Radio interference

[10ixwwybk2]

Please can someone help.
My RV9A is equipped with twin Skyview, integrated Transponder, autopilot and EMS.
In the two years since the first flight I have had a radio interference problem.
I get a 'beep beep beep' over the radio, mainly when taxying or at lower rpm. The frequency of the 'beep' ranges from 2 or 3 per second at low rpm to very fast as you accelerate, in fact I think in normal flight it is probably so fast in merges into a contin ous background noise that is not so noticeable but becomes apparent when slowing down in the circuit.
When the alternator is turned off it disappears, so my fault finding was focused on the alternator and grounding issues.
So I have covered things like, the separating wiring that might give interference, only grounding one end of the mag wire shield, I also tried a choke /condenser across the main power supply.
I have now isolated the Audio inputs to the radio, a Funke ATR 833, when the Dynon audio input was disconnected the noise disappeared. I re-read the installation manual and found I should only connect the audio output of one of the Dynons and I should ground from the frame of the radio to the frame of the Skyview. I did both of these, but no improvement.
I am sorry this is a bit protracted, but having talked to a lot of people and searched on line, I don't know what to try next.
One last thought, the ground from the radio goes to the Skyview that I disconnected not the connected one. It is my only last option but I doubt that is it.
Robin

 

[Dynon]

So one clarification first: You should have BOTH displays' audio outputs connected to your audio device. What kind of audio panel / intercom is your SkyView audio output connected to? Is it a dedicated input? Mono or Stereo?

 

[Dynon]

A few other tests that might help shed light on what's going on here:

1) Disconnect backup battery from SkyView. Does it go away?
2) Does the volume control in SkyView have anything to do with it?
3) Is this a plastic panel?
4) Is the SkyView super well grounded to the radio/intercom?
5) Turn the AOA audio off in the Audio Setup menu. Does that change anything?

 

[10ixwwybk2]

Thank you for responding.
To answer reply 1.
I misread the installation manual when I disconnected the audio output of one of the Skyviews, but the fault was there prior to that.
I do not have an audio panel, the Funke ATR833 has an integral intercom.
It is a mono input to the radio that is shared with the stall warner and an audio jack that is not used. The left and right audio outputs from both Skyviews are commoned.
Reply 2.
I will check your suggestions in the plane.
It is an aluminum panel.
Everything in the plane goes to common ground and last week ran a 16g wire from the radio frame to the Skyview frame, but only to one of the Skyviews.
Thanks,
Robin

 

[ploucandco]

I don't want to be negative on a radio that is being produced by an otherwise producer of excellent avionics equipment, but the Funke ATR833 is extremely sensitive in terms of parasitics (EMC issues). A friend of mine just upgraded his panel containing an ATR600 with an ATR833. He had to replace his ipad and phone 12V adapters due to EMC issues. When on the ATR600 there were no issues at all.

 

[RVDan]

Also, if you are paralleling audio inputs from multiple devices without isolation, you can get unexpected results as the systems will load each others output. Not good practice in general.

 

[10ixwwybk2]

I checked out the suggestions on the plane today.
Disconnecting the standby battery, turning down the volume of Skyview and turning off the AOA had no affect to the interference.
Disconnecting the Dynon audio output removed the interference all together.
Switching off either of the Dynon Skyviews had no effect and significantly with both Dynons switched off and the audio connected there was still interference.
Switching off the alternator removes the interference, but I have checked all grounding to do with the alternator or mags.
I have also now grounded the frames of both Dynons to the ATR 833 radio.
I am also looking to install a TRX 1500 traffic sensor, will commoning all these audio inputs into the radio, there is also the stall Warner, have a compatibility issue.
Robin