Troubleshooting Electrical Noise

papageoff · June 1, 2017

I recently installed a CB radio into my truck. I'm transmitting well, and I've got good SWR levels. My problem is I don't receive all that great. I have a lot of static and noticed a rhythmic ticking that varies with engine speed (when running) and disappears when the engine's off. It's pretty clear I'm getting some electrical noise. I just don't know if it's from the antenna side or the radio (power) side.

I've got the antenna mounted to the toolbox with a ground wire from the box to the frame at the factory gas-filler-nozzle ground point.

I've got the radio (+) wired to the battery via a relay in the cab triggered by the RAP signal from the box under the brake pedal. The ground comes back out the firewall and connects to the ground stud the engine uses. I think this might be my problem, but I hate to re-terminate that wire to test.

Like I said, the radio is transmitting well (per my radio checks), but I don't hear others well. I'm inclined to think the problem is in the power-side of the equation, but am interested in your opinions.

Heavy 5.7 · June 1, 2017

am interested in your opinions.

A cap could choke the noise but is the radio itself junk?

papageoff · June 1, 2017

I don't think so. It's a brand new bearcat 980ssb.

I have thought about adding a filter cap, but I would still like to find the source of the noise.

I did some playing with the meter and I have 0-ohms between the antenna (ground side) and the toolbox, and 0-ohms between the box and gound screw as well as other random spots like the rear door latch. It doesn't really rule out reception of noise but it does mean I have a good antenna ground.

So I'm fairly sure it's on the radio power supply at this point. But, I might try disconnecting the antenna and see if I still get the noise.

Heavy 5.7 · June 1, 2017

The reception static disappears completely when the engine is off?

papageoff · June 2, 2017

Not completely, but it's significantly lessened. I'm going to try new grounds on the antenna and radio this weekend. I'll test in between and will start with the radio because I know I have an electrical noise problem and it seems the most likely source.

Heavy 5.7 · June 2, 2017

You may want to try that rig in another vehicle just for yuks.

sdeeter19555 · June 2, 2017

To isolate the noise, disconnect the antenna while the truck is running (just don't try to transmit). If the noise goes away or subsides, it's from the antenna side, if not; it's from the power side.

If you have excessive noise while the truck is off, then you may have a noisey receiver. If you're not hearing anything, you could have a deaf receiver.

Newer radios are typically sucky from the box and need tuned. I've not found a decent new radio yet...at least not one you buy from a local store.

For what it's worth, I have alternator whine...I can even hear it in the AM side of the factory AM/FM radio. Mine is power related.

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papageoff · June 2, 2017

To isolate the noise, disconnect the antenna while the truck is running (just don't try to transmit). If the noise goes away or subsides, it's from the antenna side, if not; it's from the power side.

If you have excessive noise while the truck is off, then you may have a noisey receiver. If you're not hearing anything, you could have a deaf receiver.

Newer radios are typically sucky from the box and need tuned. I've not found a decent new radio yet...at least not one you buy from a local store.

For what it's worth, I have alternator whine...I can even hear it in the AM side of the factory AM/FM radio. Mine is power related.

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I know that when I disconnect the antenna, I get nothing signal wise. I don't remember if I have listened for the electrical noise. If changing these grounds doesn't work, I'm probably going to try my buddy's radio and see how it performs. If it's the same it's the truck. If there's a difference, it's my radio.

It works well enough for short range, but if people start getting more than a mile or so away, I can't hear them clearly. They hear me loud and clear for miles and miles on SSB. I only really got it for short range comms with buddies off-road, but my inner perfectionist wants ALL the range. ;)

sdeeter19555 · June 2, 2017

Keep in mind an electrical ground is not the same as a RF ground.

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papageoff · June 2, 2017

Keep in mind an electrical ground is not the same as a RF ground.

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Wilco. I studied a lot of AC/DC/RF ET stuff in school, but I have little practical experience with RF. I know theory, but the practice has been a learning curve.

diyer2 · June 2, 2017

My guess is power cable, positive + side alternator noise.

papageoff · June 4, 2017

Well, I tinkered with this last night in the driveway. I couldn't get it to make the electrical noise, but I know I'm not crazy as a buddy heard it the other day too. For S&Gs, I moved the radio ground to the negative battery and saw no difference in signal-noise ratio. So, I put it back as where it was the wiring was cleaner.

Then, I made a new 10GA ground wire to go from the antenna mount bracket to the frame directly. Previously, I grounded the toolbox the antenna mounted to. That also made no apparent difference. One last thing I might try, (but I'm not eager to is to replace the firering cable with a traditional PL-259 that has more insulation.) I'm not convinced these firering cables are all that great. The connections from the coax to the ring-terminals are rather weak. It's like wire soldered to a washer.

I'm going to meet up with a buddy on Monday or Tuesday who's got a radio in good order. We're going to swap radios and see what happens.

papageoff · June 5, 2017

So we swapped radios and got similar results in both vehicles on both radios. I guess at this point I just have to accept it works as well as it's gonna.

It was interesting how his radio is better at rejecting noise than mine. I guess it has a better reciever built in. It also has a front firing speaker. I may have to upgrade.

papageoff · June 6, 2017

On the way home we did some more testing to see how far we could get. We basically drive the opposite way on the same road for 10+ miles each so it's a pretty decent test.

We got about 18 miles on SSB before we could no longer make each other out, but as usual, at that point, I was still clear enough to him, but I could barely make him out. That kinda confirms my suspicion that my radio works, it's just his has better reception.

Oh, and the electrical noise was back. I've determined that's coming from how the wires are routed and stuffed behind it. I fiddled with it and was able to remove most of it. So, I'm calling this project done until the new amplified PA speaker comes, that is...

sdeeter19555 · June 6, 2017

What radio does he have? Has he had any work done on it? Find a GOOD tech, and have your radio aligned...a lot of them are barely on frequency, especially talking the SSB side of the world. Around here, it would be Bob's CB shop in Strattanville, PA.

Does he have the same antenna? I think your distance issue is antenna and mounting location. I have a Wilson 5000 in the center of the roof, 1:1 SWR, and can easily talk 10 miles barefoot...in all directions.

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