On Saturday, December 15, 2018 at 11:23:27 AM UTC-8, son_of_flubber wrote:
If you fly Experimental in airspace where you're not required to meet FAR 91.227 compliance, why wouldn't you configure your TN72 + TT21 to SIL=3? The only functional difference is that TN72 + TT22 (with SIL=3) puts out a stronger signal.

Because that is a violation of 14 CFR 91.227. Good luck with your next ramp check :-)

The reason for the FAA requiring high-power transponders to be used for ADS-B Out is to allow for the larger spacing between ADS-B Out ground stations.. The inconsistency that this is really required is awkward. If say ADS-R did not work reliably with lower-power TABS devices at longer distanced from ground stations that could be a dangerous by providing a false sense of traffic awareness/services being provided.

The Trig reply is a bit confusing as the situation has nothing to do with SSR radar per se. If the FAA really wanted to they might be able to profile suspected low-output power ADS-B Out sources. Possibly sitting on top of some technology already in the ADS-B ground infrastructure. But it would produce huge numbers of false positives. Maybe they just pick glider suspects. Or maybe they just ramp check all experimental gliders with SIL=3 ADS-B Out because of posts on public forums suggesting the possibility of violating 14 CFR.