Antennas - magic science or black art?

7/23/2006 12:48:05 AMPeter Balazsy

I know that there are plenty of seemingly unexplainable antenna tricks. I've seen ads for AM antenna signal boosters that you place near your radio and supposedly get improved performance of mucho buck$.

Well I just had a very nice and unusual (to me) antenna learning experience a few mineuts ago on my work bench.

I have a Bendix 526a upside down playing there nicely after I just recapped it. It has a loop antenna which happens to be facing toward the front of my bench.

I was about to start work on a Zenith 6d-614 which also has a type of square-box-shapped loop antenna too.

As I pulled the Zenith out of it's case I set it down near the Bendix 525 such that the two antennas just happened to be about 2 inches away from each other.

Now the Zenith is without power, yet as the two units came close... the Bendix suddenly went up almost double in signal and output!

As I positioned the Zenith further and nearer I found that the the optimum distance is just about 2 inches. I tried rotating it in various angles as well yet 2 inches and straight aligned was the optimum.

... but the real interesting thing was... that I found that the Bendix signal got even stronger as I "tuned" the Zenith dial (no power) to the SAME station as the Bendix.
It was so funny tuning the un-powered Zenith and listening to the Bendix volume go up and down!

Just having an RF-only-powered antenna-tank-circuit in close proximity coupled it's signal right over from it to the other antenna.

I don't know what I learned here yet lol.
... perhaps that double antennas work better than one?? lol
I don't know. All I know is I just discovered it and I'm repoting back to headquarters here...

7/23/2006 1:38:52 AMNorm Leal

Hi Peter

Having a second turned circuit nearby can bring up the signal and narrow the bandwidth. The same idea can be used in a radio using more than one tuned circuit. Try tuning your Zenith to another frequency. Signal strength on your Bendix will go down.

You will find crystal sets made this way. Two or 3 tuned circuits will sharpen tuning.

Norm

:I know that there are plenty of seemingly unexplainable antenna tricks. I've seen ads for AM antenna signal boosters that you place near your radio and supposedly get improved performance of mucho buck$.
:
:Well I just had a very nice and unusual (to me) antenna learning experience a few mineuts ago on my work bench.
:
:I have a Bendix 526a upside down playing there nicely after I just recapped it. It has a loop antenna which happens to be facing toward the front of my bench.
:
:I was about to start work on a Zenith 6d-614 which also has a type of square-box-shapped loop antenna too.
:
:As I pulled the Zenith out of it's case I set it down near the Bendix 525 such that the two antennas just happened to be about 2 inches away from each other.
:
:Now the Zenith is without power, yet as the two units came close... the Bendix suddenly went up almost double in signal and output!
:
:As I positioned the Zenith further and nearer I found that the the optimum distance is just about 2 inches. I tried rotating it in various angles as well yet 2 inches and straight aligned was the optimum.
:
:... but the real interesting thing was... that I found that the Bendix signal got even stronger as I "tuned" the Zenith dial (no power) to the SAME station as the Bendix.
:It was so funny tuning the un-powered Zenith and listening to the Bendix volume go up and down!
:
:Just having an RF-only-powered antenna-tank-circuit in close proximity coupled it's signal right over from it to the other antenna.
:
:I don't know what I learned here yet lol.
:... perhaps that double antennas work better than one?? lol
:I don't know. All I know is I just discovered it and I'm repoting back to headquarters here...

7/23/2006 1:43:52 PMMarv Nuce

Peter,
This would be equivalent to adding more tuned circuit elements or more physical elements to a large outdoor antenna. The unpowered radio loop is broadly tuned to the AM band, but actually tuning it brings the loop and its antenna coil into resonance at the other radio frequency, and enhancing its loop antenna performance. There is no added gain per se, but this simply sharpens/narrows the bandwidth of the antenna circuit of the powered radio, giving an apparent gain.

marv

:I know that there are plenty of seemingly unexplainable antenna tricks. I've seen ads for AM antenna signal boosters that you place near your radio and supposedly get improved performance of mucho buck$.
:
:Well I just had a very nice and unusual (to me) antenna learning experience a few mineuts ago on my work bench.
:
:I have a Bendix 526a upside down playing there nicely after I just recapped it. It has a loop antenna which happens to be facing toward the front of my bench.
:
:I was about to start work on a Zenith 6d-614 which also has a type of square-box-shapped loop antenna too.
:
:As I pulled the Zenith out of it's case I set it down near the Bendix 525 such that the two antennas just happened to be about 2 inches away from each other.
:
:Now the Zenith is without power, yet as the two units came close... the Bendix suddenly went up almost double in signal and output!
:
:As I positioned the Zenith further and nearer I found that the the optimum distance is just about 2 inches. I tried rotating it in various angles as well yet 2 inches and straight aligned was the optimum.
:
:... but the real interesting thing was... that I found that the Bendix signal got even stronger as I "tuned" the Zenith dial (no power) to the SAME station as the Bendix.
:It was so funny tuning the un-powered Zenith and listening to the Bendix volume go up and down!
:
:Just having an RF-only-powered antenna-tank-circuit in close proximity coupled it's signal right over from it to the other antenna.
:
:I don't know what I learned here yet lol.
:... perhaps that double antennas work better than one?? lol
:I don't know. All I know is I just discovered it and I'm repoting back to headquarters here...

7/23/2006 9:15:03 PMPeter Balazsy

Thanks.. marv and norm but why do you say there was not increased gain?

Maybe I am not using the word 'gain' properly?

I didn't mean to split hairs over the use of the word 'gain' since I was just marveling at the improvement, "gain" or whatever you call it that was caused by the proximity of the two antennas.

By sharpening the tuning it must effectively produce a higher value of RF signal voltage signal somehow ...
....And then isnn't that creating greater 'gain' from the antenna circuit as it appears to the input of 1st mixer/osc Rf amp? ... no?
Doesn't greater RF signal from an antenna tank circuit equate to greater gain? Or does "gain" only relate to the amplification factor of an active circuit?

I would think that if the volume got way louder at the audio stage ...then somewhere somehow... there was a signal 'gain'... no?
...if adding the other non-powered tuned circuit in close proximity to the powered unit created the volume increase effect by sharpening the antenna tank circuit in the powered unit... there must have been some actual greater signal present at the first stage... so... wasn't there some improved signal or greater "gain" coming from the antenna?

7/23/2006 10:47:23 PMMarv Nuce

Peter,
You're absolutely correct that the RF signal level does increase, and thats why I used the term "apparent" gain as opposed to gain by amplification. In antenna theory, gain of a given device is referenced to the perfect dipole, and the perfect dipole being a non powered/inactive device has no real gain, but gain of a multi element device will exhibit several db (apparent) gain referenced to the dipole, and hence the additional rise in RF level at the active receiver loop is apparent gain.

marv

:Thanks.. marv and norm but why do you say there was not increased gain?
:
:Maybe I am not using the word 'gain' properly?
:
:I didn't mean to split hairs over the use of the word 'gain' since I was just marveling at the improvement, "gain" or whatever you call it that was caused by the proximity of the two antennas.
:
:By sharpening the tuning it must effectively produce a higher value of RF signal voltage signal somehow ...
:....And then isnn't that creating greater 'gain' from the antenna circuit as it appears to the input of 1st mixer/osc Rf amp? ... no?
:Doesn't greater RF signal from an antenna tank circuit equate to greater gain? Or does "gain" only relate to the amplification factor of an active circuit?
:
:I would think that if the volume got way louder at the audio stage ...then somewhere somehow... there was a signal 'gain'... no?
:...if adding the other non-powered tuned circuit in close proximity to the powered unit created the volume increase effect by sharpening the antenna tank circuit in the powered unit... there must have been some actual greater signal present at the first stage... so... wasn't there some improved signal or greater "gain" coming from the antenna?

7/23/2006 11:55:19 PMDavid

Is this how a Select-A-Tenna AM Radio Antenna made by Crane works?

7/24/2006 12:24:28 AMMarv Nuce

:Is this how a Select-A-Tenna AM Radio Antenna made by Crane works?

7/24/2006 12:30:45 AMMarv Nuce

David,
I'm not familar with the device you noted, but if the design/application is similar in nature to the earlier noted discussion, yes.

marv

:Is this how a Select-A-Tenna AM Radio Antenna made by Crane works?

7/24/2006 1:04:58 AMThomas Dermody

Yeah, that's how it works. You're talking about the big circular thing that's nothing more than a loop with a tuning condenser.

T.

7/24/2006 10:17:45 AMRMeyer

Terk sells a loop with a tuner in it for AM that does this also.

7/24/2006 10:20:49 AMplanigan

Pete, check mindspring.com/loop-antenna, the site has loop antenna designs and points out that even in close proximity to set (not physically connected) they work. What you were doing was adding a loop antenna to the operating set. Pat

7/25/2006 2:23:32 AMPeter Balazsy

Yes Pat.. I see that... thank you...
It was just kinda nice to hear one radio get really louder by just placing another radio on the becnh near it.. I guess I just never noticed it before