RF Gremlins Revisited - Possible Defective Radio, or Normal CB Shenanigans?

[Trevelayan]

My problems with this radio setup are detailed here

Additionally here

This probably seems like an odd question, but I realized while sitting in a grocery store parking lot, with my engine off and radio on, I can HEAR passing cars though the radio, via static matching their engine RPM.

I'm not even talking like a car right next to me, I'm talking cars driving 25-50 YARDS away. The volume grows in intensity when they approach, and fades as they move away. Once particularly egregious car I could hear about 70(!) yards away.

I can also hear powerlines, sub stations, traffic lights, and many other sources of electricity through the CB, so loud that with my Gain at 75%, I'm more or less constantly receiving static at a level of 2 out of 4 bars, which makes hearing people actually talking nearly impossible.

Initially I thought my truck was the problem, and this has happened with 2 different antennas. Is this normal CB behavior, or does my unit just have crap noise filtering? It's a Pro 520xl which I've seen highly recommended and the ANL is on, so before I dive into expensive repairs/changes to my truck to address excess RF, I want to be sure it's not the radio that's the issue.

 

[RFI-EMI-GUY]

I would have to say that your radio picking up noise from other vehicles and your shop lights is not concerning. I trust that the squelch and ANL circuits on the radio work properly. Vehicles radiate noise and a sensitive receiver will pick them up.

I would focus on the OEM AM radio problems first. How is the antenna installed, is it a fender mounted whip? If so, check to see that it is grounded properly at the fender and that the fender is actually grounded to the chassis and adjoining sheet metal. Has the vehicle been in an accident? Perhaps the bolts are not grounding properly because a fender was removed and resprayed heavily. There should be a bonding strap from the negative terminal of the battery to the body just a few inches away. Is that strap intact or is it corroded? Do you even have a good signal from your local station? Maybe the radio antenna is bad?

 

[Trevelayan]

I would have to say that your radio picking up noise from other vehicles and your shop lights is not concerning. I trust that the squelch and ANL circuits on the radio work properly. Vehicles radiate noise and a sensitive receiver will pick them up.

I would focus on the OEM AM radio problems first. How is the antenna installed, is it a fender mounted whip? If so, check to see that it is grounded properly at the fender and that the fender is actually grounded to the chassis and adjoining sheet metal. Has the vehicle been in an accident? Perhaps the bolts are not grounding properly because a fender was removed and resprayed heavily. There should be a bonding strap from the negative terminal of the battery to the body just a few inches away. Is that strap intact or is it corroded? Do you even have a good signal from your local station? Maybe the radio antenna is bad?

The antenna is as it came from the factory, fender mounted. There is a ground strip only about 3 inches long from the battery. When the truck is off and I'm away from RF sources, I can talk 5+ miles no problem. When the engine is running there is too much noise. I don't think it's an electrical grounding issue as I've been working on this for a while and that was one of the first things I looked into when I started trying to fix it. The noise goes away completely when the antenna is unplugged.

 

[prcguy]

If your AM radio was supplied stock with the vehicle and it now picks up ignition noise then something has changed in the vehicle and its making more noise now. That is a key point and more significant than the CB, which is user installed and subject to stuff.

The AM radio did not have noise in the dealer showroom. Get the vehicle ignition system and anything else that has been changed back to stock and the noise in the AM radio will go away, period, end of story. The CB might be noise free at that point or it may need additional attention.

 

[RFI-EMI-GUY]

When were the spark plugs last changed? Ford claims the plugs in my Expy are good to 100K miles. It is actually BS because at 36K miles I changed them and the gaps were huge. I put a nickle in them, they were that large. Huge gaps mean higher voltage on the wires and potential for misfires due to the insulation breaking down.

 

[Trevelayan]

When were the spark plugs last changed? Ford claims the plugs in my Expy are good to 100K miles. It is actually BS because at 36K miles I changed them and the gaps were huge. I put a nickle in them, they were that large. Huge gaps mean higher voltage on the wires and potential for misfires due to the insulation breaking down.

It's been 70k miles or so since the plugs were changed and probably 150k+ since the wires and distributor were changed. They probably need changed anyway so I'll get them replaced regardless.

 

[cmjonesinc]

I saw in the other thread you said it was a 5.9 so I'm assuming it's a Dodge? If so, and if you want to pm me the last 8 of your vin I'll be happy to check with Chrysler and see if there are any TSB's concerning bad grounding or related issues.

 

[WB9YBM]

"This probably seems like an odd question, but I realized while sitting in a grocery store parking lot, with my engine off and radio on, I can HEAR passing cars though the radio, via static matching their engine RPM...I'm not even talking like a car right next to me, I'm talking cars driving 25-50 YARDS away. The volume grows in intensity when they approach, and fades as they move away. Once particularly egregious car I could hear about 70(!) yards away."

I'm curious if there might be a problem with the noise limiter in your radio. Also have you checked to see if your radio chassis is grounded to the metallic parts of your car body? If the only place that you're getting ground is through the electrical system, maybe that might present problems. Also there are some sources that generate more noise than others: for example cars with a "race car" grade ignition system will generate a LOT more electrical noise than conventional systems.