So an problem that has popped up in the last 3 weeks or so on my 1994 Jeep Cherokee is some rather annoying ignition noise on the RX side of any VHF mobile radio mounted in the car.

Doing some investigation, I have figured its only when the engine is running (duh) and not in ACC or simply ON. That rules out the fuel pump. Its there even if I connect it to a separate battery not connected to the car electrical. I tried putting on RF chokes on power and antenna lines and no dice there either. Per suggestions from local Jeep guys, I tried grounding the hood and even the muffler without any success.

I checked the spark plugs and wires; all is good there and I didn't expect anything since they were replaced in May.

I'm totally stumped here; I have never had this issue before so I am running out of ideas. Locally, I found one other XJ owner who had a similar problem and ended up using noise supression plug wires and that solved the problem. Any else have any suggestions before I do that?

 

by vhf do you mean cb does it get its power from the xj if so try running ground from it and pos direct to bat connections

 

I'm a ham and well also involved in Search & Rescue and VHF is our primary band for communication. I haven't checked yet if it CB is also affected; but it would not surprise me.

I am already running a direct line to the battery positive terminal along with a ground connection.

 

Hey, fellow hammer here (AJ4AR.) Are you running the ground all the way to the battery, or to the body close to the radio? Are you using a mag mount, glass mount, or a mount that has a good ground connection to the body? Do you have plenty of space between all wiring for the radio and any other electrical systems in the jeep?

 

I am using 3 types of antennas. There is a front fender L-bracket that's directly connected to a Motorola Maxtrac. There is roof NMO mount on the roof that is connected to a Yaesu FT7900. The magmount on the rear is for APRS and is connected to a little handheld.

The ground I am using is a 0 gauge wire using a ground point the previous owner created under the seat for a stereo amp. I have all components under the rear seat with a little terminal strip distributing power.

 

Hm, well it is recommended typically to run your ground cable straight to the battery, that's mostly to prevent a ground loop though which would be giving you a whine primarily in your transmitted signal. What exactly does it sound like? It could be ignition pulsing, injectors, fuel pump, or any number of fan motors too... How well did you ground the exhaust, as well? One ground strap isn't always enough for that.

 

Oh hey, looks like I got a bit carried away with myself and forgot what all you said in the original post. (it happens lol)

Exactly where and how did you put a bead on the power line, and what composition was it? Not all ferrites are equal, you should be using either a mix 43 or a 31.

 

I'm using some radioshack ferrites. I placed them right after the battery line and right before the power terminal block.

 

I have the same problem with my CB and had a radio shop look at it. They wired direct to battery. They were thinking it was the ignition or plug wires. I'll be upgrading my stock wires in a while and see if that helps. I doubt it will, but that's something to try...

 

I have taken the Maxtrac and have directly connected the radio to the battery with clips and it's still there.

 

Sounds like it could be a bear on you. I had a friend with an RFI problem that took him a months to track down!

I'm not sure how much research you've put in to it, but http://www.k0bg.com/noiseid.html is a good start to IDing the noise for sure, and there's other pages on his site on dealing with it, including bonding/wiring/choke guides. Good luck!

 

I have looked at that website. It kind of sounds like a harsher version of the fuel injector recording.

 

I ended up figuring out its defenetly noise from the ignition system; I tuned to the VHF Air band and there it was loud as day all across the band.

I also up picking up some inexpensive (25.99) noise suppression type plug wires and the noise is about half as loud as before.