Radio transmission gremlin

I am trying to finish my IV with a 582 and am getting a crackling sound during transmission at 4000 or more RPMs. No noise at lower RPM’s and if the engine is off. The radio is a used Val Com 760 TSO that came with the multiple boxes of parts when I bought the project. I tested the antenna and coax while engine is running using a handheld instead of my ratio and no issues. Last month I had a friend add some ferrites to the wires because prior to adding them the transmission was full of static and unrecognizable. The ferrites remove 98% of the static noise. At the suggestion of another forum member, we wired a .05 capacitor from the power wire to the ground wire that feeds the radio to remove the crackling sound at the higher RPM’s with no improvement. Any suggestions on getting rid of the crackling noise at higher RPM’s?

Thanks

Have you checked for ground loops? ie: multiple ground paths to the radio? Are the ring portions of your headset and microphone jacks grounded to the airframe and feeding back to the radio? Do your radio and intercom ground to the same point? Are you using a common ground location?

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Originally Posted by 109JB

Have you checked for ground loops? ie: multiple ground paths to the radio? Are the ring portions of your headset and microphone jacks grounded to the airframe and feeding back to the radio? Do your radio and intercom ground to the same point? Are you using a common ground location?

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I did check for ground loops and had a friend who is much more knowledgeable than I when it comes to electronics along with an A&P and we can’t find an answer.

Another possibility: Do all your spark plugs have solid tips where the ignition wire connects? In the past I had mistakenly put plugs in my Rotax 503 (on my Quad City Challenger) with screw on tips and over time the tips came loose and started to arc inside at the threaded interface. This caused terrible static noise on the intercom.

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Originally Posted by Birdseyeview

Another possibility: Do all your spark plugs have solid tips where the ignition wire connects? In the past I had mistakenly put plugs in my Rotax 503 (on my Quad City Challenger) with screw on tips and over time the tips came loose and started to arc inside at the threaded interface. This caused terrible static noise on the intercom.

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The plugs with the solid tips have 2 hours on them and I replaced the spark plug boots.

Try grounding the radio box itself back to your common ground.....not just the tray. Make sure all ground wire associated with that radio is also brought back to that common ground.

What coax are you using? If RG-58 try ordering RG-400 from Aircraft Spruce that is cut to and terminated to the length of your existing cables.
https://www.aircraftspruce.com/catal...s/11-09202.php
I had a lot of radio noise problems with RG-58 and all of it disappeared with the more expensive RG-400. I thew the kitchen sink at the problems too; ferrites, filter capacitor, checked all my grounds. Keep those but consider the RG-400 cable.

I also added another ground plane sheet underneath my main antenna mounted to the boss behind the turtle deck but underneath the fabric covering. It's attached to the antenna's coax grounded base connection. John McBean stated that it would increase my radio's range....and it DID.

BobRS
Kitfox SS7, Rotax 914
Albuquerque, NM