Trouble With Interference

[DieselSlug]

Recently bought a Cobra NW 29LTD CB. I just installed them into my truck running the power directly off the positive battery, and the ground directly to the negative side of the battery. I have been getting interference with something else in my truck, only when the key is in the run position. There is no interference while it is in the acc. position. I have a wilson 2000 trucker antenna mounted behind the cab on the drivers side front bed rail. The truck is a 1994 Silverado 6.5 TD with an electronic DS4 injection system. I have many add ons in the truck, like a 10-disc cd changer run with an FM transmitter to 89.1, and a XM radio with a transmitter tuned to 88.7. I went out and bought a few choke sleeve's and tried tesing it on various lines, i found one interference was the xm transmitter, so one was eliminated with a sleeve. However i am still getting a super sparratic squeal. Not constant at all like you would think with a power source. With the key in the run position it sometimes does it and other times it doesnt. The antenna is good, i tried a freinds k40 and his did the same thing. Any insight would be greatly appreciated. I have also done this at my house and in many parking lots away from powerlines and things like that. Still does it everywhere. I have gotten my SWR down to a little below 2, i think the antenna needs a small amount of trimming. SHould i buy a noise filter for the power supply? Would this help me?

 

[dms4x4]

When you say the problem is present with the key in the "run" position, does that mean with the engine running? If the source is a conductive emmission, I'm guessing there will be as much noise on the battery as any where else. With the engine running, or what ever condition creates the interference, try pulling fuses one at a time. If you can isolate where it's coming from, that will go a long ways toward fixing it.

One item that connects directly to the battery is the alternator. Keep in mind the alternator creates an alternating current, then with switching diodes, clips the AC and makes DC. When things turn on and off it creates noise. I'm sure there is some signal conditioning and filtering circuits in the alternator, but maybe it's not as good as it needs to be.

 

[tommystunes]

I tend to agree with dms. Try grounding to the floor pan (scrape paint first).There are also rumors the optical sensor filter harness that may or may not still be present was originally designed as noise suppression for the radio.
More detailed info,such as if the noise varies with rpm,changes with headlights,etc...

 

[DieselSlug]

I have narrowed the source down of the main interference. It is the Pyro gauge. When the pyro gauge is on i get a squeeling sound, that is super sparratic... So for now i put the pyro on a switch.

 

[dms4x4]

Hmmm......... I'm ignorant. What exactly is a pyro guage, and what type of sensor does it use?

 

[DEERE3594]

Hmmm......... I'm ignorant. What exactly is a pyro guage, and what type of sensor does it use?

EGT. sensor is in exhaust crossover or down pipe :thumbsup:

 

[dms4x4]

EGT. sensor is in exhaust crossover or down pipe :thumbsup:

So it's essentially a thermocouple? That would be the last thing I would expect to cause interference in a radio or anything else.

 

[DieselSlug]

This is a Optix pyro gauge, and one benefit to it is that the thermo couple is NOT in the probe, it is in the gauge part. So it is on my dash next to all my electronics. SO for now it is just on a switch....

 

[WarWagon]

Put that device on the choke...

 

[DieselSlug]

I have put a choke on each and all the wires coming out of the pyro, nothing works, must be too much of a signal coming from inside the unit itself....