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Re: [TowerTalk] Proximity of Antennas and Multi-Radios

To: "" <>
Subject: Re: [TowerTalk] Proximity of Antennas and Multi-Radios
From: "Jim Brown" <>
Date: Fri, 06 Aug 2010 12:02:47 -0700
List-post: <">>
On Fri, 6 Aug 2010 13:19:14 -0500, michael morgan wrote:

>Any guidance or advice would be much appreciated.

First, no contests allow operation on 30M, 17M, or 12M. 

As to isolation, beginning with simplest, and moving up in 
complexity, benefit, and cost.

1) Put the antennas as far apart as practical, and at right angles to 
each other. 

2) Avoid multiband antennas. They are better radiators and receivers 
of signals on the bands they are designed to cover.

3) Use robust common mode chokes on all feedlines at the antenna. 
This prevents coupling from one antenna to another via the feedline. 

4) Use good quality coax to feed all antennas. You can't choke a 
parallel wire line, so any imbalance in the antenna makes the 
feedline part of the antenna. 

5) Use coax stubs on each antenna to prevent coupling on harmonically 
related bands.  

6) Use bandpass filters on each transmitter tuned to the band you're 

There are two tutorials on my website that address this.  tells you how chokes work 
and the Cookbook gives detailed winding instructions and parts lists. 
They are VERY easy to build, and they work FAR better than anything 
you can buy for a lot more money.  includes a lot of advice 
about coax, and detailed instructions about stubs. Stubs are also 
inexpensive and easy to build. 

If you were a lot more serious than I think you are, I would point 
you to W2VJN's excellent book on Managing Interstation Interference, 
which you can buy for $20 from Inrad, the folks who sell crystal 
filters. It has a lot more detail than my stuff. It's well worth the 

First, you need to think about what kind of isolation, and how much 
isolation, you need. Since you're a casual contester, my guess is 
that you're NOT going to be operating both radios at the same time 
(that is, listening on one while you transmit on the other). If 
that's true, separation, good coax, and common mode chokes may be all 
you need to prevent one antenna from interfering with another 
antenna's pattern. On the other hand, if you DO want to listen on one 
radio while transmitting on the other, you'll need all six of those 
weapons in your arsenal. Contesters call this SO2R (single operator, 
two radios). Many top contesters do this. It is VERY challenging, not 
easy to learn, but can be a lot of fun.   

73, Jim Brown K9YC


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