It was 300-400 feet off, sometimes above and sometimes below us - and
we were doing a normal tow, not boxing the wake. Vents were closed (it
was 35 degrees F on the ground before takeoff). Hopefully he and I
will be able to fly together within the next month. I've got a Becker
ATC4401 that reports the encoded altitude, so we'll be able to compare
that with his MRX in real time at different separation distances and
heights.

-John

On Mar 24, 3:11 pm, Darryl Ramm wrote:
By how much? And just compared to the towplane? The altitude of the
towplane sent to the Zaon is digital. So it is unlikely to "misread"
it. It uses it's own internal altimeter to calculate the relative
altitude. I would hope they agree to 100' or so. One issue is the Zaon
pressure sensor is exposed to ambient cockpit pressure and not the
static line pressure, so opening and closing vents/speeding up etc.
might affect the relative altitude it displays. If the difference is
more than a few hundred feet I'd next suspect the pressure sensor in
the Zaon.

It may be worthwhile before sending the Zaon back to compare what the
Zaon says to another aircraft that has a transponder that shows the
encoder's pressure altitude and play with opening and closing vents.
Of course if it is just the tow plane then it's encoder may also be
faulty, or maybe it really is an RF related problem that only happens
when close to the other transponder (but unlikely).

Darryl