from ethe Surecheck website http://www.surecheck.net/avionics/#
The new TrafficScope models contain the latest third-generation TPAST
(Traffic Proximity Alert System) technology. TrafficScope listens for
transponder replies from all aircraft within the detection window and
derives altitude and range information on-the-fly. When target aircraft are
interrogated by ground radar or any other active system, such as TCAS, the
transponder responds with range and altitude (Mode C) information.

TrafficScope also listens to your own transponder to establish a base
reference. Since virtually 100% of the US and most outlying airspace falls
within radar coverage, aircraft can be detected with a great amount of
certainty.
tim




From: "Andrew"
Subject: TPAS (was Proxalert R?)
Date: Tuesday, February 10, 2004 12:37 PM

Hello,
Mode A and C transponders only transmits when they are interrogated.

Concerning anticol devices; i fly with a Proxalert R5 and this guy is
impressive. It's much more useful than the Surecheck devices. It's the
ONLY device to display SIMULTANEOUSLY up to three threats info
including squawk code

Andrew

(Mark James Boyd) wrote in message
news:40287949$1@darkstar...
Tim Mara wrote:
as far as I know transponders do transmit even when not being
interogated.they just don't reply with as strong a signal and not as
often
tim

Transponder: transmits as a response? As far as I know, they
only transmit when interrogated (at least the OLD ones did).