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Tranponder Tecnical Question.

Xkuzme1

Well Known Member
Technical question here.

My transponder went out last week. It was a KT76A. I bought a used KT76C direct replacement off of eBay.

Today the readout on the new transponder never displayed a pressure altitude.

I talked with KC approach on the way back and the were only receiving my position... no altitude.

Q: could that be my encoder?

I guess I don?t really understand the relationship between the encoder and the transponder.

Thoughts?

Thanks,

T
 
The encoder supplies the transponder with altitude data. The transponder then reports that to ATC along with the squawk code.

King was pretty famous for making a dozen different variants of each piece of avionics. A single dash number difference can mean some substantial changes in wiring and operation. You may want to verify the exact p/n of what you had and what you have now, and then spend some quality time with the manuals.

DEM
 
There is a wire on most encoders (usually pink), that old transponders would connect to ground to tell the encoder to send altitude data. Older transponders couldn?t handle continuous altitude data. Tie that wire to ground on a new encoder and see if that fixes it.
 
In all reality, you should have had a 91.413 transponder check done with an avionics shop when you replaced it. They also would have caught that.

Jay
 
FAR 91.413 - ATC transponder tests and inspections
(a) No persons may use an ATC transponder that is specified in 91.215(a), 121.345(c), or ?135.143(c) of this chapter unless, within the preceding 24 calendar months, the ATC transponder has been tested and inspected and found to comply with appendix F of part 43 of this chapter; and

(b) Following any installation or maintenance on an ATC transponder where data correspondence error could be introduced, the integrated system has been tested, inspected, and found to comply with paragraph (c), appendix E, of part 43 of this chapter.
 
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