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My little ICS+ Nav/Com/Glideslope/Localizer seems to be
very sensitive to avionics-generated RFI; I have to have the squelch at max to
keep out hiss! I'm not sure how it's getting into the receiver, but I think it
may be as antenna currents on the coax which are picked up near the
receiver and then go out and enter the VOR and GS antennas mounted in
the inner wings. The other day I was doing some signal sniffing with my ICOM
A4 and its rubber-ducky, and I found I needed the A4 squelch set all
the way up to 7 (of 9) to get rid of the hiss. I turned off my Dynon and still
got hiss from my TruTrak Pictorial Pilot. I turned it off and got hiss from my
Dynon when on. Originally, the Dynon was really bad until I installed the $10
filter-dongle I obtained from Dynon and installed it on the input
connector. That A4 is really great for signal sniffing, since you can scan the
whole Comm band in small steps and keep playing with the squelch to seek out the
various interference frequencies. These avionics units with their digital
divider circuits put out lots of harmonics. That's why you may get interference
on one frequency but not on another. Surprisingly, the little Radio Shack 14V-6V
1A buck-converter I installed in back of the instrument panel to power my Delphi
XM receiver was quiet!
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