message
news:ee137ed4.04041...@posting.google.com...
CW
an option.
"Dave" <db5...@hotmail.com> wrote in message
news:c5ptm1$5...@library2.airnews.net...
Dave
OKAY, here are the new questions and clarifications...
Thanks for clearing up for me why it is called a random wire. I
thought that was just what they called it when it wasn't 1/4 or 1/2
wavelength.
I realized something today- I think I am actually talking about
installing a HALF-WAVE dipole, not a 1/4 wave. Since it is twin-lead
I am talking about, and since it is going to be joined at the far
end, each leg would be twice the 1/4 wavelength of the physical
cable. Am I right here?
Correct me if I am wrong, but you do ground one side of a dipole,
right? So one leg would be grounded along with the shield of the
coax, right?
What I am visualizing is two pieces of twin-lead, one called A (left)
and the other called B (right.) A would have one side of one end
soldered to the ground rod (call this the "near" end) with the other
side of that end hanging out in space. The rest of that piece of
twin-lead (side A) would go up the side of my house to the eaves and
over several meters. The far end of A would have the two conductors
soldered together. B would have one side of the "near" end attached
to the appropriate lead of a 300/75 ohm matching transformer, which
has it's other lead soldered to the grounding rod and goes to 75 ohm
coax. The other side of the "near" end of B hangs out in space. B
would then go up the side of the house to the eaves, just like A, but
would then stretch several meters in the other direction. The "far"
end of B would also have the two conductors soldered together. Each
leg is a little over 15 meters long (counting the part that goes up
as well as the part that goes over), which would make the whole
dipole a half-wavelength for some frequency slightly below 10 MHz.
(Have I got this right?)
The coax would travel approx. 4 meters to my window, where it would
go through another matching transformer and into the external antenna
input of the radio.
Wouldn't that be a half-wave dipole?
Would it matter that the side of the house is covered in steel
siding, against which it would be lying?
Would this work, or would an inverted L still be better (or
quieter)? I could put the grounding rod immediately outside my
window, which might enable me to make the long leg of the L somewhat
longer than the combined 30 meters of the dipole. That would make
for a shorter run of coax, but the soil would be drier thereby making
for a poorer ground (where it is now, the grounding rod sits next to
the output of a downspout.)
If I went with the inverted L (with joined conducters on the far end
to make a loop) would I still ground one side of the twin-lead? Do
you ground one side of a loop?
Okay, I've written War and Peace. Sorry for the great number of
questions, I'm just trying to understand the fundamentals of
installing an antenna. I hope I am not trying your patience.
Thanks,
Dave
I also posted another message asking if anyone had read the book called
Shortwave Listener's Antenna Handbook published by TAB books in '82. I saw
it on Amazon.com, but they didn't have any ratings for it. If anyone HERE
has read it, please share your opinion with me.
"CW" <clinton...@comcast.net> wrote in message
news:9uCdnXCGx68...@comcast.com...