I think there is a tad of over worry about all this, but following the
recommendations from the manufacture is almost always a good idea.
RV's are small planes and there are limited places to place antennas. With gear
legs, com antenna, firewall, wing spar, exhaust, there is only so much real-estate.
What ever you do will be a compromise. However you are not flying in the +FL180
altitudes, and your transponder will be able to communicate just fine with Mode C
RG-400 is pretty awesome stuff. I am not sure what Grarmin sells that cost more.
There are only so many 0.195 OD, 50 ohm, RF coaxials, and RG-400 is king (I thought).
RG-400 is a step up from RG-142 with solid core wire. RG-142 and RG-400 have
same performance for all intents and purposes. Solid wire is the only real difference.
RG-400 is what I used and try and minimize cable length, but 7 feet is not going to
ruin your transponders operations. 7 ft vs 6 ft adds 0.09 dB loss. Negligible. These
are all 50 ohm RF coaxial cables. They all "work" and it is unlikely it you would notice
differences in service. With that said see my first comment.
RG-58 is what was used before and performance and materials are less than RG-142
and RG-400. RG-58 has more loss. I would not use it for installation. However there
are many planes radios and transponders working fine with RG-58 today.
Raleigh, NC Area
RV-4, RV-7, ATP, CFII, MEI, 737/757/767
Last edited by gmcjetpilot : 10-28-2018 at 01:52 PM.