"Lakeview Bill" wrote:

My understanding is that older transponders used
something called a "cavity tube" that had a relatively
short life and was expensive to replace.

Supposedly, when the transponder was on "Standby"
the cavity did not age as much as it did when "On".


Where a cavity tube is used, "standby" does not extend the life of
the tube. On any xpondr, it merely inhibits any reply pulses from
being sent to the xmit section, be it a tube or transistors.

Fred F.