Marc Ramsey wrote:

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


I don't believe they transmit at all, unless they receive a radar
signal. Perhaps Eric or others more knowledgeable than I, know...

I've never read that or heard anyone suggest that before, so I really
doubt it. They were designed long before the passive "alerter" units
became available, which are the only instruments I know of that might
benefit from it. Perhaps someone with a TPAS, Surecheck, etc could tell
us if their unit gets a signal from their airplane when it's in the
hangar and the transponder clearly isn't getting hit by radar?

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Eric Greenwell
Washington State
USA