Kirk,

I called up Zaon, and they said that the X and Y signal modes they
receive are indeed DME.

-John

wrote:
I thought of that, but think it's unlikely. TACAN is basically a UHF
"VOR"/DME equivalent, and is also used by civilians - airliners and
bizjets - and civilian DME is the distance measuring part of TACAN.
TACANs have both X and Y channels, Y being used for Air-to-Air distance
and bearing between cooperating aircraft (useless info: must set your
TACAN channels 63 apart to work: CH 29Y and CH 92Y are commonly used).
Anyway, only the DME portion transmits, the bearing portion is receive
only - like VOR. So it's unlikely that TACAN signals are being used,
in my opinion. If they are, then civilian DME should also trigger the
TPAS!