TT21 operation with no ICAO address

On Dec 9, 10:10*am, JS wrote:
* Does this mean that if the interrogator is not Mode S, the reply
will be downgraded to Mode C? From the book of Manuals, chapter 2,
verse 2.1:

The TT21 transponder responds to both legacy Mode A/C interrogations
and to Mode S interrogations from both ground radar and airborne
collision avoidance systems. In all cases, the interrogations are
received by the transponder on 1030MHz, and replies are transmitted on
1090MHz.

* The idea that the unit broadcasts more information and the fact that
many of us fly at higher altitudes than the TT21 is rated for has
caused me to order a TT22. The transponders I've used in the past had
no way to tell ATC what they were, so that wasn't a problem. I don't
care about the N Number being broadcast (when you first call ATC, they
have your number to associate with your Mode C discrete squawk code)
for any other reason than it could - in future - be a problem using
equipment outside it's certified environment. Easier to pay a couple
of hundred more thingies now and have it over with.
* The TT22 and certainly TT21 still use less power than, for example,
a Becker 4401-175.
* Regarding the price of Mode S transponder certification, in recent
experience it's less than recertification of the pilot!
Jim

Jim

Congrats on the TT22.

A Mode S transponder does not broadcast information about the device
power output. Technically the "class" describes the power output of
the transponder and that's just not transmitted AFAIK. Mode S
transponders do transmit (in the data register BDS (1,0)) detailed
information on all the many different data link things Mode S
transponders can implement (especially the high end ones used in
airliners etc.).

ATC cannot tell if you have a Trig TT21 or a Trig TT22 and they won't
care - the power output difference is really not significant in
practice. But if you want a TT22 to feel better about compliance with
regulation because you fly above 15,000' feet then go for it. The
important thing is to have and use a transponder where they are
needed.

And again to separate what _is_ really important - it is critical to
set up and use the correct Mode S/ICAO address for your aircraft
(issued to the aircraft by the FAA in its registration paperwork) on
any Mode S transponder at install time.

Darryl