GRT Avionics

I am fighting a problem between my HX and my Becker 4401 transponder.
The Transponder show what altitude it is squawking on the display on the face.
I am sending the encoder data out of the HX by way of a cable that I made.

Problem is that whenever the HX is booted up and running the transponder is receiving 41,500 feet from the encoder. When the HX is not running it senses 61,500.

My RV doesn't go that high!!!!

I have swapped the transponder into another airplane and it works in that setting.
I have "rung out" the cable I made twice and all the pins and their locations check out.
I have swapped the two HX's that I have and they both behave this way.

Is there a setting the the Hx that needs to be set to put out the correct encoder format?

Thanks,
Duane

Duane

Are you using gray code? If so there is no gray code output on the HX and HXr systems.
I didn't look but i don't think there is a serial input for the Becker transponder.