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dahugo

Member
Guys, finishing up an RV-9A. Will have two comms, an IC200 and Garmin 430W. Was planning on mounting both comm antennas on the belly between the wheels but the more I thought about it, the more I figured there may be some intermod or interference.

Anyone else put two on the belly side by side between the wheels? Pros and cons?

I'm thinking now that I will put one on the belly and one on top about midway between the tail and the canopy, with the GPS antenna just aft the canopy. Using two wing-mount (interntal) NAV antennas for NAV and GS, BTW.
 
That's where I've got the CI-122 Comm aerials for my GNS430W and SL30 on my RV-7.

I haven't had any issues at all with them in this location, on the ground or flying.
 
The counterpoise, ground plane, on these planes is not very long and as a result a 1/4 wave dipole antenna mounted on top of a plane will have its maximum radiation upward at 10-15 degrees and reduced radiation toward the horizon. Only mount an antenna on top if you're transmitting toward a satellite or if no other location is available. A wave-length at average comm frequencies is 93". Having at least 3/4 wave or 70" or more between antennas will reduce mutual coupling. If you want really good Tx-Rx, mount your antennas on the bottom of the wing at mid-chord just past the fuel tank.
 
Cessna mounts them that way...

Cessna has been mounting their comm antennas 3 or 4 feet apart on top of the cabins (152, 172,182, 206, 210, Caravans) since the 70's and I have never head of them having any problems with that particular installation.
 
A rough rule of thumb....

is that no antenna should be closer than the length of the longer antenna. In other words, if you have a 22" long antenna, no other antenna should be closer than 22" from it.
 
I agree with Mel on the spacing.
I would suggest one on the belly and on on the top. You will find some locations on the ground that you can not contact ground or tower with a bottom mounted antenna, if that happens you can use the top mounted antenna. In the air there is practically no difference in operational range.
 
sahrens said:
How far apart are your antennas under the wheels? I am planning to mount two under the baggage compartment. I think I have read somewhere they are suppose to be 21" apart.
Click to expand...

Mine are 29" apart, and I've had no issues (touch wood).

FYI, the GNS430W Installation Manual states "The antenna should be mounted a minimum of six feet from any DME or other COM antennas, four feet from any ADF sense antennas, and two feet from the 400W Series and its GPS antenna. The COM antenna should also be mounted as far apart as practical from the ELT antenna."
 
Mine are both on the belly............with no problems. A Garmin SL-40 & Icom A210.

L.Adamson --- RV6A
 
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