I'm posting this here as the issue is electric related. And hoping someone can give me some advice on where to start looking.
I've got an ORRA authorisation, and have a Kenwood TK7160 in my Patrol. Fantastic radio. The 1/4 wave antenna is installed above the right wheel arch. The radio has been installed for a year or two now, and I've had no issues with it at all until relatively recently.
When the ignition is on on the vehicle (both when the motor is started and when it is off), I have started picking up interference on ORRA8 (steady static hiss). There is also interference on all channels using the same frequency as ORRA8 (ORRA1, and I *think* ORRA5). However, since the other two channels are toned, the radio does not make the general static noise. Well, generally wont, but something will generate the correct tone for ORRA1 when I hit about 2500 revs. Then I will get a burst of static, followed by silence again as I pass 2500 revs.
I've got no idea what is causing this. I have checked the following:
1: There are no breaks or issues with the antenna cables or radio power cables.
2: Radio power comes directly from the battery (properly fused on the battery side).
3: There is undefined ohm reading (ie: no connectivity whatsoever) between antenna centre and antenna outer cores.
4: There is zero ohm reading (ie: good connectivity) between radio-side centre core on antenna cable and the whip of the antenna.
5: There is zero ohm reading (ie: good connectivity) between radio-side outer core on antenna cable and the antenna base.
6: Likewise, there is zero ohm reading (ie: good connectivity) between radio-side outer core on antenna cable and Earth.
In other words, all seems to be perfect. But the problems persist.
The radio seems to be working well when there is no interference (ie: when ignition is off and similar), but I wonder about my range occasionally. On a few trips, it has seemed to be particularly short. On other occasions, it has seemed to be perfect. I regularly pick up radio traffic in Pretoria and Midrand from the R511 (depending on where I am, as the geography is a little weird there, and VHF is affected by line of sight).
In short: I believe there is some electric bit that is causing interference with the radio. This would be something which is on whenever the vehicle's ignition is in the on position (even though the motor is not running). This is something which is presumably affected by engine revolutions or alternator voltage (hence the correct "tones" being generated) when I hit 2500 revs.
I've checked the harness all over the place for breaks or shorts, but there is absolutely nothing. All looks perfect.
Oh - a final note: When the radio is picking up interference, and I open the driver side window about 5cm's, the interference stops. There is also no interference when I operate the driver's side window. This could indicate that the issue is voltage related, except that this is only when I operate the driver's side window. It's all very strange, and I cannot work out what is going on. It may be that the radio set is damaged in some way, but trying to work out cheaper.
In short: Anybody with any ideas on where to start, please let me know. Appreciate it.