Warning to users of Zaon PCAS MRX

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 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 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 Feb 20, 11:43*am, Darryl Ramm wrote:
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

I don't own one of these yet, but I just have to ask this question.

Are you saying if a target is at the same altitude as you, it will be
suppressed? That is a scary thought! I would think the horizontal
proximity would also be part of the suppression criteria.

On Feb 20, 3:21*pm, Westbender wrote:
On Feb 20, 11:43*am, Darryl Ramm wrote:



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

I don't own one of these yet, but I just have to ask this question.

Are you saying if a target is at the same altitude as you, it will be
suppressed? That is a scary thought! I would think the horizontal
proximity would also be part of the suppression criteria.

I don't want to speak for them but the answer is no! 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

On Feb 20, 2:21*pm, Westbender wrote:
On Feb 20, 11:43*am, Darryl Ramm wrote:



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

I don't own one of these yet, but I just have to ask this question.

Are you saying if a target is at the same altitude as you, it will be
suppressed? That is a scary thought! I would think the horizontal
proximity would also be part of the suppression criteria.

I expect this could happen if the threat aircraft manages to fly
around with you for some period of time while while maintaining
altitude (within ~100's of feet?) and presumably with a roughly
constant (and high?) received RF power from the transponder, and there
no other signal that looks more like your own local transponder (if
you have one). I expect the only time this is a practical issue is
when you are formation or buddy flying pretty close by another glider.
But if you are close to another glider or gliders anyhow PCAS type
solutions are not of much use (you already know the other guy is there
and just seeing him on the PCAS may mask other threats, which would
not be not good). In fact going quiet after a while about the buddy
threat might be a feature. If altitudes are very close for long
enough I would not be surprised if there are cases where the MRX
would drift in and out of thinking which transponder is local. And
again if both aircraft have transponders it is unclear what any PCAS
will do if there is bad synchronous garbling. (I should have pointed
out before that it is obvious that the MRX can handle some garbling).
Possible things could include the Zaon misreading both transponder
altitudes, in which case it would reverting to its internal altimeter
and possibly showing no threats (because garbling makes it thinks
there is one transponder at some bogus altitude).

If the garbling is not an issue I would hope that a few hundred feet
altitude change or change in RF power that might be seen when circling
would be enough to break the "local" transponder association. But
again I don't know.

The MRX clearly has some smart algorithms that does this self-threat
elimination. I expect it looks at RF power, and I am guessing that it
could also do other things like keep track of your squawk code and
reevaluate if that appears to change (but this may be unreliable since
won't interrogate Mode-A). Again the exact algodithms are not
descibed. A threat coming at you exactly at the same altitude
absolutely should get picked by the MRX as a threat. I've proven that
several times...

Again the Zaon MRX appear to work very well to enhance traffic
awareness and I highly recommended them, but as always some ideas
about the possible limitations of all these types of devices is
useful. And lets not forget that "see and avoid" is pretty limited as
well.


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 20, 3:02*pm, Bruno wrote:
On Feb 20, 3:21*pm, Westbender wrote:



On Feb 20, 11:43*am, Darryl Ramm wrote:

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

I don't own one of these yet, but I just have to ask this question.

Are you saying if a target is at the same altitude as you, it will be
suppressed? That is a scary thought! I would think the horizontal
proximity would also be part of the suppression criteria.

I don't want to speak for them but the answer is no! *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

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

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