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Re: [TowerTalk] Nasty RF Problem. Advice Please

To: "Daron J. Wilson" <>,"'CARY GOOCH'" <>,<>
Subject: Re: [TowerTalk] Nasty RF Problem. Advice Please
From: Jim Lux <>
Date: Sun, 10 Sep 2006 11:40:53 -0700
List-post: <>
At 09:21 AM 9/10/2006, Daron J. Wilson wrote:

>In order to know the pattern of the FM antenna, you'll need to provide a
>good description, find the manufacturer and get some plots.  Generally, they
>are stacked elements which provides the gain, but there are numerous
>different designs.
> >
> > Now I don't know what an FM Stereo radiation pattern looks like, but
> > when I woke up this morning it occurred to me that if I had my
> > radio/antenna setup DIRECTLY below the FM setup, that I might have found
> > a null spot in the FM pattern? I think that if I can just clean up the
> > signal in this one antenna that we can live with the interference on the
> > rest of the gear.

And, while the mfr will probably have a good far field pattern, they 
may not have a good nearfield pattern, and you may well be in the 
near field.  And, even if you are in a null, that might still be a 
lot of power...

Say they're radiating 100W and you've got a 20dB null straight down 
where you put your stuff.  That's still like radiating a watt 
straight at you, which might be enough to foul you up.

Most transmitting antennas have significant lumps and bumps in 
directions other than desired one, and they'll be 15-20 dB down (or 
more).. but, considering it from the antenna manufacturer's 
viewpoint, they're not going to go to herculean efforts to turn a 
20dB null into a 30dB null.  The extra 0.9% efficiency probably isn't worth it. 


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