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| I agree with Kevin. I also have no xpdr issues using the carbon as a ground plane. The nav/com/xpdr/gps frequencies are plenty high to insure good capacitive ground coupling to the carbon. The resistance of the carbon is plenty low for RF purposes.
John... Don't know where your xpdr antenna actually is. If it way forward at the firewall station the problem may be interaction with the propellor. Just a guess at this point. The prop blades passing near the xpdr have been identified as the issue on other installations I saw in the early days. Mine is located just behind the spar box on my IV with no ground plane or problems.
Jack Morgan On Nov 6, 2013, at 6:01 AM, Lancair Mailing List wrote: Subject: TXPDR Antenna and such
Date: November 5, 2013 11:58:13 AM EST
For what it is worth, I'm using the carbon as my ground plane.
I've been on a couple of cross country flights and the only thing ATC is having trouble with is the noise in the cockpit. I suspect interior and such will absorb some of that noise when I get to it. Otherwise they are getting 5x5 on the signal quality (or at least that is what they are telling me when I ask).
Both the TXPDR and communications seem (thus far) pretty clear trouble free.
I decided not to put on an additional ground plane because the resistance of the carbon, while worse than copper or aluminum, is still pretty decent. I took a chance and it seems to be working out so far.
Perhaps at some point I'll be proven wrong, but I think it is worth discussing and trying to quantify.
Kevin
N969RJ (flying)
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