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simple active antenna

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Mdkanz

New Member
I have an old FM tube radio that does not have a built in antenna. i has 2 plugs on the back for an antenna. is there a very simple active antenna that i could try? because if i just plug in wire it works but the reception is terrible.
 

ccurtis

Well-Known Member
I bought an active FM antenna several years ago from Radio Shack that worked well. Maybe they still sell it.

But, even a folded dipole made from 300 ohm twin-lead transmission line works significantly better than a piece of wire. It can be made, or purchased. Position it so it is perpendicular to the line of sight to the radio station(s) of interest.
 

marcbarker

New Member
Maybe the FM radio is out of alignment? There is a circuit near the antenna input in it that doesn't stay aligned. The double triode tube is also wears out, makes the radio low gain. The usual antenna for it is a 'ribbon aerial', with 2 wires one for each plug, and two arm thingies that you stretched out and attached to wall with nails or something.
 
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flat5

Member
For stereo reception you need an antenna that picks up the signal from one direction. Usually there are a few paths that the signal reaches your location. The phase differences from these various signals cause a mess at the phase detector that is trying to separate the stereo signal. You probably don't need an active antenna but a directional one. The simple 300 ohm dipole may solve your problem. If it does not work then try a yagi antenna.
 

MikeMl

Well-Known Member
Most Helpful Member
Little known is that most US FM stations transmit a substantial part of their effective radiated signal in the vertical plane. This is done because a large fraction of their listeners are in cars with vertical whip antennas.

I needed to put a FM broadcast antenna on my hangar, which is a totally-shielded steel box with a metal roof (no windows). I found that a simple vertical whip (~28 inches long) fed with 50 Ohm coax cable, using the existing metal roof as a ground plane works just fine with FM transmitters more than 50miles away.

I modeled a horizontal dipole (both straight and folded) and found that it would have to elevated several wavelengths above the metal roof in order to get low angle reception for the distant FM stations. At a height of less than a couple of wavelengths over an infinite ground plane, a horizontal dipole's major lobe is about 45degrees above the horizon. The vertical I ended up receives much more signal from a low angle...
 
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marcbarker

New Member
[multi-path reception] The phase differences from these various signals cause a mess at the phase detector that is trying to separate the stereo signal.
Really? I believe the radio is likely mono.
 
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