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SL30: Unwanted frequencies

koda2

Well Known Member
A while back my SL30 went tango uniform. Took weeks to get it repaired. Had a bad nav circuit board and a couple of other things.

The avionics shop said it was extremely remote that my installation had caused it. Nonetheless, I painstakingly went thru every pin out and connection on the SL30, the CDI it was hooked to, the intercom pin outs, the PTT, and checked the nav and com wiring and coax. No shorts, good continuity,etc.

Well I put the repaired radio back in for a test, with the engine off and only the navcom system turned on. I can now transmit and my helper can hear me on a handheld, 5 x 5. However, I am picking up every unwanted frequency in my headset. I can hear AM radio stations, CB or ham radios, a huge amount of static, the squelch doesn't work and the reception from the dialed-in frequency is poor.

I must have an antenna or wiring system problems somewhere and obviously picking up unwanted RF. How do troubleshoot this further?

Dave A.
 
My first inclination is to recommend getting the metal fillings in your teeth replaced with resin ones to see if the problem goes away🤣.

This isn’t a belated April fools is it?

Well your problem would seem like a real head scratcher. AM radio frequencies are a long way from VHF com or nav frequencies as are CB frequencies. FM band and TV is much more relevent but they are FM and not AM, like our aircraft radios.
Try to listen with the SL30 turned off and see if you hear the same noise.
 
Disconnect the SL30 from the intercom or turn it off. Still have noise and unwanted signals?

Hook up headset, antenna and a PTT switch directly to the SL30.

Try a simple homemade hangar antenna.

Power directly from a good battery.

Point is basically to eliminate or isolate the trouble causing item.

Finn
 
Finn,
Thanks for the suggestions. I have tried most of those already.
Hooked up a handheld to the ship's antenna system, and it receives loud and clear.

I have three headset jacks, per PSE's instructions, that allows the com to work without an intercom. Also, the intercom itself allows the navcom to work anyway if the intercom is off or non-functioning. I still have the problem no matter which set of jacks or headset I use, or whether intercom is on or off. Or which frequency I dial in.

I have a brand new Commant 122 mounted underneath the plane so maybe that's contributing to the problem. I don't know how to test the integrity of an antenna.

Like you suggest, I am rigging up a totally separate antenna system to see if that isolates the problem. I think I can remove the nav antenna side and operate the radio without harming it.

Danny,
I appreciate the response but my patience is wearing thin. I had all the "metal" jerked out of my mouth when I came back from overseas. I was tasting mercury or "metal" every day and it was an attempt to alleviate the weird constellation of symptoms that a lot GIs had back then.

I have been jinking with this issue for almost two months. The first avionics shop I took the radio to, let it sit on the bench for a month without even bothering to see if it worked or not. I finally shipped it out to a place in Midland that does excellent work.

Finally, even though the world is getting smaller, this is still west Texas. Its not uncommon for good ol' boys in the air to talk to other good ol' boys on the ground and relive their last fishing trip using the unicom frequency. Or having some yahoo put his mic up to an AM radio and rebroadcast his favorite brand of mariachi for everybody to enjoy.

I am not an electronics whiz but to my thinking a tuner that's working properly would "tune out" neighboring frequencies and the like. Either that or I goofed the install in some way to create an unwanted antenna.

Dave A.
 
Been decades since I learned about transceivers, but I'm having a hard time imagining what could go wrong in a receiver that would cause it to pick up unwanted stations as well as the frequency you want.

Would be interesting to also have a handheld and see if you get the same odd signals when on same frequency. Someone messing with you and re-transmitting on the frequency you're monitoring?

Finn
 
Try a different headset, some noise canceling headphones can pick up stray signals when the wiring is not so good...
 
I’m guessing you have just 1 com? I am also assuming you are testing it away from metal hangars? I don’t know how long your a/c has been flying, but years ago there was a certain model of ELT that I can’t remember the name, that would cause the same issue you are describing. The test was to disconnect the ELT antenna and see if it went away. It’s a long shot...

Jay
 
Doesn't quite fit the symptoms, but the cheap LED ceiling lights in my hangar produce significant radio noise, breaking the squelch.

Someone already mentioned USB chargers. Think back; any kind of new electronics introduced in your environment (airplane, hanger, nearby...) since the SL30 went TU?

Most new battery chargers are now also switch-mode power supplies (likely to emit noise).

Perhaps a bit farfetched, but could imagine that such noise sources could mix with AM station signals and be rectified (demodulated) in headsets and become audible.

Finn
 
Have you called the shop that did the work?
Hopefully you are aware of what’s going on here. Some years back Garmin ‘forced’ faa licensed shops to send the sl30 back to them, where it would be fixed for one price fits all (e.g., anything from a fuse to a complete burn out, same price). The price is not cheap. If that’s what happened, send it back. It should work. More likely, you used a non-faa repair shop, which does not have the latest manuals, because Garmin won’t sell them. Since the radio worked okay in the past, now doesn’t in the same airplane, most likely there is an issue inside the sl30.
One thought: you’re not parked close to a high power TV or AM or FM or radar station, are you? That can do strange things. But since it worked before, my bet is something inside the box.
 
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