Antenna impedance
-=jd=-
of the woodlines on my property. It really overloaded the receiver, but
with an external attenuator, it was a very useable signal snagger.
Last week, the new wore off and I decided to change it. I now have about
100' of that wire arranged in horizontal triangular loop.
The happy surprise is that the S/N ratio is much, much better.
The one thing that I would like to do is try to figure out the actual
characteristic impedance of the antenna. I've found information that shows
me how to do this with a noise-bridge, but I don't have one of those.
I was wondering if anyone knows of a link or a formula for finding a
relatively close "ballpark" figure for characteristic impedance. I'm
thinking there isn't (without the inclusion of one or more physical
measurements) due to all of the variables involved.
To add to the dificulty, the antenna is over sloping terrain and I recall
that height above terrain affects impedance.
The end goal is to match a coax feed to the antenna as closely as
*reasonably* possible. I understand that there's the distinct possibility
that after going through all the effort to determine what ratio is needed
for the transformer, a SWAG may well have produced the same or similar
results... But, it's a hobby and I have the time.
-=jd=-
--
My Current Disposable Email:
jd77...@HATpostmark.net
(Remove YOUR HAT to reply directly)
N8KDV
-=jd=- wrote:
A general rule of thumb might say that for that single random wire you'd be
looking at 500 ohms, give or take.
Here's some good reading material:
http://members.aol.com/DXerCapeCod/z_transformers.pdf
http://www.dxing.info/equipment/impedance_matching_bryant.pdf
Steve
Holland, MI
Drake R7, R8 and R8B
-=jd=-
message news:409E5940...@nospam.iserv.net:
Thanks again. That first pdf triggered another search I hadn't thought of
that winnowed down the results a bit. From what I can gather, I'm faced
with the 3 most common impedences mentioned (from various links): -
"...typically 102ohms..." - "...varying from 300 to 600ohms, depending on
height..." - "...up to 1000 ohms..."
I think the only way to know for sure is via a noise-bridge or just say to
heck with it, split the difference and go with your 500ohm figure.
Then again, I guess I could try all three. It would be my distinct luck to
try all three and not be able to discern that much of a difference with my
uncalibrated ears. I really need to get a noise-bridge (if I'm going to
keep trying different things), if only to satisfy my curiosity.
-=jd=-
message news:409E5940...@nospam.iserv.net:
>
>
Thanks again. That first pdf triggered another search I hadn't thought of
that winnowed down the results a bit. From what I can gather, I'm faced
with the 3 most common impedences mentioned (from various links): -
"...typically 102ohms..." - "...varying from 300 to 600ohms, depending on
height..." - "...up to 1000 ohms..."
I think the only way to know for sure is via a noise-bridge or just say to
heck with it, split the difference and go with your 500ohm figure.
Then again, I guess I could try all three. It would be my distinct luck to
try all three and not be able to discern that much of a difference with my
uncalibrated ears. I really need to get a noise-bridge (if I'm going to
keep trying different things), if only to satisfy my curiosity.
-=jd=-
-=jd=-
in message news:Xns94E487101F51E...@63.218.45.21:
> On Sun 09 May 2004 12:16:00p, N8KDV <n8...@nospam.iserv.net> wrote in
> message news:409E5940...@nospam.iserv.net:
>
>>
>>
>>
>> A general rule of thumb might say that for that single random wire
>> you'd be looking at 500 ohms, give or take.
>>
>> Here's some good reading material:
>>
>> http://members.aol.com/DXerCapeCod/z_transformers.pdf
>>
>> http://www.dxing.info/equipment/impedance_matching_bryant.pdf
>>
>> Steve
>> Holland, MI
>> Drake R7, R8 and R8B
>>
>> http://www.iserv.net/~n8kdv/dxpage.htm
>>
>
>
>
> Thanks again. That first pdf triggered another search I hadn't thought
> of that winnowed down the results a bit. From what I can gather, I'm
> faced with the 3 most common impedences mentioned (from various links):
> - "...typically 102ohms..." - "...varying from 300 to 600ohms, depending
> on height..." - "...up to 1000 ohms..."
>
> I think the only way to know for sure is via a noise-bridge or just say
> to heck with it, split the difference and go with your 500ohm figure.
>
> Then again, I guess I could try all three. It would be my distinct luck
> to try all three and not be able to discern that much of a difference
> with my uncalibrated ears. I really need to get a noise-bridge (if I'm
> going to keep trying different things), if only to satisfy my curiosity.
>
> -=jd=-
Huh? Is there an echo in here?
Sorry bout' that - I'm not sure how I managed that double-post...
CW
mismatch returns.
"-=jd=-" <jd77...@HATpostmark.net> wrote in message
news:Xns94E47B4284EBC...@63.218.45.21...
N8KDV
CW wrote:
> Even if you do match it, it will be at only one frequency. At any other, the
> mismatch returns.
There are ways to get more of a broadband match, via the use of a matching
transformer.
Drifter
and bring it to the radio by coax; how would
this be grounded for static and lighting?
i would rather ground outside and not at the
radio...thanks...
Drifter...
N8KDV
Drifter wrote:
You can do it several different ways. Here, I use the type of
transformer that utilises a ground at the feed point. Hence, the antenna
itself is always at DC ground.
It's simply a matter of how one connects the windings. It's certainly
possible to short the one end of the winding to the coax connector, and
then just get away with a ground at the receiver.
I believe this is the method that the RF Systems MLB balun uses. Myself,
I prefer to have a ground at the feed point.
From the feed point here it's about 9' down to an 8' or so ground rod.
I also have a separate ground for the receiver(s), and I would still
recommend it's use.
I used to offer them for sale, and could build one any way the customer
wanted. It's time consuming to make them though so I jut drifted away
from it. Last time I wound one up was for a fellow in Ireland a couple
years ago, and he has good success with it. I think I sold about 275 of
them, but I just could not keep up.
If you have other questions I'll try and help you out. I'm much better
at explaining in person and if I have some exhibits to use!
CW
"Drifter" <dri...@pgh.com> wrote in message
news:409E7DAE...@pgh.com...
Drifter
looked at the 20m site. 9-1 seems to be the way to go.
i 'll try making one of these. don't have the junk box
i had as a youngster, (had my ticket in the 50's). used
my Dad's radios, never had my own set-up and never seemed
to get the time to get back into it. after my wife died, i
moved farther into the country. quiet out here. and, i got
about an acre here, should be lots of room to run wire.
i had looked at an alpha-delta. thought i'd try to brew
my own. been using a an-lp1 here. want to get outside now.
picked up 2 RS long wires and stranded 18 for a song and
a danced at a local winter fest. Breezshooters fest next
month, should find the rest of parts and a mini box. will
give it a go. i feel 55 is still young enough to fall off
a roof. you recommend long wire or something like an
inverted V? thanks a lot Steve...
Drifer...
N8KDV
Drifter wrote:
I've found that around 70' or so works pretty well for all 'round use.
Start going longer and the antenna starts to get more directional with
respect to the direction the wire is running.
Gotta go! The boomers are moving in again!
Volker Tonn
Drifter schrieb:
Be aware that grounding does not save your radio from a lightning shock
hitting your antenna. It will for some chance only prevent to burn down
your house. ALL electronical stuff in your house may be dead then.
CW
"Volker Tonn" <screw...@mailberlin.net> wrote in message
news:newscache$skygxh$vek$1...@news.berlinweb.de...
Drifter
Drifter...
Volker Tonn
CW schrieb:
But for sure you can not do it by yourself and it will cost a LOT. And
at least there is NO insurance it will work under ALL circumstances.
Best (additional) way to go is to disconnect the antenna when leaving
the shack or lightning is coming up whilst you are in your shack.
PS: Quoting corrected.
RHF
Read these three Links 'presented' by John Doty:
[ Hosted by The Association of North American Radio Clubs "ANARC".]
Longwire Impedance Matching. {Check-Out the Graphs}
http://www.anarc.org/naswa/badx/antennas/SWL_longwire.html
Actually, a fixed Matching Transformer can dramatically reduce the
wild swings in Antenna Efficiency that a Coax Fed Wire Antenna exhibits.
Grounding is the KEY to Good Reception
http://www.anarc.org/naswa/badx/antennas/grounding.html
Low Noise Antenna Connection
http://www.anarc.org/naswa/badx/antennas/low-noise_antenna.html
iane ~ RHF
.
.
= = = Drifter <dri...@pgh.com> wrote in message
= = = news:<409E7DAE...@pgh.com>...
.
Drifter
thanks...
Drifter...
Frank Dresser
"-=jd=-" <jd77...@HATpostmark.net> wrote in message
news:Xns94E47B4284EBC...@63.218.45.21...
>
> The one thing that I would like to do is try to figure out the actual
> characteristic impedance of the antenna. I've found information that shows
> me how to do this with a noise-bridge, but I don't have one of those.
>
> I was wondering if anyone knows of a link or a formula for finding a
> relatively close "ballpark" figure for characteristic impedance. I'm
> thinking there isn't (without the inclusion of one or more physical
> measurements) due to all of the variables involved.
>
[snip]
Reg Edwards has an interesting webpage:
http://www.btinternet.com/~g4fgq.regp/
He has many rather complicated formulas written into easy to use programs.
One of the RJELOOP programs might be helpful:
http://www.btinternet.com/~g4fgq.regp/page3.html#S301"
Be aware that the impedance will vary considerably with frequency, and will
have a large reactive component at most frequencies.
Aside from a noise bridge, MFJ sells some antenna analyzers, if you want to
spend the money:
http://www.mfjenterprises.com/products.php?catid=49
The ARRL Antenna book is a good reference. The Radio Amateur's Handbook has
less antenna info than their Antenna Book, but it may be available in your
public library.
LB Cebik has a tremendous amount of antenna info on his website. Loops(and
most everything else) are there:
http://www.cebik.com/gup/groundup.html
http://www.cebik.com/radio.html
A grid dip meter is a cheap antenna toy. It is a metered oscillator which
can determine the resonant points of circuits. I got mine for about $15.
If you get one, be sure you get the coils!
I last used my grid dip meter to cut a perfectly resonant twin lead folded
dipole at 162 MHz. The perfectly resonant folded dipole worked about as
well as a meter test lead clipped to the antenna terminal. That's the way
it often goes with receiving antennas. The radios aren't usually very fussy
.
Sometimes the best approach for receiving antennas is to just string some
wire, play with transformers and experiment.
Frank Dresser
-=jd=-
message news:409E81ED...@nospam.iserv.net:
>
>
> Drifter wrote:
>
>> Steve, if i were to mount something like that,
>> and bring it to the radio by coax; how would
>> this be grounded for static and lighting?
>> i would rather ground outside and not at the
>> radio...thanks...
>
> You can do it several different ways. Here, I use the type of
> transformer that utilises a ground at the feed point. Hence, the antenna
> itself is always at DC ground.
That's the method I used with the end-fed random. I had built a static
bleeder to go with it, which was just silly. I experienced a mental vapor-
lock and didn't recognize that the xformer provided a direct DC path to
ground on it's own. It could have been that I just wanted to build
something - idle hands and all...
>
> It's simply a matter of how one connects the windings. It's certainly
> possible to short the one end of the winding to the coax connector, and
> then just get away with a ground at the receiver.
>
> I believe this is the method that the RF Systems MLB balun uses. Myself,
> I prefer to have a ground at the feed point.
>
> From the feed point here it's about 9' down to an 8' or so ground rod.
>
> I also have a separate ground for the receiver(s), and I would still
> recommend it's use.
I have the coax passing through a grounding block on an 8' ground rod
prior to the receiver.
Now, with the loop, I'm using the same transformer from the end-fed
random, except now each side of the primary is connected to the loop; each
side of the secondary connects to the coax shield and center conductor.
So, there is no direct DC path to ground from the loop antenna element,
but there is also no direct DC path from the antenna element to the coax.
If/When static builds on the antenna wire, I have no idea where it goes
(Munchkin land?).
Is it within the realm of realistic possibilities that if the static
builds to a sufficient level, it could potentially arc within the xformer
housing from the primary to the coax (about 2")? I'm not talking about a
near or direct lightning hit, just regular old static buildup.
I'm also thinking that without a noise-bridge, my best bet is a trial and
error comparison. Joe Carr sez that at less than 1 wavelength, large loops
can reach a feedpoint impedance of up to 3000 ohms (I had to read it twice
to make sure); but at a full wavelength or longer, it pretty much stays at
around 100 ohms. Various sources show anywhere from no match needed, all
the way up to a 30:1 match is needed. I think there's just too many
variables to know for sure. So, trial and error it is. I'm going to try a
30:1, a 10:1 and a 1:1 toroid xformer to see what differences, if any, I
can detect just with the naked "earball". In the absence of any
discernable difference, I'm going to at least use the 1:1, if only to
maintain the DC seperation between the antenna element and the coax.
I think I'm on a sane track, given my situation - or do ya'll think I'm on
crack?
Dale Parfitt
>
> I'm also thinking that without a noise-bridge, my best bet is a trial and
> error comparison. Joe Carr sez that at less than 1 wavelength, large loops
> can reach a feedpoint impedance of up to 3000 ohms (I had to read it twice
> to make sure); but at a full wavelength or longer, it pretty much stays at
> around 100 ohms. Various sources show anywhere from no match needed, all
> the way up to a 30:1 match is needed. I think there's just too many
> variables to know for sure. So, trial and error it is. I'm going to try a
> 30:1, a 10:1 and a 1:1 toroid xformer to see what differences, if any, I
> can detect just with the naked "earball". In the absence of any
> discernable difference, I'm going to at least use the 1:1, if only to
> maintain the DC seperation between the antenna element and the coax.
>
find the classic 9:1 toroidal transformer only functions as a 9:1 over a
relatively narrow frequency range- whereas a binocular core will behave as a
9:1 over almost 2 decades. Somewhere here I have a network analyzer plot
comparing a toroidal vs binocular transformer.
--
Dale W4OP
for PAR Electronics, Inc.
John Doty
>>In addition to the end Z varying radically with frequency, you will also
>
> find the classic 9:1 toroidal transformer only functions as a 9:1 over a
> relatively narrow frequency range- whereas a binocular core will behave as a
> 9:1 over almost 2 decades. Somewhere here I have a network analyzer plot
> comparing a toroidal vs binocular transformer.
It depends a lot on the size of the transformer. You can get two decades
from a tiny one made with a TV balun toroid. One trick is to keep the
total length of wire in the transformer below about 5% of a wavelength
at the highest frequency of interest.
The antenna's Z does indeed vary a great deal, from 10's to 1000's of
ohms. If you plot it in the complex plane, it makes a spiral centered at
the antenna's *characteristic* Z, which for an inverted L is generally
in the range of 300-700 ohms. Matching to an impedance near the center
of the spiral yields a system that is not perfectly matched at any
frequency, but is adequately matched over a wide range of frequencies.
-jpd
YODAR
Yeah !
But the blinking NE-2 during a thunderstorm is kinda entertaining!
(I had the same brain fart) ;>)
it seemed like the simple loading of the antenna thru the "Balun"
caused noise to drop by 50% and my station count at least doubled
(but I still cant get New Zealand---I need my sleeeep!)
I tested the concept first with a 300/75 tv-cable balun
Yodar
Eric F. Richards
> But for sure you can not do it by yourself and it will cost a LOT. And
> at least there is NO insurance it will work under ALL circumstances.
> Best (additional) way to go is to disconnect the antenna when leaving
> the shack or lightning is coming up whilst you are in your shack.
>
Not true. You have to be anal-retentive as hell to make sure that it
is done right, but you can do it properly using the right equipment.
Polyphaser or I.C.E. protectors do the job well, but they must be
mounted on an appropriate ground window. The object of the game is
not to have your equipment at ground potential; rather the object is
to have the potential on all the equipment rise and fall together so
there is no differential amongst the equipment.
There is quite a bit of introductory material at www.polyphaser.com.
Eric
--
Eric F. Richards, efr...@dim.com
"Nature abhors a vacuum tube." -- J. R. Pierce, Bell Labs, c. 1940
John Barnard
summer at my QTH, late day thunderstorms are common and on one such day I
did have the antenna disconnected from my Drake R-8B but a FET still managed
to get fried and I needed to send the radio back to Drake for repair.
Regards
John Barnard
RHF
Three things "To Do" during Thunder and Lightening Events:
1. Dis-Connect 'all' Antennas and Ground them to the Ground Bus
in your Shack.
2. Use Shorting Plugs and Wires on 'all' your Radio/Receivers
Antenna Inputs.
3. Have a small 'all' Metal Foot Locker or Cabinet to place
your Radios/Recivers in for Safety.
iane ~ RHF
.
.
= = = John Barnard <jf...@shaw.ca> wrote in message
= = = news:<40A6213B...@shaw.ca>...
.
Telamon
wrote:
> Is there much one can do for sensitive electronics? For example, during the
> summer at my QTH, late day thunderstorms are common and on one such day I
> did have the antenna disconnected from my Drake R-8B but a FET still managed
> to get fried and I needed to send the radio back to Drake for repair.
I You do not know what happened. The radio might have been damaged
before you disconnected it. Sometimes the damaged FET does not fail
right away. There might have been a static charge on the antenna that
blew the FET when you went to reconnect it.
I consider myself very fortunate that I do not live in a lightening zone
and so do not have these problems but I do not use the type of antennas
most susceptible to this kind of damage.
Loop antennas are the safest to use as long as you make ground contact
first with the radio upon reconnection. If you use a Marconi type of
antenna, be sure to use a coupling transformer that is grounded in some
way to give the static charge a place to go.
The damaging pulse from lightening needs some kind of clamping device.
Those can be bought at the same outfits that sell antennas.
--
Telamon
Ventura, California
Eric F. Richards
> Is there much one can do for sensitive electronics? For example, during the
> summer at my QTH, late day thunderstorms are common and on one such day I
> did have the antenna disconnected from my Drake R-8B but a FET still managed
> to get fried and I needed to send the radio back to Drake for repair.
>
First off, it could have been damaged by a surge and failed later.
Second off, with reputable lightning supressors such as Polyphasers,
properly set up, the radio is actually safer than it is when
disconnected because the supressor will crowbar (dead-short)
nanoseconds after the strike starts, when the threshold voltage is
reached. It remains shorted as long as current is flowing.
It should be noted that a simple static discharge such as touching a
doorknob and getting a spark has to be about 3000 volts before a
visible spark occurs. That is way above the crowbar voltage of the
Polyphasers.
> Regards
>
> John Barnard
>
> "Eric F. Richards" wrote:
>
> > Volker Tonn <screw...@mailberlin.net> wrote:
> > > But for sure you can not do it by yourself and it will cost a LOT. And
> > > at least there is NO insurance it will work under ALL circumstances.
> > > Best (additional) way to go is to disconnect the antenna when leaving
> > > the shack or lightning is coming up whilst you are in your shack.
> > >
> >
> > Not true. You have to be anal-retentive as hell to make sure that it
> > is done right, but you can do it properly using the right equipment.
> > Polyphaser or I.C.E. protectors do the job well, but they must be
> > mounted on an appropriate ground window. The object of the game is
> > not to have your equipment at ground potential; rather the object is
> > to have the potential on all the equipment rise and fall together so
> > there is no differential amongst the equipment.
> >
> > There is quite a bit of introductory material at www.polyphaser.com.
> >
> > Eric
> >
> > --
> > Eric F. Richards, efr...@dim.com
> > "Nature abhors a vacuum tube." -- J. R. Pierce, Bell Labs, c. 1940
--
Eric F. Richards
efr...@dim.com
"The weird part is that I can feel productive even when I'm doomed."
- Dilbert