Strider

Hey, Happy Labor Day to everyone. I've got a question for you techs out there. I just installed a Cobra 19 Ultra CB in my 15 JK. I'm useing a 4ft fiberglass antenna mounted to the top of my 3rd break light to get it above any vertical sheet metal so it won't reflect back to the antenna. I have the Cb plugged into the cig lighter for power. My question is when the engine isn't running it's pretty quite, when the engines running I get some noise. I'm thinking of running a RF filter but when I talked to the electronics store (not Radio Shack a real electronis store) I was told they have a few RF filters and sometimes one will work where in the same situation the others won't. I was told Fords are notorious for noise,but other brands not so much. She says its a crap shoot. So my question is if you have a CB in a JK and use an RF filter which filter do you use? I don't want to hard wire it to the battery as I will only be using it once in a while. Thanks for the help.

Strider

One more quick question, will I have to ground the CB to the body. I have it mounted in my cup holder. I used this same unit in my car and it worked fine there but I had a magnetic antenna that stuck to the top of the car. Good ground plane and great reflection. Not so with thw JK. Thanks again.

jchappies

I would be sure the CB has a VERY GOOD ground and you tune the antenna with a SWR meter then if that doesn't work try ferrite beads

KCCO JK

Wish I could give ya a solid, definitive answer, nut electronic noise is a tough one. It really depends on the type of noise being generated. An rf filter however.. ehhh.... I would think a power regulator or capacitor filter would be a better fit, as that is where your noise is coming from. And for that, there are a few options, the best of which being a basic capacitor filter. Of course, thats not the technical name for it, but my brain is shutting down right now lol.

banditof2001

Sounds like you may have a ground problem causing a ground loop which maybe causing the noise. That would explain why it's quiet when the engine is off and noisy when it's on. Also, you may have to run a ground wire from your antenna mount to your body/frame. I've had to do that before too.

psouza

Some noise in an operating vehicle is to be expected. You fail to inform us of what type of noise it is or its severity, or even if it is more than normally expected in a JK.


Not much to go on, so a general procedural outline is offered.

Try some simple logic here.

You have noise. You want to know where it comes from, so MAYBE you can remove it.

So, how does noise get into the radio?

Most times the noise is radiated by the wiring of the vehicle by one or more subsystems, and picked up by the antenna.

Remove the antenna connector from the radio. Does the noise go away? If yes, you know that it is NOT coming in through the power line or power ground and is received by the antenna system.

If no, then the noise is coming in thru the power line or ground. An inductive, off the shelf noise filter may fix it or connecting your radio directly to the battery positive and ground (as you should have from the first) may fix it.

Reconnect the antenna cable at the back of the radio and then disconnect the antenna from the cable at the base of the antenna. Is the noise there? If yes, then the noise is being radiated into the antenna CABLE by some part of the vehicle wiring. Re route antenna cable. This is an unlikely possibility but it can happen.

At this point you should know if your installation is the cause of your noise. Probably, it is not, and you still have noise.

What subsystem of the vehicle is radiating the noise? Your possibilities are in order of most likely are...Fuel pump, vehicle computer hash, alternator, and ignition.

If the noise comes from the fuel pump, this will be the most difficult to kill. Things to try: Bond exhaust pipe to frame with strap. Try several places. Check bonding of the hood. Is the strap still intact? If bonding does not bring joy, a noise trap (low pass filter) will be needed as close to the fuel pump motor as possible. There are no certainties that this noise can be completely eliminated unless a full military EMI counter measure suite is implemented.

If noise is coming from the computer system, you are more or less screwed. Re locating the antenna may help.

Alternator diodes do generate RF noise by their switching action but it is generally lower in frequency than CB and not very strong. It generally will be conducted via power wires to audio devices and not radiated via air. Simple / common filters are effective when properly installed. Alternator field excitation via brushes (if equipped) can cause noise that is radiated from several places. CARE should be exercised here and seek professional help.

Ignition interference is generally not an issue in modern vehicles unless some ignorant nimrod has replaced spark plugs with non resistor types and or (if equipped with wires rather than coil rails) changed to non resistor wire loom. This fix is obvious. Sparking, deteriorating ignition wires are a possibility also. This fix is obvious.


This gives a perspective on how and where to start.
Good luck
Phil

Strider

Thanks for all the help. I found out where all the noise was coming from, I used a quick disconnect antenna mount for the antenna. I removed the quick disconnect mount and the buzzing went away. Go figure. Thanks again.