Engine RPM noise on CB radio

[K9DAK]

This points me towards the fuel injectors. With my VWs, the ECU can basically turn off (or just tickle them open) the injectors under closed-throttle (engine braking) conditions. Not sure how you'd fix that, however.

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.

 

[secretspy711]

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

Yes, and that reduces it. But it never goes away unless I turn the squelch up to what I believe is an unacceptably high level, or press the LO/DX button to reduce the receiver's sensitivity.

To be clear, this hasn't proven to be a problem when on the trail with other Jeeps, which is how I primarily use the CB. I just turn up the squelch high enough and I seem to be able to hear everyone in the group, and they can hear me. I don't hear the engine noise when another Jeeper in the group is talking. The problem is driving around town, I want to be able to pick up transmissions from as far away as possible. Why? I don't have a good answer for that. Because I like my stuff to work well. Maybe I just need to come to grips with the fact that this is as good as it's going to get using 60 year old tech, and use a mobile ham radio instead to scratch whatever itch this is.

I spent a couple hours today cleaning all the battery contacts, and probing for RFI with the engine running using a sniffer coil and listening for noise on the CB. Sweeping all around the engine bay I couldn't find anything. Nothing at the tail pipe either. I have access to a HackRF through work, so I might try that and see if I can learn anything by visually looking at a spectrum analyzer.

I found a bolt near the CB that is connected to ground. I took a wire and connected it between bare metal on the CB chassis to that bolt. No difference. I also tried connecting the negative power lead to that bolt. Also no difference.

I checked resistances all over the place, and it all seems to be very well grounded. Tail pipe to antenna mount barely even registered on my ohmmeter.

 

[prcguy]

The last ignition noise problem I looked at was a friends highly modified Toyota 4-Runner with aftermarket ignition stuff. His noise was so bad it made it difficult to use a 2m FM radio in the vehicle and HF/CB was impossible.

It was real obvious where the noise was coming from using a portable AOR8200MKIII receiver starting in the AM broadcast band with its built in antenna then going to a very short BNC whip to sniff near the 2m ham band. The noise was highest around the distributor and the spark plug wiring and distributor to coil wire.

We temporarily covered all that stuff with aluminum foil and the noise went down to an acceptable level. I gave him some braided tubing and he successfully covered most of the wiring with braid and life was good.

If you can't pinpoint your noise and since it sounds like the ignition system causing it, you could temporarily cover the ignition wiring in aluminum foil and see if the radio in its current setup can tell the difference.
prcguy

Yes, and that reduces it. But it never goes away unless I turn the squelch up to what I believe is an unacceptably high level, or press the LO/DX button to reduce the receiver's sensitivity.

To be clear, this hasn't proven to be a problem when on the trail with other Jeeps, which is how I primarily use the CB. I just turn up the squelch high enough and I seem to be able to hear everyone in the group, and they can hear me. I don't hear the engine noise when another Jeeper in the group is talking. The problem is driving around town, I want to be able to pick up transmissions from as far away as possible. Why? I don't have a good answer for that. Because I like my stuff to work well. Maybe I just need to come to grips with the fact that this is as good as it's going to get using 60 year old tech, and use a mobile ham radio instead to scratch whatever itch this is.

I spent a couple hours today cleaning all the battery contacts, and probing for RFI with the engine running using a sniffer coil and listening for noise on the CB. Sweeping all around the engine bay I couldn't find anything. Nothing at the tail pipe either. I have access to a HackRF through work, so I might try that and see if I can learn anything by visually looking at a spectrum analyzer.

I found a bolt near the CB that is connected to ground. I took a wire and connected it between bare metal on the CB chassis to that bolt. No difference. I also tried connecting the negative power lead to that bolt. Also no difference.

I checked resistances all over the place, and it all seems to be very well grounded. Tail pipe to antenna mount barely even registered on my ohmmeter.

 

[secretspy711]

Haven't been able to work on this lately, but I ordered 20 feet of 1/2" flat braid cable and some ring terminals to make up some proper ground straps. The plan is to go nuts. I've been reading through some of k0bg.com and picked up some good tidbits. I'll improve the tailgate strap since right now it's quite long and made of round wire. I'll also strap the hood, exhaust, roof rack, tub-to-frame, and also one directly from the battery to the tub (there should be one of those already, but as I understand it, it was designed for DC grounding, not RF). I also bought some mix-31 ferrite beads to make an RF-choke on the coax to hopefully eliminate common-mode current.

 

[SCPD]

Your problem is the radio is Grounded to the battery.
Make Ground to the frame or seat bolt and the noise will go away!
Short as possible is key.
Keep antenna away from engine.

 

[SCPD]

https://www.youtube.com/watch?v=TrrZyyiJln0

Move it to 1:54 to see visually how a ground should look.

 

[mmckenna]

Your problem is the radio is Grounded to the battery.
Make Ground to the frame or seat bolt and the noise will go away!
Short as possible is key.
Keep antenna away from engine.

See post #22, he already tried that, but it didn't fix it. It's radiated ignition noise picked up by the antenna. With the antenna mounted on the spare tire mount, he can't get it any further away from the noise source, so he's going to have to find the issue and fix it. Probably won't be easy/cheap, unfortunately.

 

[prcguy]

It won't go away if you do that.
prcguy

Your problem is the radio is Grounded to the battery.
Make Ground to the frame or seat bolt and the noise will go away!
Short as possible is key.
Keep antenna away from engine.

 

[SCPD]

Please, take a picture of how you grounded it.

 

[FiveFilter]

I've been lucky with my 2003 Jeep Wrangler.

I plop a 35-inch K30 magnet mount antenna in the middle of the hood, bring the wire in through the passenger front window to a little Cobra 19 radio, plug the radio into one of the 12v factory outlets, and am able to communicate without any RF interference except nominal AM background buzz which the squelch handles well. SWR about 1.3. Communicating range several miles, as expected.

Since I only use the radio when needed in my Jeep (read: not very often), I remove it and the antenna until the next time. It takes me a minute or two to install / uninstall the setup.

So, the interference is not necessarily a "Jeep" thing. Of course, my 15-year-old mud crawler doesn't have all of the newest gizmos on it. I understand that a lot of the new-and-improved stuff on new cars is sometimes RF noisy, including some of the LEDs so popular nowadays. However, I've added some LEDs myself outside-and-inside my Jeep without experiencing any RF interference.

As I said, I've been lucky.

 

[secretspy711]

Here's some shots of my installation.

 

[secretspy711]

couple more.

 

[secretspy711]

I got the HackRF SDR from work and sniffed around while looking at the entire CB spectrum and waterfall plot. Couldn't tell any difference between engine on vs off. Very disappointing -- I expected to see *something*. I can definitely see, however, when I key the mic, exactly what frequency it's transmitting on. There's a nice sharp spike at 27.205, right at channel 20 where it should be. Really neat little device, if you have a chance to play with any SDR, it's pretty interesting.

In light of that, I decided to start making up some ground straps anyway. I replaced my long groundstrap on the tailgate with a short one, and also put 2 on the hood, and 3 on the exhaust. I feel like maybe it helped a tiny bit, but it could just be my imagination.

 

[secretspy711]

Hard to see in the photos but there are star washers under the ring terminals And the terminals are soldered.

According to K0BG, I should *not* wire-brush through the zinc layer on the frame to expose bare metal. I assumed this was also true for the areas where I'm going through painted sheet metal.

Bonding

 

[krokus]

Hard to see in the photos but there are star washers under the ring terminals And the terminals are soldered.

According to K0BG, I should *not* wire-brush through the zinc layer on the frame to expose bare metal. I assumed this was also true for the areas where I'm going through painted sheet metal.

Bonding

You want to apply a corrosion inhibitor to those connections, too. Cleaning up the rust at the antenna mount and spare mount would be a good idea. (Corrosion is a non-linear junction, which leads to IMI.)


Sent using Tapatalk

 

[secretspy711]

You want to apply a corrosion inhibitor to those connections, too. Cleaning up the rust at the antenna mount and spare mount would be a good idea. (Corrosion is a non-linear junction, which leads to IMI.)

I will do that. It looks rusty around the hardware but underneath it's much better. I should have bought the stainless version I guess.

I had to google that one... IMI = inter-modulation interference?

 

[krokus]

I should have bought the stainless version I guess.

I had to google that one... IMI = inter-modulation interference?

Stainless is a good idea, unless strength/hardness of regular steel is needed.

You got IMI correct. The signals mix with each other, and their products mix with each other, and the original signals. It can get nasty, in a hurry.

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[secretspy711]

little more troubleshooting...

In my earlier test with a separate battery, I left the antenna attached to the tailgate mount simply because I knew it wouldn't be a valid test if the antenna didn't have a groundplane to work with. I thought maybe that was a bad test since the radio's ground wouldn't be the same as the antenna's ground.

So today I decided to repeat that test, but with everything completely disconnected from the vehicle, including the antenna. To get around the groundplane problem I fashioned a makeshift dipole from my 2 firestik antennas. (One connected normally, with the other pointing in the opposite direction with the base in contact with the coax connector barrel.) I just held it like this in my hand at the feedpoint. When I brought it close to the engine, I did pick up the same noise. As I stepped back, the noise went away. I was also able to pick up some noise near the rear of the vehicle, but this was hit or miss. This tells me that my problem (or at least some of my problem) is 100%, without a doubt, radiated RFI. It could be caused by current flow on parts that are not well bonded though.

I tried touching a wire from the alternator to the battery, and that didn't seem to help at all. (But I haven't tried doing that with a true ground-strap torqued down.)

I'm thinking maybe I will go visit a CB shop on Friday and see if they have any other ideas. Short of adding more ground straps, I'm fresh out.

 

[prcguy]

You can do the exact same test but instead of using two whips as a dipole, take about 6in of insulated wire, wrap it into 2 or 3 small turns and attach the wire across the coax connector center pin and ground. You then have a small pickup loop that you can probe around the engine compartment and hopefully pinpoint the specific noise maker.
prcguy

little more troubleshooting...

In my earlier test with a separate battery, I left the antenna attached to the tailgate mount simply because I knew it wouldn't be a valid test if the antenna didn't have a groundplane to work with. I thought maybe that was a bad test since the radio's ground wouldn't be the same as the antenna's ground.

So today I decided to repeat that test, but with everything completely disconnected from the vehicle, including the antenna. To get around the groundplane problem I fashioned a makeshift dipole from my 2 firestik antennas. (One connected normally, with the other pointing in the opposite direction with the base in contact with the coax connector barrel.) I just held it like this in my hand at the feedpoint. When I brought it close to the engine, I did pick up the same noise. As I stepped back, the noise went away. I was also able to pick up some noise near the rear of the vehicle, but this was hit or miss. This tells me that my problem (or at least some of my problem) is 100%, without a doubt, radiated RFI. It could be caused by current flow on parts that are not well bonded though.

I tried touching a wire from the alternator to the battery, and that didn't seem to help at all. (But I haven't tried doing that with a true ground-strap torqued down.)

I'm thinking maybe I will go visit a CB shop on Friday and see if they have any other ideas. Short of adding more ground straps, I'm fresh out.

 

[cmdrwill]

" I was also able to pick up some noise near the rear of the vehicle, ".

Maybe a noisy electric fuel pump, they are in the gas tank.