Dean,

I just went through this with my IVP.
Considerations:
- a big round ground plane (radius on order the total length of the antenna) is nearly mandatory to really have it work.
if you can find two such areas on your belly that would be the optimal solution.
- diplexors involve substantial signal loss.  
- a switch is another possibility but that also is a reliability issue.

Given all that, I think my preferred solution is to totally optimize my number comm: no diplexors, no connectors, really good ground plane; and then do the best I could with a second antenna and use that for comm 2.   ...and provide myself a connector between the comm 2 antenna and comm 2 where I could manually plug in my portable instead of comm 2.

caveat:   I'm a total amateur and I'm sure this post will attract an expert opinion.

Colyn


On Dec 30, 2011, at 12:07 PM, Dean Whiting wrote:

I was looking for some advice about communication antennas.  The legacy is setup to have one com antenna.  We want a capable IFR airplane and I am hesitant to have one antenna with a diplexer (or is it duplexer, I've seen it both ways) as a possible single point of failure.  Is this the method that most people are using?  If you mounted a 2nd com antenna, where did you place it?  I searched the archives and found someone else who asked the same question but I couldn't find the answer.  Any other input or advice on the subject would be appreciated.

Dean Whiting

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