Overthinking dual comm antenna location

I'm installing two bent whip VHF antennas, 8" behind the spar, in my RV7.

Some have mounted these in the outside bay (37" spacing).
Others have mounted in the next bay toward the center (28"spacing).

Both locations seem to work, though one report in the archives suggest some cross-talk at the closer spacing.

Normal recommendation is as far apart as possible, with an 18" ground plane. Locating in the outer bay leaves only 5" to the edge of the bottom skin.

Any thoughts that would break the tie, and relieve my indecision?

Stein told be 3 feet from tip to tip. I mounted mine in the first, outer bay behind the spar, with the front screws into the spar flange - bad idea! The forward lower skin stops there and presents a step for the mounting surface. A little further aft would be better. I had to separate the transponder and ADSB antenna, my comms are in the middle.

I think the back of this bay would be good. I actually read the official doubler requirements and tied mine to the rib and runner.

Depending on your radios, cross talk may be mitigated by the wiring of the "transmit interlock in/out" between the radios. Some of newer radios have this.

Use the outer bays, more hole options in the carry through, antennas furthest apart. Use a piece of .025 about 6" wide across each bay, long enough to rivet between the bottom skin and ribs - just like the wing walk reinforcements from which you obtain the needed scrap. Position the antenna further aft, towards the seat pans' overlap, than the pictures above. You'll want those plate nuts out of the way when you drive in the wing bolts. The wing adds to the ground plane of the fuse.

John Siebold

I put my antennas in the second bay inboard from each side. I had too much wing wiring/coax going through the outboard bays. No "cross-talk" issues or interference issues to speak of, including when in split mode using both radios at the same time. I have a GTN-750 and GNC-255A.