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