MRX PCAS displays wrong code and altitude for my transponder

[5Z]

The MRX is mounted on top of the glare shield and the Becker is driving a L2 antenna mounted in the nose of my ASH-26E, just forward of the rudder pedals.

When I squawk 1201, the MRX shows 1236 (or other 12xx code) and the altitude is about 500' lower than what's on the Becker.

Are the antennas too close to each other?

I'm thinking of putting a sheet of foil just under the MRX and forward to provide some shielding from the xponder antenna. Since the MRX is attached to the glare shield, which in turn is attached to the canopy, I could also install a length of coax and place the MRX antenna by my shoulder on the canopy rail.

Thoughts?

-Tom

[Darryl Ramm]

On Apr 4, 10:19*pm, 5Z > wrote:
> The MRX is mounted on top of the glare shield and the Becker is driving a L2 antenna mounted in the nose of my ASH-26E, just forward of the rudder pedals.
>
> When I squawk 1201, the MRX shows 1236 (or other 12xx code) and the altitude is about 500' lower than what's on the Becker.

> Are the antennas too close to each other?

Yes. Even if this is not actually causing your problem (and I suspect
it is) this is a bad configuration.

An antenna around the rudder pedal area like this is not ideal, there
are too many conductive objects in the near field region of the
antenna and too many with dimensions likely to cause problems. The
best position is where the factory recommends and its not too hard to
do, but does require pulling the engine to access the engine bulkhead
interior to do the install. Well documented in a technical note by the
factory.

> I'm thinking of putting a sheet of foil just under the MRX and forward to provide some shielding from the xponder antenna. *Since the MRX is attached to the glare shield, which in turn is attached to the canopy, I could also install a length of coax and place the MRX antenna by my shoulder on the canopy rail.
>
> Thoughts?

Yes. Install the transponder antenna properly. :-O

You are bathing everything behind your panel in fairly powerful RF
pulses. If you want to install a PowerFLARM or other things later you
may find additional problem with that, besides its PCAS stuff not
working either. So instead of trying tinfoil bandaids I would start
again and do it properly.

>
> -Tom


Darryl

[Andy[_1_]]

On Apr 4, 10:19*pm, 5Z > wrote:
> The MRX is mounted on top of the glare shield and the Becker is driving a L2 antenna mounted in the nose of my ASH-26E, just forward of the rudder pedals.
>
> When I squawk 1201, the MRX shows 1236 (or other 12xx code) and the altitude is about 500' lower than what's on the Becker.
>
> Are the antennas too close to each other?
>
> I'm thinking of putting a sheet of foil just under the MRX and forward to provide some shielding from the xponder antenna. *Since the MRX is attached to the glare shield, which in turn is attached to the canopy, I could also install a length of coax and place the MRX antenna by my shoulder on the canopy rail.
>
> Thoughts?
>
> -Tom

First check that the internal baro sensor is set correctly.
Calibration instruction are in the manual. Then you can try adjusting
the suppression level. It's on page 2 on the calibration menus.
Call ZAON product support for help with that.

A local ASW-27 pilot has a TT21 with antenna mounted near the rudder
pedals and I have not heard him complain of problems with his MRX.

If in doubt send it back for calibration Mine had degraded to the
point it was useless and ZAON fixed it for me at no charge.

Andy

[Ramy]

On Apr 5, 10:21*am, Andy > wrote:
> On Apr 4, 10:19*pm, 5Z > wrote:
>
> > The MRX is mounted on top of the glare shield and the Becker is driving a L2 antenna mounted in the nose of my ASH-26E, just forward of the rudder pedals.
>
> > When I squawk 1201, the MRX shows 1236 (or other 12xx code) and the altitude is about 500' lower than what's on the Becker.
>
> > Are the antennas too close to each other?
>
> > I'm thinking of putting a sheet of foil just under the MRX and forward to provide some shielding from the xponder antenna. *Since the MRX is attached to the glare shield, which in turn is attached to the canopy, I could also install a length of coax and place the MRX antenna by my shoulder on the canopy rail.
>
> > Thoughts?
>
> > -Tom
>
> First check that the internal baro sensor is set correctly.
> Calibration instruction are in the manual. *Then you can try adjusting
> the suppression level. * It's on page 2 on the calibration menus.
> Call ZAON product support for help with that.
>
> A local ASW-27 pilot has a TT21 with antenna mounted near the rudder
> pedals and I have not heard him complain of problems with his MRX.
>
> If in doubt send it back for calibration *Mine had degraded to the
> point it was useless and ZAON fixed it for me at no charge.
>
> Andy

Folks, the MRX often displays wrong code and occasionally wrong
altitude. This is a common issue with this unit and nothing can be be
done about it. I recalibrated the threshold and returned my unit twice
complaining about it until they admitted this is normal due to design
limitations. The code and altitude usually gets messed up when flying
close to another glider and may stay wrong for sometime after that.
Just ignore the code. As for the altitude error assume a 500 feet
error so always search above and below you when it shows less than 500
feet difference.
My above comments are based on 5 years using this unit, multiple
correspondents with the factory and other pilots experience.

Ramy

[Darryl Ramm]

On Apr 5, 6:21*am, Andy > wrote:
> On Apr 4, 10:19*pm, 5Z > wrote:
>
> > The MRX is mounted on top of the glare shield and the Becker is driving a L2 antenna mounted in the nose of my ASH-26E, just forward of the rudder pedals.
>
> > When I squawk 1201, the MRX shows 1236 (or other 12xx code) and the altitude is about 500' lower than what's on the Becker.
>
> > Are the antennas too close to each other?
>
> > I'm thinking of putting a sheet of foil just under the MRX and forward to provide some shielding from the xponder antenna. *Since the MRX is attached to the glare shield, which in turn is attached to the canopy, I could also install a length of coax and place the MRX antenna by my shoulder on the canopy rail.
>
> > Thoughts?
>
> > -Tom
>
> First check that the internal baro sensor is set correctly.
> Calibration instruction are in the manual. *Then you can try adjusting
> the suppression level. * It's on page 2 on the calibration menus.
> Call ZAON product support for help with that.
>
> A local ASW-27 pilot has a TT21 with antenna mounted near the rudder
> pedals and I have not heard him complain of problems with his MRX.
>
> If in doubt send it back for calibration *Mine had degraded to the
> point it was useless and ZAON fixed it for me at no charge.
>
> Andy

Its not clear from this if the '27 has a dipole or stub/ground plane
antenna mounted here. One problem with an L2 style dipole antenna near
things like rudder pedals is they are more susceptible to conductive
objects. Moving the rudder pedals neat the antenna may even cause
problems (even maybe a Becker E10 error that I understand Tom has seen
at times in his install).

Its also just a bad idea to bathe all the other electronics in the
cockpit with strong RF signals from the transponder. You may get away
with it but its just not a good idea, and may cause problems that are
hard to track down.

Many manufacturers, including Schleicher, publish tech notes with
approved/recommended transponder installation procedures for a reason.
The Schleicher notes are well written and worth following, including
where to properly mount a transponder antenna, how to properly install
a ground plane etc.

Darryl

[Darryl Ramm]

On Apr 5, 6:43*am, Ramy > wrote:
> On Apr 5, 10:21*am, Andy > wrote:
>
>
>
>
>
>
>
>
>
> > On Apr 4, 10:19*pm, 5Z > wrote:
>
> > > The MRX is mounted on top of the glare shield and the Becker is driving a L2 antenna mounted in the nose of my ASH-26E, just forward of the rudder pedals.
>
> > > When I squawk 1201, the MRX shows 1236 (or other 12xx code) and the altitude is about 500' lower than what's on the Becker.
>
> > > Are the antennas too close to each other?
>
> > > I'm thinking of putting a sheet of foil just under the MRX and forward to provide some shielding from the xponder antenna. *Since the MRX is attached to the glare shield, which in turn is attached to the canopy, I could also install a length of coax and place the MRX antenna by my shoulder on the canopy rail.
>
> > > Thoughts?
>
> > > -Tom
>
> > First check that the internal baro sensor is set correctly.
> > Calibration instruction are in the manual. *Then you can try adjusting
> > the suppression level. * It's on page 2 on the calibration menus.
> > Call ZAON product support for help with that.
>
> > A local ASW-27 pilot has a TT21 with antenna mounted near the rudder
> > pedals and I have not heard him complain of problems with his MRX.
>
> > If in doubt send it back for calibration *Mine had degraded to the
> > point it was useless and ZAON fixed it for me at no charge.
>
> > Andy
>
> Folks, the MRX often displays wrong code and occasionally wrong
> altitude. This is a common issue with this unit and nothing can be be
> done about it. I recalibrated the threshold and returned my unit twice
> complaining about it until they admitted this is normal due to design
> limitations. The code and altitude usually gets messed up when flying
> close to another glider and may stay wrong for sometime after that.
> Just ignore the code. As for the altitude error assume a 500 feet
> error so always search above and below you when it shows less than 500
> feet difference.
> My above comments are based on 5 years using this unit, multiple
> correspondents with the factory and other pilots experience.
>
> Ramy

Its true that the MRX or any of these PCAS units when handling Mode C
may get confused. For example they just cannot absolutely cannot tell
apart what may be altitude or squawk code replies and clearly use some
smarts to guess/manage this. That they really work as well as they do
is very impressive.

While folks like Ramy and Andy know what is going on I still see
pilots confused about this local transponder thing. One (obvious)
problem is if you are messing around with this on the ground your
local transponder may not be being interrogated and the PCAS may think
some nearby transponder is the local one. Read the manual carefully
and know how to determine if the Zaon is seeing you local transponder
and using its altitude or not.

If the Zaon is not using the local transponder and instead usign its
pressure sensor than cockpit ambient pressure may cause altitude
differences that it reports threats at.

Transponder antennas mounted near the PCAS unit (especially when not
shielded by a ground plane) are problematic since they just provide
way too much power to the PCAS receiver and can cause misreadings like
that described.

If having problems with the Zaon local transponder I would still try
to work through all things, transponder antenna location, adjusting
the Zaon like Andy mentioned. etc. and see what is possible. I have my
MRX sitting on top of my glareshield and the transponder antenna
installed in the factory location in my ASH-26E and all operates very
reliably (with the MRX using the local transponder).

Darryl