Comm Antenna Spacing

I'm looking for guidance on dual comm antenna spacing. ie. What has worked for some of you? Can the bases of two comm antennas be as close as 24 inches with acceptable results?
I checked the aeroelectric forum & basically found "keep them as far apart as possible/practicle".
I appreciate any help on this.

Sam
7A_@ABI

Interlock good enough and why?

I am not sure if it is a matter of cutting performance of the adjacent antennas or somehow damaging the other radio with to high RF signal with close spaced antennas.

However in regards to doing radio damage I was helping a guy with a dual ICOM A200 installation and it appears there are pins to LOCK out or interlock the transmit/receive of two radios. In other words when you transmit on one, it shuts down the receiver of the second idle radio. It makes sense and no doubt is common. I know the my transponder had a "strobe" that interconnects to a DME (if I had one) so they are synced to not interfere.

I think you answered your own question. If it was up to the radio antenna engineer the would have you put them on opposite wing tips, but for most of us, far as practical is good enough. For the RV the best spacing would be one on the fuselage top behind the cabin and another on the belly under the seats legs. Have fun. I am pretty certain you can put them both on the belly with 2 feet. I stand to be corrected.

George

Comm antenna spacing

If you can, put one on the bottom and one on the top. They work really well this way. The lockout method George described will work, but the PS Engineering intercomms (and most likely some of the other intercomms as well) have a feature where the pilot and copilot can talk and listen on SEPARATE frequencies at the same time. I've used it a number of times while airborn. It comes in really handy sometimes.

Vic

My com antennas are on the bottom of the fuselage just forward of the main spar (RV-6) at each side. They work fine. Rule of thumb is no closer than the length of the antenna. Of course the farther apart, the better.
Mel...DAR

The antennas on my Skyhawk are 8" apart came from cessna that way . I had the plane for seventeen years never a problem.

Jim G

Here's the general scoop: If your antennas are too close to each other, you can screw up your VSWR. The antennas will interact with one another. Maybe it's ok...maybe it's not. If you look around you may find references to output amp damage occuring but I SUSPECT that this is occuring for the same reason lots of output stage radio damage used to occur...high VSWR. Without getting technical, hi SWR's beat up on the output stages of your radio.

Some newer radios protect themselves against damage (so that's probably OK), but you could hurt the performance of the antenna (there are a million ways to hurt your antenna's performance, though...this is just one of them). It doesn't nescessarily mean that you will hurt the performance and also consider that you probably don't need max performance. Somewhere in there is a "good enough".

The VSWR is an excellent measure of your antenna's performance (i.e. all the energy you're throwing into the antenna is radiating as opposed to "bouncing" back and heating up your radio). Regardless of how you mount your antenna's, it's a good idea in general to check it out with a meter and be prepared to tweak. I'm guessing that lots of people will disagree with this, and that lots of planes are flying that have never seen a VSWR meter and have absolutely no radio problems whatsoever. If you're at all concerned about your installation, though, there's an easy way to check it with the meter.