"JerryK" wrote in message ...
snip
The Monroy and other units will work in non-TIS areas with
aircraft with an operating transponder.

That's mostly true. It will work if someone is interrogating the
other plane's transponders. This usually means an area that has radar
coverage, or lots of TCAS equipped traffic.

I still fly in many areas out here in the west where I don't see the
reply light flash on my transponder for long periods of time.

John Galban=====N4BQ (PA28-180)