Whistling receive

This whistling in the receive, does it change pitch with the RPM of the engine? It sounds like alternator whine.

You can filter out the AC ripple on the DC power feed with a choke, but if there is a bad diode in the alternator, it won't cure it completely.

 

It also could be where your power hookups are. try another source with both + and -

 

It is possible to do so, but it is also possible you might not notice a difference if the noise is coming from something in your truck.

 

Run a separate ground from the case of your radio to a solid ground on the truck. I've seen this work before. You might check the ground on your QualComm if you have one, they can generate all kinds of noise in anything audio.

 

OK ... I am posting this by going around the barn instead of through it.

we have established a few things.

1 - that you have a crap load of things that can cause the issue on the power "grid" like qualcomm and gps unit. CMS unit ?

2 - you unhook the antenna, it stops.

3 - you have it hooked up to the crap power source - aka cb posts.

So a little explanation and story.

first off the ultrasonics produced by something that is what causes this type of interference happens often but it is not normally generated in the truck by the truck itself.

let's take one example - the gps unit.

The 12 volt plug in power supply for many gps units is a cheap switching unit which in itself causes these ultrasonics to be produced and they are very dirty despite the fact that there is a law against them producing anything. This is spread into the truck and what is called harmonics is also produced by these units.

real world example is I had issues with my CB in my truck for a long time, buzzing coming from it. I put a 15 amp inline filter (not a cheap one but a really good one), had the radio aligned and so on. I accidentally tripped over the problem when I was going into the sleeper and the wire got caught on my foot and yanked the power supply out of the plug, no more noise. So I never thought of it at that time this was the real cause of it, so later on I built a good linear power supply for the GPS unit but it wasn't the real culprit where the noise was coming into the radio - I will get to that now.

One thing that I also did was to replace the coax. I had on that truck a multiplex antenna system that worked OK, not super but OK. Once I replaced that, the noise vanished.

So here is what i see, you went through the basics, there are only two ways this noise gets into the radio, through the power and through the coax, I would venture to say your next step is to replace the coax and make sure it has a common current choke on it because the coax is both leaky and acting like an antenna, which is can't do.