Mode-C Problem (AK-350)

Guys,

I got a report form 2 different ATC facilities yesterday that my mode-c return was indication 1000 feet higher than I actually was (one report was actually 1200' higher). I'm using a AK-350 encoder. Does anyone have any troubleshooting suggestions short of taking it to an avionics shop or just replacing the encoder.

It seems I've heard that the AK-350 can be kind of problematic and unreliable.

Thanks,
David Clay

One thing to check

Have you checked the wiring between the encoder and transponder? The transponders use gray code encoding and having two wires swapped would give you a bad reading. Kit Planes had a do it yourself led readout for checking what was coming out of the encoder. I don't remember what issue but I thing it is still also found on RST Engineerings articles page. Hope this helps.

Paul
pczar3
N694BP reserved

Ameriking AK-350 trouble...

I have had the very same problem with this encoder.. I then brought it to the shop, where they ran it up without a problem and hey presto it worked fine for another few months.

Then in 100 degree weather in Las Vegas during the summer, I took off after having it on the ground overnight to be told that I was reading 600ft lower than I was. I thought it was the heat etc., but after research, it seemed not to be..

So what was it. It turned out to be the 'time it takes for the encoder to heat up'. Bottom line: Leave the transponder on standby for at least 10 minutes (while your oil is warming), and you are not likely to have a problem. If you don't give it lots of time to heat up in 'standby mode', you are much more likely to get errors.

Thats not to say that this is acceptable in any way, but I have not had any problems in 6 mths since I started doing this. If it ever does finally pack it in, I will just buy a different brand.

I hope this helps.

Encoder Warm-up Time

hughfi,

Thanks for the info. I always let is warm up in stand-by mode but I'm not sure if I've ever given it at least 10 minutes. I'll give that a try the next time I fly. If this doesn't help I think I'm just going to replace it.

Thanks,
David Clay