Funke ATR833 VHF incoming noise issue

[gammaxy]

Hi again. Seems like Wolle and I have the same issue. But what can be done with the signal/noise ratio? At our airfield we have 3 Sonex aircraft, and I am the only one with this problem. The only thing different with my fuselage is that it has been coated on the inside of the aluminium. Thinking the contunuity in the metal is disrupted. Reading thru countless forums, I stumbeled upon static buildup. Could it be possible that I need bonding on fuselage and wings? I read that there should be a minimal amount of resistance thru all metal components. Will try to do some measurements from main ground to wings and tail.

I think bonding is unrelated to your problem. What matters is that the antenna coax has a good, clean connection to the fuselage skin near the antenna. On my antenna, this is provided through some toothed locking washers. You could probably check this with a multimeter by disconnecting the coax from the antenna (to remove the cable and radio from the measurement) and measure the resistance between the outer conductor and the fuselage skin nearby. An SWR meter would likely be even better, because you could test the whole cable from the radio through the antenna. There's some inexpensive VNAs available these days like the NanoVNA that could make this measurement: https://www.amazon.com/NanoVNA-H4-Analyzer-10KHz-1-5GHz-Measuring-Parameters/dp/B085CFHTBM

I suspect this isn't your problem, though, since you transmit and receive at high quality.

Do you hear the noise in the background during the transmission also? Is it comparable in loudness to the transmission? If it is, then I suspect the problem is on your end and you either need to focus on the antenna installation or noise. Does it get louder when the transmission ends? Does the noise change depending on which ignition you're using or engine RPM? Or whether the alternator is charging the battery? Have you contacted FUNKE about it? To me, it sounds like something one of their engineers could diagnose better since they would understand their squelch logic.

[Janex]

I did a resistance check of the whole airplane with a Fluke 1653B instrument. Checked all surfaces, and got very low reisistance (0.00 Ohm). Checked the trim wire aswell, and this was higher resistance. Will ground this properly.
I am the only one with FUNKE 833 radio installed. This is my second ATR833 radio. Funke sent me a new MKII, when nothing helped with the first version. It got better, but still a little bit noise. It is only when I'm in the air I get noise. On the ground it works fine.
All cables and wires have been changed/upgraded. Using RG400 for antenna. Have ensured that antenna connection is good. Antenna is the only thing I have not changed.
There is a "burp" when receiving transmissions. Funke has no clue what is going on.