[TowerTalk] decoupling RF from control lines

[Pete Smith]

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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