jcarlyle wrote:

On Mar 24, 6:06 pm, Darryl Ramm wrote:
On Mar 24, 3:33 pm, Eric Greenwell wrote:

jcarlyle wrote:
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.
Does his glider have a transponder in it?
Do you know that the towplane encoder was working correctly?
Lets play 20 questions... :-)

Since the temperature was cold. Was this the first tow of the day? Any
chance the transponder had just been turned on within a few minutes
earlier and was still warming up?
Eric, the club G103 we were in does not have a transpondert. The
towplane encoder is working properly according to ATC.

OK, then the MRX should be using it's internal altimeter, as Darryl
thought. If the encoder altitude output is a just a little erratic,
you'd be able to notice while ATC might not. They would not be able to
tell the difference between an unsteady climb and a slightly erratic
encoder, I'm guessing.

Darryl, it wasn't the first tow of the day, so yes, the encoder was
warmed up. Let's ask the other 17 questions after I fly my transponder
equipped glider with him and his MRX in his non-transponder equipped
glider.

Or, you could fly with the MRX in your glider, which would make the MRX
use your encoder altitude instead of it's internal altimeter. That might
tell you if the problem is the internal altimeter.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* Sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org