No idea, but I had the noise all the way up to and back from the Rubicon so not a local transmitter.
Actually not 'all the way'. Sometimes it would stop for a while but it always came back.
I do have a number of high powered comercial transmitters a few miles away; TV and microwave, not sure what else. But I don't really think they have anything to do with it.
I would put a reflected power meter into the antenna line to at least see what the radio thinks it has for an antenna. The crazy thing is, very few people ever tune their antennas or ensure adequate grounding. "It works" so they think that is good. People put 75 Watt transmitters onto antennas that aren't going to radiate more than a fraction of the power. If you try that on the 10M band, or the 20M or 40M with an older radio, you'll burn up the output transistors within minutes. Modern radios with FET output stages "fold back" when they get hot, so prevent serious damage to themselves.
If the interference is 'local' to the truck, I'd say it can only be a capacitive grounding issue due to the sporadic nature of the noise. Does it change with engine on to engine off?
I just listened to your recording again, and the fact that it stops on certain frequencies infers that it is external interference which 'beats' with one of the oscillator frequencies. I'm not sure that you can cure this. The front end of the radio might just be too sensitive for whatever that interference is. Is there a "distant/local" setting on the radio? That might de-sense the receiver and would at least isolate that potential problem.
Edited by GraemeWare, 25 June 2017 - 09:11 AM.
Graeme Ware -- San Carlos, CA
1990 Range Rover Classic - LT230 Transfer box, Warn winch, 2" lift, 235/85-16 Dunlop MUD Rovers, "Blue Submarine"
1996 Discovery 1 (R380 Manual Transmission, Ashcroft under-drive, RoverWare rear bumper, 33x12.5-15 BFG ATs) -- we call her "Katrina" -- Fordyce 7.5 mile survivor
1999 Discovery 2 (D1 CDL Linkage, 265/75-16 BFG A/T KO, RoverWare front and rear bumper)
1993 Jaguar XJS convertible; 1971 Triumph GT6; 1959 Morris Minor convertible
other assorted British pot metal ...