Alright, so I have installed a new Cobra 19 DX IV, with a 4ft Wilson antenna. Now I seem to be getting some interference that sounds like its coming from the alternator. It increases with the RPMs. I've tried grounding the antenna to different things. moving the location of the CB. Using different antennas including a Magnet mount.

Anyone have any suggestions?

 

Is your antenna mounted at least 3' from the CB?

 

Antenna is mounted on back bumper.

 

I have the same noise.. I bought a noise filter from radio shack, and on the back of the box it says to disconnect the antenna line from the cb, and if you still get the noise, install the filter. If the noise stops, then the antenna itself is picking the noise up, and you have to fix that.
You might try unhooking the antenna and go from there

 

Also, if you're powering it from the 12V accessory panel or from the in-cab fuse panel, you may be picking up more noise. Running your hot lead directly from the battery will help. Additionally, mounting it on the bumper does not provide a very good "ground plane" for the antenna. The roof or front fender mount are better options. Have you tuned it with an SWR meter?

 

depends here...

Is the noise a whining or a popping sound?

If it is whining, you are getting noise from the alternator. Typically, a capacitor is going out in the alternator.

If it is a popping sound, look in the ignition for a bad cap/rotor or a plug or plug wire. Most likely a wire.

 

Add a noise filter to the power feed:



And consider running a dedicated power (and ground) feed from the battery to the radio, twist the wires as they run back from the battery to minimize noise. May also want to check the grounding on the antenna, sand away the paint where it attaches and/or add a ground strap to a good solid ground point. Poor grounding can cause noise AND high SWR readings.

And possibly pop for a better radio. I find inexpensive radios are noisy, better radios are quieter and will also have "Noise Blanking" and/or "Automatic Noise Limiting" type functions that will cut out most engine/ignition noise. I used to run a combined AM/FM/CB radio in my 4Runner but it was just too noisey with the engine running. Solved that problem by moving that radio to my diesel (no electrical noise at all) and got a better radio for the 4Runner (EFI is noisey).

 

Alright, so I have tried all of your suggestions. I grounded the antenna better and ran the wires to the battery, still get that same whining noise.

So in hopes it was a faulty radio I bought a Cobra LTD Classic with Sound Tracker. It seems to be a bit better but still there none the less. I tuned it using an SWR meter.(my dad does this professionally, yet he can't figure out my problem either)

Any more thoughts?

 

SWR will only realy affect transmission. Did you add a noise filter to the power leads? Was the wire you ran to the battery just for power or did you run a ground as well? If so, did you twist the power and ground wire together?

 

I got a $8 filter from advane auto, it was like night and day.

Lamm

 

I ran both a power and a ground wire to the battery, not sure what you mean by twist them together.

I was told that if you unscrew your coax, and the noise dissapears its coming through the antenna. I did this and the noise dissapeared. Which I'm told is where it begins to get more complicated.

 

How/where did you run the coax? Is it up against other wires? I'd echo the sentiments above and try a filter...

 

Alright,

So I think I have it fixed. I moved the location of the CB and re ran the coax so that it wasn't near any power wires. I grounded out the antenna better and checked all my grounds. The engine noise seems to be gone! !!! Hopefully it is and it stays gone.

Thanks for your help guys.

 

Good job!

 

Twist the power and ground wire around each other:



This can help to keep EMI from getting into the power/ground leads since this keeps the wires close together and they partially shield each other.