wrote in message
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Continuing problems seeing ATCRBS transponders with Mode S
interrogators

Hey all, I work in, lets call it 'an associated industry' and we are
still seeing ATCRBS transponders that reply to some interrogators, and
not to others.

At one time this was known as the 'P4 problem', sometimes as the
'Terra problem', just want to ask if anyone out there flying with an
ATCRBS xpdr is still having trouble being 'seen' by some
interrogators, but no problem with others.

You need to provide more symptoms, locations, interrogator identifiers, etc.

Some types of interrogators have the ability to selectively interrogate
ModeS transponders (although I'm not sure if any of them do in actuality).
Early on in the ModeS program there were sensor problems with side lobe
suppression and reflection rejection, although those problems may have been
addressed with later modifications. This is my best guess as far as to what
you're referring to, although it would actually be more correctly referred
to as a "P2 problem" although I've never heard it called that.