OK, so heres the deal, I have a 2 way mobile radio for thee volunteer fir department i am on. wheen i wire it up, (good power supply, good ground) and key in the accessory or off position, it works GREAT. but when i turn the key on, i get all sorts of interference until i unhook the attenna, then no interference what so ever. DOES ANYONE HAVE ANY IDEA WHY IT WOULD BE DOING THIS? If it is any help, we just switched to narrow band radio frequency today.

 

I usually install a noise filter in line with the power to remove ignition interference. You can pick one up at Radio Shack for like $9? It'll quiet it down quite a bit.

 

i finally tracked down the problem. The HID headlights are somehow backfeeding the power system and causing the interference

 

The filter right behind the radio would still help alleviate the noise.

 

Is your antenna wire ran close to the headlight wires? If so try to run it else where. You can also use some metal jacket or tin foil to use as more insulation.

 

i am going to try the noise filter tomorrow, but the antenna wire is no where close to the headlight wires. I have tried 3 different antennas with the same result. If the noise filter does not work, then i am going to put my headlights back to the stock bulbs. I can do without those.

 

Very good idea!
Just add a ground cable to the shielding, otherwise it is useless.
The ground cable is grounded only in a single point- not on both ends-otherwise you create another loop.
Make sure all your additional connections(return and live wires!) go directly to the battery. Do not interfere somewhere in the truck harness. This causes interference in most cases to ground or live loops.

Filters are wasted money, if you know the ropes how to avoid noise.

 

Try turning your wipers on while the radio is on...You'll probably hear those too.

 

You know the reason for that noise?
Lack of proper grounding-again...

 

I removed the radio from the truck, had it sitting on the firewall, hooked up. wires not close to any other wiring on the truck. turn the key to on, headlights automatically come on, static starts. i manually turn off the headlights, and the static stops.