Warning to users of Zaon PCAS MRX

On Feb 20, 9:10*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?
Explanation anyone or a pointer to where I could find an answer to my
question? Thanks.
Dave

Dave RTFM! This is described in the manual. The MRX uses its internal
altimeter to compare to the Mode C altitude tramitted by an
transponder. If the values are close it assumes it is your transponder
it is seeing and supresses the alert. The exact logic/tollerances it
uses however is not described.


Darryl

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

On Feb 19, 9:28*pm, Eric Greenwell wrote:
Bruno wrote:
On Feb 19, 8:07 pm, Eric Greenwell wrote:

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.
Again, the unit turned on and seemed to be acting fine. *I sent it
back to Zaon and they were great and replaced the board to fix it the
first time.

Do you know if a failed unit like yours can still pick up the glider's
own transponder? If it cannot, that would give transponder equipped
gliders an easy way to test their MRX.

--
Eric Greenwell - Washington State, USA (netto to net to email me)

- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarmhttp://tinyurl.com/yb3xywl

- "A Guide to Self-launching Sailplane Operation Mar/2004" Much of what you need to know tinyurl.com/yfs7tnz

I have a transponder and no you don't pick up yourself. *After reading
Randy's reply I think this problem might be a little more wide spread.
Glad to be getting the word out. *Bruno - B4

OK, pilots with transponders can check their unit without needing
another plane around; of course, they still have be interrogated by
ground radar or a TCAS system within 10 miles or so (not sure what the
range is). If your MRX isn't picking up your transponder AND you can see
the transponder is replying, then the MRX is likely bad. Contact the
factory about it.

--
Eric Greenwell - Washington State, USA (netto to net to email me)

- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarmhttp://tinyurl.com/yb3xywl

- "A Guide to Self-launching Sailplane Operation Mar/2004" Much of what you need to know tinyurl.com/yfs7tnz

In case people don't know how to do this. Push on the multifunction
button on the left to get to the "Local" screen to see what the MRX
thinks is your local transponder squawk code and altitude, either from
the internal altimeter or transponder (read you user manual).

BTW it should be possible at least in principle for the MRX to know
the local transponder altitude but not the squawk code - e.g. if the
local Mode C transponder is being interrogated by an airborne TCAS
which make Mode C but not Mode A interrogations (so the transponder
does not get asked to transmit its squawk code. This might happen when
on the ground or at low altitude where there are no SSR
interrogations. Since the MRX is a black-box it's unclear exactly what
it does here. It would be interesting to check if the MRX can show
this situation outside SSR coverage.

If your glider does not have a transponder and your towplane does it
is possible that the MRX will think the towplane transponder is your
own (until you get off tow and the altitude difference between what it
thinks is the local transponder and its internal altimeter become too
large). It may also be possible that even if you have a local
transponder that the MRX still thinks the towplane tranponder is
yours. So you might see things like intermittent alerts that comes or
go or an alert for the tow plane once you get off tow, but not while
on tow.

It is also possible that the MRX (or any other PCAS unit) gets
confused by transponders both in the tow plane and glider replying to
interrogations (what's called synchronous garbling). TCAS (and SSR)
systems try to de-garble several overlapping signals like this but it
is unclear what the MRX can actually do there, if anything.

I think the MRX PCAS is a great safety/traffic awareness enhancement
and I've flow with them from soon after they were first available. I
have great experience with Zaon customer support. I broke my MRX
antenna off while swinging my leg over the top of my instrument
pedestal and I sent the unit in to have that fixed and have the unit
upgraded with a headphone jack and they did this a reasonable cost (I
can't remember exactly how much they charged) and they fixed the
antenna and also threw in a free spare one.


Darryl

On Feb 19, 9:53*am, Bruno wrote:
I have debated for a few months if I really should post this or not
but think I should share my experience. *First, I LOVE the concept of
the PCAS MRX and I have received nothing short of exceptional customer
service from Zaon. *I also would strongly recommend to every pilot to
purchase one of these fairly inexpensive units. *That said, I would
give them the following warning:

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.
Again, the unit turned on and seemed to be acting fine. *I sent it
back to Zaon and they were great and replaced the board to fix it the
first time.

A year or so passed and all of a sudden the same thing. *A plane flies
close by and I haven't had a alert for 5-6 flights. *I was closely
paying attention this time because of my last experience. *I sent the
unit back and, again, Zaon surpassed my expectations by replacing a
faulty filter this time, sending it back and not charging anything -
not even return shipping. *It was well out of warranty. *Wow! *Great
customer service Zaon.

I called and spoke with Zaon after this second fix. *When this
particular part fails on the Zaon PCAS there is no way for the unit to
tell that there is anything wrong. *It just doesn't pick up any
signals. *Therefore, it can't warn you if it is broken. *I would be
very surprised if there are not at least a few other units out there
that have this faulty part but the owner still thinks that everything
is ok.

Suggestions:
1. *See and avoid. *Don't ever rely on any instrument or other person
to watch out for other aircraft instead of doing it yourself -no
brainer.
2. *If your PCAS unit has not picked up an aircraft that it should
have you might want to consider it may have this problem.
3. *Fly far, land out every once in a while because you are pushing,
have fun and be safe.

Has anyone else had a similar experience with their MRX having
problems?

Bruno - B4

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