I now have several flights in after mounting my H antennas external. My H is pretty solid for the most part and I have had no major issues since the upgrade.
Standing near the H I can raise and lower the gear with zero glitches. I have noticed a couple times if I'm in my vehicle where the ST16 may not have the most direct link to the H and I operate the gear there can be a momentary glitch.
The glitch only seems to happen when the gear is in motion. This makes me believe it is some kind of RF or noise from the retract motors in action. Orientation does not seem to matter only the gear in operation.
Thanks for posting, I completely agree with your thoughts about what might be going on.
While I haven't noticed video link glitching specifically when the retract motors are in action, I haven't systematically looked for it yet either. Now that weather on the US East Coast is not so conducive to frequent flying, it might be time to do some safe, legal range testing (aircraft on but not actually flying). If I can figure out a way to have someone hold the YTH (with no props obviously) in a manner that permits gear actuation, it would be interesting to see if glitching occurs when there is substantial distance between the ST16 and the aircraft. I would think that susceptibility to RF interference would be greater when the SNR is reduced (by distance), and so this admittedly atypical setup could help determine whether operation of the retract motors can reliably produce glitching. I have not yet attempted any modifications to the aircraft antennae, but that may be on my list for winter upgrades.