NARCO AT 150 Putting out two Codes?

[Gone]

Today, while flying home from Waterloo, ON to Rockcliffe, Toronto Centre informed me that my transponder was putting out two separate signals - the code they gave and one that was up by four on the last digit.  My own ADSB in (Foreflight/UAvionix Sentry) also warned me that an aircraft was within 25 feet of me at the same altitude.  

I know it is an old tech device, but I am not yet ready to shell out $5000 for a full ADSB-in/out head to put in the panel.  I have a Tail Beacon to meet the US ADSB out mandate and that works fine.  Before anyone asks, I checked with the controllers after cutting the power to the Tail Beacon and the problem continued anyway.

Cheapest solution is probably to get my old Narco repaired and have the antennae all checked - but I thought I would ask.  Any ideas on what to look for? 

[carusoam]

See if @Alan Fox has a clue of what is going on….

he might also have an updated technology…

Best regards,

-a-

[N201MKTurbo]

The selector switch on your transponder is probably dirty and intermittent. It would be the one on the right. Each switch has three binary code lines. If the MSB line was intermittently making connection, it would alternately put out the correct code and the code either 4 higher or 4 lower depending on how it is wired.

Your best bet if this happens is to spin the knob around. 

[EricJ]

I don't know how the AT 150 is implemented, particularly the knobs, but adding four to the last digit is a bit toggling between 1 and 0 in the last digit.   That may be a connection in the knob or it may be something else internal in the interface.

Wiggling the knob for the last digit might help.   Spraying some contact cleaner around the internals for the last knob might help, too.

Edit:  I see Rich beat me by a few minutes. 

[carusoam]

Way to go Rich!

MS has soooo much knowledge!

And Rich Is a huge part of it….

Best regards,

-a-

[Gone]

Thanks guys. I will take that knob for a dance, spin it around a couple times, enter our local Class E space in Gatineau for a few circuits and see if it has resolved itself.  

 I will let you know how it went. 

[Browncbr1]

@Ned Gravel  I’ve got one on the shelf that worked just fine when removed for upgrade.  I also have a nearly new Sandia digital encoder that can go with it.  Let me know by PM if needed.  Craig

[chriscalandro]

I have one for 200$

[Gone]

@Browncbr1 and @chriscalandro:

thanks guys for the offers.   Spun the knobs. Flew the test fight. All good.