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Re: [TowerTalk] decoupling RF from control lines

To: "Jim Brown" <jim@audiosystemsgroup.com>,"towertalk@contesting.com" <towertalk@contesting.com>
Subject: Re: [TowerTalk] decoupling RF from control lines
From: Pete Smith <n4zr@contesting.com>
Date: Tue, 16 Aug 2005 09:21:10 -0400
List-post: <mailto:towertalk@contesting.com>
Thanks, Jim - The control cable I'm using is CAT-3 network cable.  In the 
TopTen convention, six of these lines go direct to the band decoder, where they 
are "sunk" to ground by the decoder.  The 7th and 8th are tied together and 
used for 13 volts out to the relay box.  The .1 caps were suggested by TopTen 
for best effectiveness at 160, but what I was really unsure of was the 
inductance of the RF chokes.  I'll certainly have a look at your app notes.

73, Pete  

At 09:06 AM 8/16/2005, Jim Brown wrote:
>On Tue, 16 Aug 2005 08:36:18 -0400, Pete Smith wrote:
>
>>I'm thinking that an RF choke in series and bypass cap to 
>>ground on each line would help.  
>
>Pete -- take a look at the following link, which is an applications 
>note I wrote for audio system RF suppression. The chokes described 
>would work quite nicely to suppress common mode current on those 
>cables. Simply use the data (curves) and guidelines to tell you how 
>many turns to use for the frequencies where you are having problems.
>
>http://audiosystemsgroup.com/SAC0305Ferrites.pdf
>
>Also look at the material in the link below on "the pin 1 problem." 
>
>http://audiosystemsgroup.com/Ferrites-Ham.pdf 
>
>You might also need capacitors, but probably a lot smaller ones. 
>
>Another point. Twisting can be just as important as shielding in 
>rejecting interference. If you aren't already doing so, and if the 
>right choke doesn't fix it, my next move would be to use cable that 
>uses a twisted pair for each signal circuit. 
>
>Jim K9YC
>
>
>
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>
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_______________________________________________

See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless Weather 
Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions 
and ask for Sherman, W2FLA.

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