Problems.. MGL V- 16 and N- 16 controlled and utilized in a razor head.

[Spitfiremk26]

MGL V- 16 and N- 16 controlled and utilized in a razor head.

We are having a very difficult time chasing down this gremlin/s we have spoken to A&P’s and avionics people and have not been able to find any resolution to the following. This system was prewired on the bench at avionics company a 1,000 miles away. We can not rip it out of the plane and do not have a reliable radio to fly it cross country to get it reviewed... We understand we have a ground loop, but several people have reviewed and checked it. we are all scratching our heads....

We also would like any recommendations on its resolution plus any filters that we might be able to add to the system to remove these problems and complications. That said....

I’m having feedback of my radios in transmissions to other radios and also that same feedback static noises on my audio headphones. This is found in different configurations which I will explain below.
With the engine off and no battery charger the radios have the following issues in the specific configuration identified below.
(Also note that there is an additional feedback picked up from the electronic ignition/magneto win that is running. The system has 1 manual magneto coil and the additional magneto coil is an electronic type system. When electronic magneto is in the off position and the engine is running on the manual magneto the interference noise from that system goes away completely. Yet, the Garmin GNX 375 GPS-Transponder ADS-B in/out still produces its background noise and interference in the headphones, additionally it is also picked up during COM2 to COM1 transmission. With COM1 MGL V-16 used alone and other systems shut off communications are relatively clear and optimal.)
My avionics array consists of:
MGL V- 16 and N- 16 controlled and utilized in a razor head.
V-16 is using a Redfin dorsal antenna
N – 16 is utilizing a V whisker antenna belly mounted in the tail
settings for the MGL V 16
squelch is at 96- 97%
intercom IC 27%

PMA 4000 radio switch panel
Garmin GNX 375 GPS-Transponder ADS-B in/out with Shark fin antenna
GTR -200 Garmin using a belly mounted at Redfin antenna
PMA 4000 radio switch panel switched to COM 1 without Garmin GNX 375 GPS activated/off and GTR -200 Garmin also off. COM1 is relatively clear with a very minor home in the background. When I press the Nav 1 activation button I get an increase of that background hum heard on the MGL V- 16
when I turn on the GTR -200 Garmin with the radio panel switched to COM1 I get a high pitched “eeeeee” when I switch to COM 2 it’s relatively quiet. But, when I turn off the on off button for the squelch I get a very loud buzzing like a wire is frying sound With popping noise. When I turn the squelch back on when on COM2 of the GTR 200 the goes clear.
When I switched to COM1 and turn on the Garmin GNX 375 GPS-Transponder ADS-B in/out I get a fairly loud “eeeeee” with some popping noise. When I go to COM2 with the 375 and GTR 200 it goes quiet. When I turn off the PMA 4000 switch panel I still get the interference noise from the GPS.
Transmitting COM2 to COM1 I have, a audio playback feature on the MGL V-16. When I play back the transmission, listening on COM1 the recording picks up the buzzing sound “eeeee” in the recorded transmission audio.

COM 1 and when I turn off the Garmin GNX 375 GPS-Transponder ADS-B in/out the noise goes away.
Then when I go to com1 with the Garmin GNX 375 GPS-Transponder ADS-B in/out turned off it is mostly clear, with a slight minor buzz interference with the GTR -200 Garmin radio on . While monitoring COM1 When I shut off the COM2 GTR -200 Garmin radio COM1 is completely clear.

One another thing that I have noted, is that when I am transmitting GTR -200 Garmin radio COM2 to MGL V-16 COM1 I noticed on the MGL razor radio panel indicator that the VOR indicator to and from bounces back and forth with the little airplane icon from left to right. The N – 16 NAV 1 is utilizing a V whisker antenna belly mounted in the tail 20 feet away from GTR -200 Garmin using a belly mounted at Redfin antenna. We cannot mount the whisker antenna anywhere else nor the redfin COM2 antenna also on the belly. Were not quite sure what type of interference that this is going to cause an impact during and in approach, and is this only a momentary event that we should not be concerned with?

[rainier]

Well, judging by what you write - it appears to be multiple issues.
It's not going to be possible to solve this with a few posts - you will need to find somebody that knows how to wire up audio systems in an aircraft.
It seems there are multiple issues - incorrect or missing cable shields, ground loop, incorrect audio signal ground points used etc.
Squeeling on TX is almost always caused by the transmitted RF leaking back into your microphone inputs - in this case likely your audio panel.
Very common also that you have sidetone from the radio coupling back into the microphone input - that also closes the audio feedback loop.

I'd love to be able to point out exactly where the issues are - but unfortunately that is not possible. Sometimes the only way to fix multiple issues like this is to rip everything out - have a good look at what the intercom installation manual tells you to do and start over.

If a very powerful COM aerial is relatively close to a NAV receiver antenna it is possible for some energy to make it to the NAV receiver. While signals from the COM radio at NAV frequencies must be at least 60db down in level (for a certified radio) and usually its much less than that - it is still fairly significant with respect to a weak VOR station. The N16 is an unusually sensitive receiver so if it finds a signal at your tuned frequency it will try and resolve it - so you may see the aircraft popping up to tell you there is a signal but it will be flagged as there is no usable modulation.

[Spitfiremk26]

Sorry for the delay we have been home sick with this flu thing....


WE will test and track your recommendations and I will be able to contact you with the results on the 17 Nov. We only work on the week ends with this during the winter.

Thank you Sir!