Nice summary of the PCAS models available. Airliners and some corporate
jets have TCAS; they can "see" you without having to be told by ATC.
Smaller motorized traffic likely do not have TCAS; they need to be in
contact with ATC to know that your transponder-equipped glider is
nearby.

My choice was the Zaon MRX. Small, small, small. I run it on the
rechargeable batteries recommend by Zaon (multiple flights per set of
batteries). This model gives relative altitude, altitude trend, and
distance. And its beep beep is cheap cheap.

It does not give azmuth information, but it has forced me to improve on
the good old-fashioned rubber-necking see-and-avoid procedure. One of
the advantages of the MRX is that the alerts are audible; we already
have too much heads-down technology in gliders to install more
equipment that requires visual monitoring.

When my MRX gives two beeps, I start looking everywhere (mine is set to
beep twice for traffic within 1NM and 1,000 feet). When it advances to
four beeps, I start looking everywhere with super motivation (mine is
set to beep four times when traffic is less than 1NM horizontal and 700
feet vertical).

Portablility is an added advantage of the MRX. When doing intoductory
rides for our club, I take my MRX unit with me.

The advantage of PCAS over the transponder is that you, the glider
pilot, is alerted to all traffic with transponders. This includes
Cessna 152s, corporate jets, commuters and large airliners. If all I
had was a transponder, I would have to be in communication with ATC and
under radar coverage to be available to be told about other traffic.

Airliners with TCAS are able to see transponder-equipped gliders and
react. But, small powered aircraft cannot electronically see those same
gliders unless those small powered aircraft are communicating with ATC
(in a radar environment).

PCAS (portable collision avoidance system) gives me more peace of mind.
Given the choice between only some of them being able to see me, or me
being able to see most of them, is the main reason I chose the MRX over
a transponder.

Last week, I had a couple of "two beep" alerts. Both of these aircraft
came up from behind and below. But I was able to spot them sooner that
when I did not have the MRX.

But when Santa Claus comes with money, I'll have both a PCAS and a
transponder.