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Location for second com antenna

B

Bill Whitefield

Member
I will be adding a second com radio in the near future and seem to be very limited on the location of the second antenna. I have a 8A and the existing antenna is located directly below the rear passengers stick. It would appear that the only place to go is aft on the belly and stick with the bent antenna. Any alternatives?
Bill
 
My goal is to be able to monitor one radio while using the other. I fly out of a controlled airport that is under the class B and it is nice not to be fumbling around trying to grab the ATIS while talking to approach.
Bill
 
Aircraft Spruce sells a Bob Archer COM antenna for use in the wingtip. That would get you plenty of separation between your two antennas. Bob's antennas have been used on RV's for years. Just a small caveat: you have to follow Bob's installation instructions to the letter. The average Joe is going to dive off into the weeds by attempting antenna theory on their own.
 
I have two bent whip antennas on the belly of my RV-8 located aft of the main spar - perhaps 24” of separation. I use one or XMIT and one to monitor the standby freq on COMM #2. I have never had a problem.

Note - Comm #1 is the GTN-650, Comm #2 is the Dynon radio and I do not use a “desensitization” connection between the radios. Your results may vary depending on radio selection.

If you want to do a wingtip antenna I suggest you make one. Follow the general design from the AeroElectric book, but expand the leg going out from the wingtip as far as you can. Use an antenna analyzer to tune. You want the first third of the antenna to go from top to bottom of the wingtip as much as you can (as in as vertical as possible). The first third of the antenna is the high current part - so it does most of the work.

Carl
 
COM antenna separation and desensitization

What does it mean to «*desensitize*»?

I will install a second COM antenna on the belly of my RV6A tomorrow. I intend to use existing hole that was for previous transponder antenna. The two COMs (CI-292-2 antennas) would be 32 inch appart*?

Will this be acceptable? I checked tonight the setup on many Cessnas that have antennas above their cabins. They are from 36 to 39 inch appart… I know already that AC-43-13-2B specifies a minimum of 36 inch. I also know that Garmin specifies a separation of 6 feet from any other COM antenna (I am installing a GNC 255).
 
Some radios have a circuit that, when the other radio’s PTT is pressed, greatly lower the gain (sensitivity) of that radio, to keep the huge signal (due to being so close) from blasting thru.

OP: if you use a wingtip antenna, either bought Archer or build it yourself, be sure to follow Carl’s advice and get as much vertical throw into the leading edge as possible. It won’t be as good as an external antenna, but perfectly adequate for receiving ATIS.
 
One on top, one on bottom, I have the more powerful transmitter in the bottom antenna for flight use. The top antenna is certainly flight useable also but by habit I use it for ground operations and monitoring in the air. The top antenna is not subject to blanking by the landing gear on the ground which can happen although very infrequently (like 3 or 4 times in 1000 hrs)
 
rzbill said:
One on top, one on bottom, I have the more powerful transmitter in the bottom antenna for flight use. The top antenna is certainly flight useable also but by habit I use it for ground operations and monitoring in the air. The top antenna is not subject to blanking by the landing gear on the ground which can happen although very infrequently (like 3 or 4 times in 1000 hrs)
Click to expand...

How??? OP has an 8A
 
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