Darryl, I admit I oversimplified things. One of the reasons was that I
deal with analog ultrasonic signals produced by nature, not digital
pulse trains from transponders, so it made a first cut analysis easier
for me.

Hopefully Zaon will be willing to tell Eric what they're really doing
inside the box. Since I own a MRX and am planning on installing a
transponder, I'd be more than happy if my analysis at the start of
this thread is wrong!

Meanwhile, it sounds like you understand transponders, RF and digital
processing. Can you refer me to something on the web that would
explain the basics of how partially overlapped pulse trains are
differentiated? Using a stand-alone detector on analog signals of
similar frequency and fairly similar shape, I know I can't detect a
second signal 20-30 dB below an overlapping signal - so the
possibility you hint of for digital signals is outside of my
knowledge. Thanks!

-John

On Mar 10, 1:34 pm, "
wrote:
Also it is worth remembering the Zaon PCAs devices are not just
"blanking" the receiver during the local transponder reply. The Zaons
are reading and doing an altitude decode of the local transponder
signal and using that if possible for the altitude reference rather
than the built in altimeter. How good their RF front end and post RF
digital processing is will determine how well they can differentiate
partially overlapping pulse trains from the local and other
transponders. And you better believe they have to do this since the
most nieve approach of "blanking" during the entire ~20us transponder
pulse train (ignoring the ident pulse) would give a dead zone of
~6km. I'd love to see a schematic.. :-)

Like other posters I suspect this not much of an issue in practice
because of multipe illuminations from SSR, TCAS etc. However one thing
with some of the funkier glider tranponder antenna installs is that
the PCAS may be seeing much more RF power from the local transponder
than the designer expected, especially for situations like with RF
transparent fiberglass fueslages and maybe a less than great ground
plane betwen the PCAS and antenna, tranponder antennas mounted in the
cockpit etc. In which case maybe the dead zone is larger because of
the Zaon's reduced ability to detect overlapping pulse trains.

Darryl