Warning to users of Zaon PCAS MRX

On Feb 21, 10:53*am, JS wrote:
The electronic technology isn't there yet.
* Who wants "the boy who cried WOLF" in the cockpit, or the need to
consider whether you're being interrogated by RADAR for the thing to
work?
* Something akin to the Swiss unmentionable-on-this-forum device is
needed in all aircraft.
They fail too, mostly due to bad antennas. But at least you know it
when the towplane or the glider launching after you are not on the
visual display.
Heads up!
Jim

On Feb 20, 3:02*pm, Bruno wrote:

I have had
plenty of alerts when the target is at the same altitude as myself
when the unit is working. *This includes my towplane and other
aircraft in the same gaggle (circling with the air force gliders at a
contest near radar). *In normal operation you never pick up yourself
if you have a transponder.

Bruno - B4



Jim

The false alarm/"boy who cries wolf" problem like what Andy is
describing appears to be very rare with the Zaon MRX. My experience is
if the MRX warns of a threat you get your eyes outside looking for it.
It is (literally) eye opening how much stuff an MRX can find that you
might otherwise miss.

All these traffic awareness technologies, including Flarm (there I
said it!) have limitations. The main limitation with Flarm is not
having a magic wand to wave to get Flarm units installed in other
aircraft, and many of those other aircraft have transponders today.
And while it would be great to see things like PowerFLARM (PCAS, ADS-B
1090ES data-in and yes FLARM!) installed in the USA glider fleet, I
expect you will never be able to convince a significant number of GA
aircraft in the USA to have Flarm anything (including combined
products like a PowerFLARM).

Darryl


Darryl

On Feb 21, 6:04*pm, Darryl Ramm wrote:
On Feb 21, 7:02*am, Andy wrote:



On Feb 20, 10:10*am, kd6veb wrote:

Hi Gang
* This thread prompted me to think as to how the MXR unit ignores my
transponder in my glider which is being pinged regularly where I fly?

As Darryl has explained the MRX is designed to distinguish between
your own transponder and the transponders of threat aircraft.

However in my PA-28 the MRX seems to get confused at least once on
every flight, usually about 10 minutes after takeoff. *What happens is
that I see a target rapidly converging on me in both altitude and
distance then it stays about 0.6 miles from me at the same altitude.
If I cycle power on the MRX the target, which was my transponder, goes
away usually for the rest of the flight.

I adjusted the suppression level but still have not eliminated the
problem. *I know that my transponder is a bit low on power until it
has been responding for about 10 minutes and I assume this is
contributing to the problem. *It's a bit puzzling that, before the
spurious target converges on me, the MRX reports my own transponder
squawk and pressure altitude correctly. *This would seem to imply that
the spurious converging target is not the first acquisition of my
transponder signal.

I have not sent the MRX back to ZAON for testing since I thought the
problem may have been caused by a detuned aircraft transponder
antenna. *It is missing tip ball. *After a bit of investigation I was
able to obtain the manufacturer's drawing of the tip ball and found it
was made of acrylic, not brass as I had assumed, *so it would not have
been a factor.

Substitution of a different KT 76A would be the next thing to try but
I don't have a spare just lying around

Andy

Andy

I would suspect other things before the transponder itself, including
the antenna and encoder. Does the MRX see a local ghost in other
aircraft? If so obviously I'd suspect the MRX more and want to get it
checked, or that may point to the MRX not seeing enough transponder
signal in your PA-28 to reliably pick it as a local transponder.

One test is to hit the local mode button on the MRX when this happens
and see if the MRX is using the local transponder for altitude or not
(a job for a front seat PAX... don't crash into a real threat while
doing this!). If it is then one explanation (grasping at straws
here...) could be that you are seeing strong ground reflections with
enough time delay to look like a second transponder. But in that case
I would hope the relative altitude to be fairly consistently around
"0.0" (or possibly garbled unintelligibly/ignored ?) but there could
be complex reasons while the relative altitude does not exactly report
within +/-"0.1".

The problem is the MRX not seeing enough local transponder signal. You
might try moving the MRX to a different location on the glareshield
and see if that makes this happen less. Keeping the antenna clear of
metal structures.

If the transponder antenna was hit/bumped and that caused the ball to
break off be careful that there was no other damage internally that
could affect radiated power esp. if somebody had to bend the rod
straight. The ball being plastic is a bit strange. I'd find an all
metal one next time.

Another thing is just to try to confirm that the MRX internal altitude
and the encoder altitude are close. *The KT 76A does not display your
encoder altitude and the MRX will show you its altitude not the
transponder altitude if it thinks the transponder is not local so
there is no simple way to really check this for sure. (You wanted to
replace the KT76A with a GTX 330 or TT-31 anyhow right?). But if you
see a threat that is not mostly at +/- "0.1" or so relative altitude
then maybe altimetery is more likely a suspect. When you say that the
altitude of the ghost threat gets closer how much relative altitude
error does it start with and how close does it get? How smoothly? Any
idea if at that time your transponder is being continuously
interrogated?

The MRX internal altimeter measures cockpit ambient pressure and your
transponders/encoder is measuring aircraft static. You might just be
getting unlucky on climb-out or other things (like opening a cockpit
vent, or effects from the encoder heater cycling) that pops the
encoder and MRX altitude just far enough apart, especially if there
was already a baseline error, that causes the MRX to think your
transponder is no longer local. There are several ways how I could
wave my hands to explain a ghost target that might appear at a
changing/converging altitude, but they would be just wild-ass guesses.
And you also might need to throw in real threat aircraft that you
never actually see into this picture.

Unless the aircraft is IFR equipped the encoder accuracy is not
usually tested during the biannual transponder checks. However the
encoder operation would have been checked when it and/or the
transponder was installed). *The RF output power and signal is tested
in the biannual tests however. Obviously any other problems or
strangeness with the static system could be a culprit here--what
happens if you pull the alt static in flight? What altitude difference
do you see? (at different airspeed/vents open/closed etc. ?)

Anyhow a long-winded way of saying I have no idea what is really going
on :-)

Darryl


Grr I meant to type... "*If* the problem is the MRX not seeing enough
local transponder signal. You might try moving the MRX to a different
location on the glareshield and see if that makes this happen less."

On Feb 21, 7:04*pm, Darryl Ramm wrote:

The ball being plastic is a bit strange. I'd find an all
metal one next time.

Yup, I was surprised too but this seems to be Piper original equipment
fit and the TED antenna, which is now obsolete, was mostly fabricated
by TED but has a ball end and mounting disk (washer) supplied by King
(now Honeywell). The current model TED antenna has a brass ball end
but it does not fit the hole in the aircraft. I chased down the
drawings so I could buy a brass ball and drill and tap it to fit the
antenna. That would have detuned it and probably made my problem
worse.

I had a private email from an MRX user who had experienced a similar
spurious threat problem. In his case it was caused by a
malfunctioning MRX baro sensor. I can see that if the sensor
originally tracked the local transponder alt and then stepped off and
drifted back it could cause the symptoms I see.

Part of the difficulty is that I have been chasing multiple problems.
The really critical one was that my encoder was thousands of feet in
error when cold. That was fixed a while a go by buying a new one but
proving it was the problem required making an encoder test box and
running some cold soak tests. (I reported on that earlier).

ZAON customer sircice has been helpful and suggested I send it back
for testing but, being a stuborn engineer, I want to characterize the
problem first

Andy

On Fri, 19 Feb 2010 09:53:50 -0800 (PST), Bruno
wrote:

I have now had my unit fail twice without any indication of failure.
It still seemed to be working fine until I saw a jet whiz by real
close and realized that I hadn't had any alerts for a flight or two.


Flarm and compatible units may develop a very similiar fault.
These devices will show no apparent sign of malfunction, though they
have become almost "deaf".
The cause seems to be in the damage caused by static charges in the
receiver circuit; the antenna probably gets the static from the
plastic canopy. Or maybe from the pilot itself (especially after
touching/cleaning the canopy on a dry day).

send the unit back for repair, if it doesn't spot other gliders in
flight (known to have a flarm on board).

Unfortunately, ground testing isn't conclusive, as the damaged
receiver still gets messages from nearby gliders (less than 50-100
meters).

Aldo Cernezzi