Daryl,

First, I have no intention of equipping with ADS-B out and agree that there is little or no value to gliders. My interest in having a Trig that is compliant for ADS-B out is just in case FAA changes their mind and mandates it for gliders in 2020. Yes, the complexity of certification and cost are prohibitive. I'm just trying to consider whether it's worth it for an extra $300 and slightly higher power usage to be "ready".

My main interest is to protect myself against fast jets and airliners etc in busy airspace.

Thanks for all your explanations and background in this discussion... although it sure makes a decision on which unit to purchase difficult. I agree the TT21 is probably all I need for the time being.

Walt Rogers WX

If you fly in busy airspace, with airliners and fast jets etc. Please install a transponder. Whether it is a Trig T-21 or TT-22 has really no difference for the usefulness of that transponder. If you intend in future to go though all the money, complexity and hassle (uh why?) of installing ADS-B data-out as well then the question about TT-22 TSO-C166b certification may become relevant.