i just insalled a cobra cb in my truck, when the engine is off there is no problem. when i turn the key to run and the fuel pump comes on i get a little bit of static. when i start the engine the signal meter goes almost to full. there isnt any change in the tone with the change in the engine RPM, i tried a few diffrent grounds with no change. i also have an Alinco amiture radio hooked up with no problem. any ideas? i have the power running input on the back of the fuze box.

 

where are you running he cable? through the firewall? more than likely it's close to another wire which is why it's cauing that sound.

you could also adjust your squelch and some cobras have noise block features.

 

That's your first problem. You get a lot of RF interference through the hot lead, especially running it off the fuse box. Your best bet is to run the hot lead (the + wire) directly to the + terminal on your battery. I'd suggest grounding the CB somewhere in the engine bay as well. That'll get rid of a lot of your static, but not all. The Ranger fuel pumps are terrible when it comes to interference.
Hope that helps!

 

Ford's have had a problem (there is a TSB for some models) with electrical noise from the fuel pump.

It can come in two different ways. From the power/ground wiring, or via the antenna.

Your Alinco, I presume, is an FM rig -- you will have not problems with FM typically because the modulation system itself is inherently noise immune. Also, the intensity of radiated noise from most arc type noises drops steadily with frequency and if your Alinco is a 2 meter rig, it's at 5 times or so the frequency of the CB.

So, we're back to seeing where it comes from. For starters, do you ever listen to AM radio? Put you factory radio to use and tune in a weak AM station and see what you get.

Ground loops are a killer. Sometimes not grounding the antenna at the base of it increases noise sensitivity since the effective signal reference path from the base of the antenna is through the vehicle body which carries all the return currents from the electrical systems. This can be disastrous. If your antenna feed line is not grounded at the base of the antenna, do that and see if it helps. By having the ground reference return through the coax shield, you may reduce noise.

Now here's the funny part: sometimes grounding the feedline at the base of the antenna INCREASES noise (though not usually). The occurs only when there is such a crappy ground path back to the battery from the fuel pump, say, that the fuel pump uses the coax shield as a ground path for it's motor current to some extent! The solution here is to rework and restore any damaged or missing ground straps. There are a couple under the truck between the frame and the body and you should inspect them.

Just some things off the top of my head to think about.

I always run a separate ground right from the battery to any critical radios, or radios with noise problems.

 

thanks for the help, ill try a few of those things. i think it is mostly from the fuel pump. ill try grounding straight to the batt and see what happens. ihave the ant mounted to the truck box, so ill try to improve its ground as well.

 

I have the same issue very frustrating, I earthed to the battery and still very noisy when running. Would be good if someone has a fix for this.