What about what? What are you replying to?

I've covered this before but here is a recap -

ADS-B is a marketing fluff term. The details or exactly what "ADS-B" thing you mean are all important. A TT-21 cannot do 2020 Compliant (aka 14 CFR 91.227 compliant, aka SIL=3) ADS-B Out. It can do TABS/TSO-C199 (aka SIL=1) 1090ES Out with a TN72. And that lets all other aircraft with 1090ES In "see you ("any old GPS"/COTS aka SIL=0 installs are *not* seen by IFR/TSO-ed 1090ES In receivers), and if all the requirements for ADS-R are being met it also means UAT-In equipped aircraft see you.

FAA ATC controllers do *not* see TABS/SIL=1 aircraft displayed on their traffic displays, but they will see those targets via SSR if within range.

And I'll repeat my advice, it is stupidly simple: if buying a transponder today get a Trig TT22, it gives you all the option of Transponder only, TABS or full 2020 Complaint 1090ES if you want it in future.

A TT21 to TT22 upgrade is currently around $1k, the price difference between then when buying new is ~$125.

A TN72 GPS is pretty cheap ~$350 plus antenna, that any folks might as well add one to any TT21 or TT22 install. In an experimental glider with TT22 that can be configured for 2020 Compliance/SIL-3, all other configurations it can only be configured to do TABS. TABS gives visibility to airborne ADS-B receivers, makes gliders visible to PowerFLARM at much longer range than having PowerFLARM only, and makes the glider a client for TIS-B and ADS-R ADS-B In ground services (but that needs a TIS-B and ADS-R compatible receiver, which PowerFLARM is not currently).

Anybody installing a SIL=3 system with a TT21 risks a chat with the FAA. If a type certified glider, easier to track down and your A&P hopefully will not ever allow this. Yes I'm aware of legal arguments that you can do whatever you want if not intending to use to meet 14 CFR 91.225. Good luck with arguing that one with the FAA.

On Tuesday, October 15, 2019 at 6:08:27 PM UTC-7, Mike N. wrote:
What about adding a Trig TN72 to an existing TT21 transponder installation?

Will this combination provide ADS-B out?

Yes, I do already know that the TT21 is not certified for ADS-B out.

I have read some other threads about the TT21 being the same as the TT22 with the exception that the TT21 does not meet power output requirements for 2020 ADS-B output.
However I also read on a previous thread that originally ADS-B was supposed to be phased in 2 levels, and that the TT21 was made to be useable for the lower level of ADS-B out, and that level is no longer going to be an option.

So I am curious/ interested if the TN72 work in combination with a TT21 and provide ADS-B out, recognizable to local traffic, even if not a the required output wattage?