My Zaon XRX PCAS just arrived. I did a test run last weekend (1/15) in
friend's pressurized Golden Eagle (Cessna 420) and Bonanza A36 in the
trip to Big Bear City, both planes have Garmin 530/330 TIS/Mode S
transponder (like 24Y's) for comparison purpose. I believe this
review is the first one you can find over the internet.

The Zaon XRX was first on the market on 11/31/2005, however, according
to my knowledge, the shipment wasn't begin till 12/15/2005.

XRX tracks up to 10 targets and displays the top 3 threats (in display
mode-A) on a LCD matrix display. It displays the threats direction (in
45 degree quadrant) , current altitude, climbing or descending, and the
estimated distance. The traffic is updated in real time. The good
thing about XRX is that it displays traffic not just in the terminal
area but any where within a radar coverage, and in area where TCAS
equiped airplanes in the vicinity (so surrounding aircrafts respond to
the TCAS interrogation). Mode-S transponder can only display traffic
information in terminal area (such as SoCal) because Mode-S receives
information from the terminal control radar that sends out the host
traffic information. For example, Mode-S cannot display traffic when
you fly out of SoCal basin...say on the way to Vegas but you are in the
center radar coverage. However, XRX relies on the target airplanes
with an operational transponder. If an airplane does not have
transponder turned on, XRX won't be able to track it. Mode-S will
probably display primary target (without altitude) because terminal
radar will probably depict this traffic in its TIS broadcast.

XRX contains 4 directional antennas (for traffic detection), a digital
compass for detecting the plane's heading (it can then correctly point
out the threat's direction). It also has a digital altimeter to
compare with the plane's mode-C transponder. That will reduce the
error caused by plane's shadow when you over fly water or some
reflective surface.

The Zaon XRX worked as advertised out of box. When we waited in the
hold-short line, I could see the 172 took off before us correctly
depicted on the XRX with its direction and altitude. When we took
off, the target airplane's directions was updated in real time and
displayed correctly. I would say its performance is comparable to a
Mode-S TIS system. When we climb out higher, however, because of the
pressurized cabin, the XRX thought we were still in 1000 feet so it
stopped displays traffic until I turned on the pressurized airplane
mode. In the pressurized cabin mode, XRX will only use the airplane's
transponder instead of use the built-in altimeter for its altitude
reference. When I flew back in the non-pressurized Bonanza, it
displayed the traffic correctly in the vicinity. The female voice will
warn you when a threat is closer enough.

However, there are several first look weakness in this test but I don't
think they are big issues:
1. It does not display the traffics behind the plane as good as traffic
in front of plane or on the side. I think it because the metal blocks
the rare view. XRX has a menu that allows you to select the type of
aircraft (composit a/c, high-wing a/c, low-wing a/c) so it estimates
more accurately. By comparing with the TIS, XRX tends to estimate the
distance closer than it is for the traffic behind you. However, I
don't think it is a big deal since most of traffic behind you has
little threats.

2. XRX does not remember the configuration setting after the power off.

Because of this, you have to re-select the type of aircraft everytime
you turn on the XRX. Also, you have to set the display mode if you
prefer to have Garmin 530-like radar screen (circle). And range,
warning distance..etc. It always resets to default setting everytime
it turns on. I think it is a bug in the firmware that cause it,
because XRX does remember many system settings such as altimeter
calibration and heading calibration values beyond the power-reset.
The good thing is that since Xaon supports the firmware upgrade, if
there is a firmware upgrade, you can send in the unit back and let them
upgrade the firmware for you. Another note is that XRX works well
with its default setting. Even without selecting the type of aircraft,
it still displays the traffic pretty well.

I think XRX is a very good and economical alternative of a Mode-S (one
third of price of mode-S, exlcuding installation labor). Since FAA is
no longer supporting mode-S TIS and is going to gradually disable the
mode-S TIS in the next several years, plus the XRX can detect traffic
over the non-terminal areas, XRX is a desirable choice until the FAA
fully deploys ADS-B in the next 10 years. It helps you a lot to
avoid the traffic since you can spot the traffic much easier.
Comparing to altitude and range only model (such as Monroy ATD-300), it
really is a break through of the portable passive traffic detection
system.

If you want to know what is PCAS, just goto their website at
http://www.zaonflight.com/