Last week, before the Minden midair, I reviewed Collision Avoidance
Systems with the intent of putting one in my transponder-less ASW-19. I
was interested in such a system because my glider club lies inside the
Mode C veil of PHL, because an active military air base is 5 miles
away, and because there are several airways that lie within several
miles of us. Here's the result of my research; I hope it might be of
help to others.

Zaon MRX - This was the one I bought. Pros - shows threat distance
and height; receives civilian signals A, C, S and 3/A, as well as
military signals X, Y and 2; alerts are visual and aural (high pitched
beeps); uses internal power (but can use aircraft power); is the
smallest system available; can be panel mounted with remote antenna.
Cons - does not show threat direction; doesn't output threats via
RS232 to PocketPC type devices. List price $499

Zaon XRX - This is the one I really liked. Pros - shows threat
direction as well as distance and height; receives civilian signals A,
C, S and 3/A, and also military signals X, Y and 2; alerts are visual
and aural (synthesized voice); outputs threats via RS232 to PocketPC
type devices. Cons - needs aircraft power; fairly large and tall, and
must be mounted on the glare shield. Supposedly Zaon will offer a panel
mount version with remote antenna in the future. List price $1795

Proxalert R5 - I rejected this one. Pros - shows threat distance
and height; shows squawk code of three threats (but threats combined if
same squawk); alerts are visual and aural (high pitched beeps); outputs
threats via RS232 to PocketPC type devices; can be panel mounted with
remote antenna. Cons - Combines threats with same squawk code on same
line showing closest threat distance, and flip-flops threat altitude;
needs aircraft power; only receives civilian A, C and S signals; fairly
large and hangs over glare shield lip. I also was turned off by the web
site, when I see poor English in sales literature I can't help but
wonder if the engineering was also done carelessly. List price $795

Monroy ADT-300 - I rejected this one. Pros - shows threat distance
and height (but only if you have an altitude encoding transponder);
alerts are visual and aural (synthesized voice); second smallest
available; can be panel mounted with remote antenna. Cons - Needs
altitude encoding transponder to show threat height; needs aircraft
power; only receives civilian A, C and S signals; doesn't output
threats via RS232 to PocketPC type devices. List price $795

Please note that this list is biased towards my own needs, in a quiet
glider with no transponder, operating with civilian and military
aircraft. You might have different requirements, so do check out the
manufacturer's sites for fuller specs and manuals:
http://www.zaonflight.com/
http://www.monroyaero.com/
http://www.proxalert.com/
A good single reference page to many Collision Avoidance Systems is
he http://www.avionix.com/collis.html
There are also some (fairly old) threads on RAS on this subject; you
might wish to search for them.

Be careful up there!

-John
(I have absolutely no connection or financial interest with any of the
companies named in this message).