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On Sep 24, 12:21 am, "Mike" nospam@ microsoft.com wrote:
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.


This is a Mode S/ATCRBS interrogator, short P4 pulse on the ATCRBS
interrogations, certain percentage of the ATCRBS transponders are
visible to a nearby ATCRBS-only interrogator but do not reply to the
MODE S interrogators ATCRBS-ONLY ATCRBS interrogations.

The P4 problem was where an ATCRBS transponder would suppress on the
P3-P4 pair, mistaking it for a P1-P2 pair.


Before ModeS systems were commissioned this was a known problem and a ATCRBS
all-call interrogation was added to the ModeS systems (No P4 pulse). That's
why I'm asking you which sensor you are referring to because none of them
should have the problem you are describing, although some transponders may
still not reply to some ModeS all-call interrogations, they should still be
displayed due to the ATCRBS all-call interrogation from the ModeS sensor.
My understanding was the problematic transponders would be subject to an AD
and fixed, but I don't know if this ever happened.