Intercom Static - Increases with RPM's

[Tyler Beevers]

Happy Thanksgiving! New owner of a '65 Cherokee 235 with a Sigtonic SPO-4S installed. I’ve got an issue I’m dealing with so thought I’d post just to see if you’ve heard something similar. I flew a couple days ago and everything was fine. Pulled it out of the hangar yesterday and intercom audio before engine started was clear. Cranked engine and noticed an intermittent, static click but nothing alarming. When I did the run up, the static became unbearable so had to take it back to the hangar. Tower could hear me fine with no static at all so purely related to intercom. Different mag’s didn’t change it, turned off alternator and didn’t change it. My wife pulled out the USB socket charger thing and it stopped for a few seconds and it eventually started again but didn't seem to be quite as bad...not sure if that was coincidence or not? Ground wire under cowling is tight. With engine off, there are no issues at all.

Not sure if the vibration from the engine is causing this or if it’s interference from something else? I didn't pull fuses so thinking about doing that today to check different circuits. Completely stumped so thought I’d ask to see if you’ve heard of this before?

Thanks in advance!

 

[bflynn]

I wouldn't think vibration so much as electronic interference, most commonly the ignition system or alternator. Check the wiring for these in the engine compartment and see if you can find any source that appears to have compromised wiring. Vibrations can weaken the wiring.

It's geared toward builders, but EAA has a good checklist of things to look at: https://www.eaa.org/eaa/aircraft-bu...ruments-and-avionics/why-tolerate-radio-noise

 

[Tyler Beevers]

I wouldn't think vibration so much as electronic interference, most commonly the ignition system or alternator. Check the wiring for these in the engine compartment and see if you can find any source that appears to have compromised wiring. Vibrations can weaken the wiring.

It's geared toward builders, but EAA has a good checklist of things to look at: https://www.eaa.org/eaa/aircraft-bu...ruments-and-avionics/why-tolerate-radio-noise

Ok, good to know! I'll take a closer look this afternoon!

 

[Doug Reid]

If you have access to a handheld, see if you hear the interference on it as well.
If you have ignition noise, you should hear the " pecking " sound on the handheld.