Engine RPM noise on CB radio

I've installed a Uniden CXM760 in my Jeep Wrangler Unlimited. My problem is that I hear noise corresponding to engine RPM over the radio. When the engine isn't running, the noise goes away. But when I'm driving, I have to turn the squelch to a setting of 4 or 5 (max = 7) to stop the noise. Turning up the squelch effectively reduces my range, doesn't it?

Another "workaround" that seems to work is by pressing the LO/DX button. Pressing this once turns on "local1" and quiets the noise somewhat, but does not eliminate it. Pressing it a 2nd time turns on "local2" and the noise disappears and I can turn the squelch all the way down to 1, and the noise is still gone. But doesn't this severely limit my range? I don't think this is the intended purpose of that button.

I'd rather fix the real problem rather than use these workarounds, but of the two, is it better to turn up the squelch, or turn on local2 and turn down the squelch?

I've tried everything I can think of. The CB itself is mounted in the passenger-side footwell.
1.) Power and ground to the CB is wired directly to the battery.
2.) Coax is routed from the CB, along the passenger side floor under the carpet, across the tailgate hinge, to a mount attached to the spare tire holder.
3.) I have a ground strap running from one of the antenna mount bolts, across the tailgate hinge to the body tub using a self tapping screw. The presence of this ground strap does not seem to make a difference though. I've scraped off the powder-coat on the mount to ensure a good ground.
4.) SWR is good. 1.0 on channel 20 and ~2.0 on 1 & 40.
5.) I've tried 2 different antennas (Firestik and Firefly, both 3-foot). I also have a 4-foot Wilson Flex that I haven't tuned yet, but connecting this one still produces noise.
6.) I put ferrite chokes on the power leads.
7.) I tried powering the CB from a completely separate battery sitting in the passenger seat, and the noise is still there while driving.
8.) When I disconnect the antenna, the noise goes away.
9.) I bought new RG8X coax and hooked it up, without tucking it under the carpet. Made no difference whatsoever.

#7 and #8 are telling me that the noise is coming in through the antenna, and not the power leads.

Is there anything else I can try? Banging my head against a wall here.

What you are experiencing is alternator whine.... noise generated by the alternator that varies with the engine RPM. It comes in on your 12VDC supply line to the radio. Most auto parts stores, Amazon, etc. sell alternator whine filters for less than $15. Be sure you get one that includes a capacitor and coil as part of the circuitry, or is an active filter. A simple capacitor filter will not work.

secretspy711 said:

I've installed a Uniden CXM760 in my Jeep Wrangler Unlimited. My problem is that I hear noise corresponding to engine RPM over the radio. When the engine isn't running, the noise goes away. But when I'm driving, I have to turn the squelch to a setting of 4 or 5 (max = 7) to stop the noise. Turning up the squelch effectively reduces my range, doesn't it?

Click to expand...

Yes. Reduces the ability to hear weak signals.

secretspy711 said:

Another "workaround" that seems to work is by pressing the LO/DX button. Pressing this once turns on "local1" and quiets the noise somewhat, but does not eliminate it. Pressing it a 2nd time turns on "local2" and the noise disappears and I can turn the squelch all the way down to 1, and the noise is still gone. But doesn't this severely limit my range? I don't think this is the intended purpose of that button.

Click to expand...

Yes. It's reducing the receiver gain.

secretspy711 said:

I'd rather fix the real problem rather than use these workarounds, but of the two, is it better to turn up the squelch, or turn on local2 and turn down the squelch?

Click to expand...

Depends.

secretspy711 said:

I've tried everything I can think of. The CB itself is mounted in the passenger-side footwell.
1.) Power and ground to the CB is wired directly to the battery.
2.) Coax is routed from the CB, along the passenger side floor under the carpet, across the tailgate hinge, to a mount attached to the spare tire holder.
3.) I have a ground strap running from one of the antenna mount bolts, across the tailgate hinge to the body tub using a self tapping screw. The presence of this ground strap does not seem to make a difference though. I've scraped off the powder-coat on the mount to ensure a good ground.
4.) SWR is good. 1.0 on channel 20 and ~2.0 on 1 & 40.
5.) I've tried 2 different antennas (Firestik and Firefly, both 3-foot). I also have a 4-foot Wilson Flex that I haven't tuned yet, but connecting this one still produces noise.
6.) I put ferrite chokes on the power leads.
7.) I tried powering the CB from a completely separate battery sitting in the passenger seat, and the noise is still there while driving.

Click to expand...

OK, that's some good troubleshooting. So, unlikely the noise is coming through the power feed.

secretspy711 said:

8.) When I disconnect the antenna, the noise goes away.

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OK, so that means that it's coming in the antenna, or it's possibly a grounding issue. Try running a short ground wire from the radio chassis to the vehicle body, keep the wire as short as possible. Do not rely on the mounting bracket as the ground.

secretspy711 said:

9.) I bought new RG8X coax and hooked it up, without tucking it under the carpet. Made no difference whatsoever.

#7 and #8 are telling me that the noise is coming in through the antenna, and not the power leads.

Click to expand...

Yes, I agree on the surface, but it's hard to do this all remotely.

secretspy711 said:

Is there anything else I can try? Banging my head against a wall here.

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A couple of things:
Like I said above, ground the radio chassis directly to the body.
Try moving the antenna.
If you have a portable CB, start the Jeep and walk around to see if you can locate the noise.

Fighting RFI in a vehicle can be difficult. Some vehicles are just noisy.

popnokick said:

What you are experiencing is alternator whine.... noise generated by the alternator that varies with the engine RPM. It comes in on your 12VDC supply line to the radio. Most auto parts stores, Amazon, etc. sell alternator whine filters for less than $15. Be sure you get one that includes a capacitor and coil as part of the circuitry, or is an active filter. A simple capacitor filter will not work.

Click to expand...

Not sure, mainly because of this:

secretspy711 said:

7.) I tried powering the CB from a completely separate battery sitting in the passenger seat, and the noise is still there while driving.

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hi popnokick, did you read all of my numbered points, specifically 7 and 8? I really do not think that it's coming in through the 12v line.

I would not really describe the noise as a "whine." Although it does correspond to engine RPM, it's lower in pitch, more like a "buzz." I'll try to get a video of it.

Couple more suggestions I found that I'm going to try:
Ground the frame directly to the battery
Ground the exhaust to the frame, near the tailpipe

If it is a continuous high pitched whine, it is alternator noise. If it is "popping" that gets more rapid as the engine speed increases, it is ignition (spark plug) noise.

But many vehicles also have their engine computer in the passenger footwell, in the kick panel or under the seat. Those ECU's can also create electrical noise.

So the question is, what kind of noise is it?

If it is alternator "whine", pop is right, you can usually address that with a common alternator noise filter. That's often a capacitor and choke coil, but sometimes a 0.1mfd 20V capacitor is all you need to place across the power leads. Alternator whine CAN also indicate an alternator failure is coming, it is worth checking the system out not simply hiding that if you have that problem.

Since you say the noise is still there when you are not using the car's battery, as Mck said it should not be an alternator/power supply issue. That points to spark plug (ignition) noise.

Spark plug noise can mean it is time for new plugs, or coilover packs, or ignition wires. If you have traditional style ignition wires, test them on a multimeter. The center core, from end to end, should be under 500 ohms regardless of the cable length when new. As they age that will typically go to 10,000 ohms by five years--and that's well past the time to replace them. The increased resistance will also make them emit more ignition noise, and cut engine performance. Sometimes there's a condensor (capacitor) in the ignition system, which is there to clamp impulses and noise, and that's just gone bad or has a bad connection. I think separate condensors are obsolete on cars these days...hard to keep track.

Hopefully the problem is not the ECU, shielding that or adding filters could be more extensive.

Pressing the "Local/DX" button and putting the radio in Local mode just cuts the receiver sensitivity. So yes, it will cut noise--because it is cutting everything.

If your power lines are running alongside any ignition wiring, they could be picking noise up inductively. In that case, you move the wires, try to cross any harness wiring at an angle so you pick up less as well.

I'll add that I have the CMX-560, the little brother of this radio.

I've got it installed behind the seat of my Ford F150 Crew cab next to a VHF radio. Power is via a 6 gauge feed direct from the battery. Everything is grounded. Permanent mount NMO antenna on the roof.
VHF radio has zero noise.
The CMX-560 has a very slight buzz on the RX audio, imperceptible unless I have the volume cranked up way too loud.
I've done about all I'm willing to do to address it as I use it very rarely and it's imperceptible under normal conditions.
Grounding the radio chassis direct to the body didn't fix it.
A string of ferrites on the power, antenna and control head cables didn't fix it.
Permanent antenna in the center of the cab roof didn't fix it.

Since these radios are AM, it's just a reality that if there is any RFI, they are going to hear it.

The other possibility is that the noise is coming in through the RF deck to control mic cable. Rerouting that might be a good idea, too.

I'll try to address some of the questions and points that have been made. Thanks everyone for your help.

I'll try grounding the CB chassis, although I'd expect that the chassis should be grounded internally to the negative wire, which I've got hooked up directly to the battery negative terminal. Do I need to drill a hole in the case for this, or just put a lug under the 1 screw in the back?

I don't have a portable CB, but I can make an RFI sniffer by coiling up some wire, attaching it to center and shield, and probing around.

The power wires coming out the back of the CB look to be about 18AWG. I had to extend them quite a bit to reach the battery. Would heavier gauge wire do anything?

I'd say the noise is closer to a "popping" than a "whine". I would describe it more like a buzz. I might also add that it's a manual transmission, and when I let out the clutch and engine-brake, the noise characteristic changes to more like white noise. The buzz starts again when I give it some gas and increases in pitch with RPM.

It's a 2016 Jeep Wrangler, with 19,000 miles. I bought it brand new in September 2016. Not very old. I believe it has coil packs directly on top of the spark plugs, and does not have traditional spark plug wires. My understanding is that there's not much I can do here, is there? Isn't it way too early for the coil packs to be going bad?

The ECU is in the engine bay, front left corner of the jeep just behind the washer fluid. That's about as far from the CB as it can get. Here's a picture:
https://www.junglefenderflares.com/blog/wp-content/uploads/2016/10/jeep-jk-hemi-swap1.jpg

Sorry, missed #8 - "8.) When I disconnect the antenna, the noise goes away."
Alternator whine coming in through the DC line will persist even when the antenna is disconnected. So you are in fact looking for an RFI source that is entering via the antenna / receiver. Rred touched on this in his reply: There are diodes in alternators that when they have failed / near failed can generate RFI. If it's a full failure of one of those diodes it should be easy to detect with simple alternator diagnostics. But as Rred wrote, it may be a failure in the alternator that is in early stages and getting ready to happen... which might be harder to detect. Any way to replace your alternator on a test basis... and put it back if the old one proves OK?
One more thought... and this is a long shot but easy to check: Be sure you've unplugged every USB gadget in any 12V outlet in the vehicle. They are notorious for RFI of many different kinds. I wrote "long shot" because the RFI doesn't always mimic alternator whine and change in pitch with the engine RPM. But it's a simple check to pull out all your cellphone chargers, dash cam USB devices, portable powered refrigerator/food container, etc. to check.

Something like this should help: https://www.amazon.com/MFJ-1142-Lin...=1521747001&sr=8-15&keywords=12v+noise+filter

secretspy711 said:

I'll try grounding the CB chassis, although I'd expect that the chassis should be grounded internally to the negative wire, which I've got hooked up directly to the battery negative terminal. Do I need to drill a hole in the case for this, or just put a lug under the 1 screw in the back?

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Yes, there is "probably" a DC path between the radio chassis, the negative power lead and all the way to the battery.
The issue is that long wires act like antennas. Having a direct/short connection from the metal case of the radio direct to body ground can solve some issues. The idea is to remove the long "antenna" that's the power feed from the equation. You sort of already did that when you ran it off a separate battery, however there may be multiple ways noise is getting into the radio:
Through the antenna. -Try moving the antenna.
Through the coax. - If the radio is not well grounded, the RFI can be picked up by the coax. You want to give that a safe place to go by directly grounding the chassis and -not- creating another long antenna.
Through the power lead, but you kind of already proved that unlikely by running off the separate battery.
Through the control head cable, it can act like an antenna, it should be shielded, but making sure the radio chassis is grounded can help.

secretspy711 said:

I don't have a portable CB, but I can make an RFI sniffer by coiling up some wire, attaching it to center and shield, and probing around.

Click to expand...

That would work.

secretspy711 said:

The power wires coming out the back of the CB look to be about 18AWG. I had to extend them quite a bit to reach the battery. Would heavier gauge wire do anything?

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No. 18 gauge is plenty for a 4 watt CB radio. Going to larger wire size won't fix noise.

secretspy711 said:

I'd say the noise is closer to a "popping" than a "whine". I would describe it more like a buzz. I might also add that it's a manual transmission, and when I let out the clutch and engine-brake, the noise characteristic changes to more like white noise. The buzz starts again when I give it some gas and increases in pitch with RPM.

Click to expand...

Sounds like ignition noise, but with so many systems in modern vehicles, it could be a lot of things. Either way, it sounds like radiated noise. Grounding, shielding, etc. can help with that.

secretspy711 said:

It's a 2016 Jeep Wrangler, with 19,000 miles. I bought it brand new in September 2016. Not very old. I believe it has coil packs directly on top of the spark plugs, and does not have traditional spark plug wires. My understanding is that there's not much I can do here, is there? Isn't it way too early for the coil packs to be going bad?

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Something breaking is always possible. Assuming it's not broken because it's new is usually a recipe for disappointment. Everything should be suspect, but before you start replacing coil packs, find out where the noise is actually coming from first.

secretspy711 said:

The ECU is in the engine bay, front left corner of the jeep just behind the washer fluid. That's about as far from the CB as it can get. Here's a picture:
https://www.junglefenderflares.com/blog/wp-content/uploads/2016/10/jeep-jk-hemi-swap1.jpg

Click to expand...

The ECU's are pretty well shielded, and I'd be surprised if it was the cause.
What it can be is noise radiated by the vehicle wiring. Keeping coax, power and control head cables away from existing vehicle wiring can usually resolve this.

adamr368 said:

Something like this should help: https://www.amazon.com/MFJ-1142-Lin...=1521747001&sr=8-15&keywords=12v+noise+filter

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Probably not going to help. He already established that it wasn't getting in via the power feed. He disconnected it and ran it off a separate battery.

If the noise was coming in via the power feed, then it might work, but it's cheaper to just fix the issue rather than buying a box to hide it.

I would try a different CB as a test . Preferably one that has not been peeked and tuned and see if a different radio shows the same noise .

mmckenna said:

OK, so that means that it's coming in the antenna, or it's possibly a grounding issue. Try running a short ground wire from the radio chassis to the vehicle body, keep the wire as short as possible. Do not rely on the mounting bracket as the ground.

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Exactly. Run the radio's power ground directly to the body close to the radio. Disconnect the radio's 'ground power lead' from the battery negative terminal.

cmdrwill said:

Exactly. Run the radio's power ground directly to the body close to the radio. Disconnect the radio's 'ground power lead' from the battery negative terminal.

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I agree but I'd want to know for sure that the negative power lead is actually grounded to the radio chassis first. That's why I suggested grounding the radio chassis separately.

Reading through all the posts I would say the problem is spark plug/distributor type noise radiating into the air and it must be fixed at the source. The fact that the noise goes away with the antenna disconnected and running from a separate battery did not have any effect usually means changing grounding points or similar will not have any effect because the antenna is picking up the noise.

This type of problem is usually difficult to fix without a radical change to the ignition system.
prcguy

cmdrwill said:

Exactly. Run the radio's power ground directly to the body close to the radio. Disconnect the radio's 'ground power lead' from the battery negative terminal.

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I have had an issue with one of my Jeeps having a resistor in the lead from the negative post to the chassis. It took me awhile to sort out that it was intentional.

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Chronic said:

I would try a different CB as a test . Preferably one that has not been peeked and tuned and see if a different radio shows the same noise .

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The CXM760 (~$150) actually replaced a PRO505XL (~$30) that I still have laying around. I don't recall having this engine noise problem with that one, but since it was a much simpler radio, I always just turned up the squelch knob until noise was no longer heard, and went on my way. There was no real indication how high the squelch was set. I never drove around with the squelch low to see if there was any engine noise. I could certainly do that, but I don't think it would tell me much either way. In order to be a meaningful test I would have to try another CXM760 which I don't have. Putting the old 505XL back in might make the noise go away, but I would also need to test to see if the sensitivity (range) is the same as the CXM760. I suspect it's far less.

secretspy711 said:

The CXM760 (~$150) actually replaced a PRO505XL (~$30) that I still have laying around. I don't recall having this engine noise problem with that one, but since it was a much simpler radio, I always just turned up the squelch knob until noise was no longer heard, and went on my way. There was no real indication how high the squelch was set. I never drove around with the squelch low to see if there was any engine noise. I could certainly do that, but I don't think it would tell me much either way. In order to be a meaningful test I would have to try another CXM760 which I don't have. Putting the old 505XL back in might make the noise go away, but I would also need to test to see if the sensitivity (range) is the same as the CXM760. I suspect it's far less.

Click to expand...

Following the KISS principle: Have you turned on the automatic noise limiter (ANL)?

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