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).