Chuck-The-Ripper

What is the brain you guys are referring to? I have a cobra 75 I bought new and I've never seen it?

texascodmw3

Actually, all the 'brains' for the Cobra 75 are in the mic. The little silver box is just a junction box.

I used a 75 for a little while in my JK. I liked the ultra small form factor, but I was very disappointed in its performance and replaced it with a Uniden when all attempts to address my issues failed.

FWIW, I'm an extra class ham and was an RF engineer in my previous career. I don't like the fact that the full RF output power is generated in the mic and must travel the little curly mic cable which has a very small coax inside. Small coax does not perform as well as larger coax. Just a little antenna mismatch or not-so-good grounding and you will have RF radiating from the mic cable. That is not good as that cable is right there with your dash components and wiring. I love the compact concept but it sacrifices more optimal RF design and performance.

Each installation can be different and the causes of the 'stray RF' that is interfering with your Jeep or other aftermarket systems can vary.

Grounding is key for the antenna as others have noted.
Try grounding the silver junction box.
Ensure you have a low SWR
Maybe relocate the junction box if possible
try ferrite beads/chokes on the power wires in case RF is getting induced into there.

I hope you get yours working and without too much more trouble.

gingerchocolate

There's a lot of great info coming up in this thread.

I didn't realize the RF was being generated in the handheld unit. Wow.

The junction box need to be grounded. So you need to mount it to a grounded surface or add a ground wire.

I'm sure you've already check this but make sure that your antenna mount it put together correctly and that insulator washer is actually doing its job.

As mentioned before nearly everything needs to be grounded with braided ground wire. (Bonding)

Frame to body, aftermarket numbers, I would add an additional strap to the hood. Ground the exhaust, add a strap to both sides of the engine.

Especially add a ground to the tailgate of you've mounted your antenna to it.

You should ground everything you can. A proper bonding should take hours.

Here is some really great info on bonding.
http://www.k0bg.com/bonding.html

Scuba_JKU

So I put another Cobra 75 in to make sure it wasnt the radio and I am still having the issue. Checked the antenna, not shorted and properly grounded. I have a Viper alarm/remote start installed. Dont know if this has anything to do with it.


Please someone helped. Heading to the trail tomorrow and I want to make sure my CB is working properly and is not gonna kill my jeep.

gingerchocolate

Did you ground the silver junction box?

Did you add any bonding? At the very least the tailgate needs to be bonded.

What antenna, antenna mount and coax cable are you using?

I cannot stress enough that the Jeep needs to be bonded (grounded) all over the place.

Did you use a voltmeter to make sure you don't have a short on your coax cable?

borderline homeless

I mounted my 75 yesterday to the metal plate in front of the steering coulmn by bolting it. I did not have time to wire to the battery so I just put a cigarette adapter on it and ran it and the mike cable out of the dash. Used it all day with out the issues you guys are experiencing.