Fluttering Sound (Interference) in VHF Radio While Engine Running

Interesting, thanks. I will check to see where my negative goes. Whatever I did, I remember asking on here first.

But, since this just started happening yesterday, and has not been a problem for the past two or three months, I suppose it wouldn't have to do with how I originally wired it, right?

It's probably not the cause but it's possible. It does sound like noise from the ignition/spark plugs.

A couple reasons. It could screw around with a vehicle's battery monitoring system. That's not an issue with TJs, and I know next to nothing about newer Jeeps, but it's something to keep in mind with modern cars. Second, if the battery's ground to the firewall or to the engine were to fail while the radio is connected to the battery's negative, all the current in the vehicle will go through the radio.
 
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It's probably not the cause but it's possible. It does sound like noise from the ignition/spark plugs.


A couple reasons. It could screw around with a vehicle's battery monitoring system. That's not an issue with TJs, and I know next to nothing about newer Jeeps, but it's something to keep in mind with modern cars. Second, if the battery's ground to the firewall or to the engine were to fail while the radio is connected to the battery's negative, all the current in the vehicle will go through the radio.
Thanks, we also put fuses on both wires. I did not come up with this on my own. This is the standard procedure that most of the hams in our club use so I just took their advise and I have never had a noise issue. I do appreciate you answering my question. I always try to learn new things and you bring up a valid concern.
 
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Thanks, we also put fuses on both wires. I did not come up with this on my own. This is the standard procedure that most of the hams in our club use so I just took their advise and I have never had a noise issue. I do appreciate you answering my question. I always try to learn new things and you bring up a valid concern.
Yup. Fused both sides. Never knew why, just followed the old protocol.
 
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Wiring straight to the negative side of the battery was the common wisdom for a long time, and to be fair, I don't know if it caused widespread problems, but modern thinking is that it's not a good idea.

When you think about it, nothing else grounds that way. Everything in the vehicle grounds to the chassis. Wiring a radio to the battery negative creates a single alternate path.
 
Wiring straight to the negative side of the battery was the common wisdom for a long time, and to be fair, I don't know if it caused widespread problems, but modern thinking is that it's not a good idea.

When you think about it, nothing else grounds that way. Everything in the vehicle grounds to the chassis. Wiring a radio to the battery negative creates a single alternate path.
I agree. You will NOT be able to create a lower impedance path than chassis ground. Separate negative lead to the battery neg is just another antenna to couple in noise. Same goes for winch ground for that matter - you will NOT create a lower impedance path with a dedicated wire. The reason for running a negative lead for a winch is the fact that its hard to create and maintain a reliable high current ground for one - and then the chassis connection can rust. I actually did both for my winch - ran the wire to the battery for reliability, and grounded to the chassis for lower impedance (I also had to beef up the negative battery to chassis connections). Best of both worlds, but for RF, omit the lead and keep the ground wire from radio to chassis as short as possible.
 
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Update: It's not happening today. Will have to wait until it happens again to test things, but in the meantime I suppose I can look for loose connections.

Ok, it started happening again today. Re-reading everyone's suggestions to try toubleshooting tomorrow.

Does the fact that this comes and goes given anyone ideas as to what I should try first?
 
Small cracks in the spark plug wires allow sparks to jump from the wire to any local ground. Large gaps on worn plugs make it much more likely the spark will form where it isn't supposed to. The cracks in the wires can be small enough you can't see them, that's why the water test in the dark is useful. You'll see the it light up as it arcs.

I'm back at this thread because the sound is back. I tried this tonight, but no luck.

If I think my spark plug wires are original, should I go ahead and replace them? Is that a likely source of interference?

Edit: Crutchfield seems to think so: "If your car is older and hasn't been tuned up recently, you may have ignition noise. It's a ticking noise that varies in speed as you accelerate. You may need a tune-up involving resistor-type spark plugs, shielded carbon-core spark plug wires, distributor cap, and coil."
 
Update: After changing my spark plugs and wires, I still have interference when the engine is running. I may just give up on chasing the cause and install something like what @WSS recommended in Post #2.
 
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I’m glad you asked. It’s directly to the battery, and your question reminds me that I should try an alternate ground spot to see if that fixes things.

Tie it to the tub as close as reasonably possible. Caveat: this may or may not fix the problem, but its a place to start.
 
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Our VHF radios are FM which is typically nearly immune to spark plug noise which is AM. How well is your antenna mount grounded? Can you post a good close-up photo of the mount and that shows everything from the cable to the bottom couple inches of the antenna? Have you done an SWR check as a sanity check to make sure there's not a problem with the mount or how well the antenna is tuned?

P.S. Connecting the radio's ground directly to the battery's negative post will cause ZERO problems.
 
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Our VHF radios are FM which is typically nearly immune to spark plug noise which is AM. How well is your antenna mount grounded? Can you post a good close-up photo of the mount and that shows everything from the cable to the bottom couple inches of the antenna? Have you done an SWR check as a sanity check to make sure there's not a problem with the mount or how well the antenna is tuned?

P.S. Connecting the radio's ground directly to the battery's negative post will cause ZERO problems.

Thanks Jerry.

Interesting point about AM vs FM. But I guess it was high time I tuned up those components anyway.

Antenna is well-grounded, and I can try to post some pics later today.

Have never done an SWR test on the Ham, but only on the CB. Can I use the same SWR meter that I used on my CB, or do I buy a different kind for Ham?
 
Thanks Jerry.

Interesting point about AM vs FM. But I guess it was high time I tuned up those components anyway.

Antenna is well-grounded, and I can try to post some pics later today.

Have never done an SWR test on the Ham, but only on the CB. Can I use the same SWR meter that I used on my CB, or do I buy a different kind for Ham?
The issue is that most inexpensive CB SWR meters aren't designed to handle the significantly higher power of most VFH rigs. But if you have a small low power handheld VHF radio that you can connect to your antenna you could use it instead of your main higher power radio. Or maybe your main VHF rig has a lower 5 watt or so power option?
 
The issue is that most inexpensive CB SWR meters aren't designed to handle the significantly higher power of most VFH rigs. But if you have a small low power handheld VHF radio that you can connect to your antenna you could use it instead of your main higher power radio. Or maybe your main VHF rig has a lower 5 watt or so power option?

Great to hear, thanks. Yes, I have a hand-held that I could set to 5W, which is about the same as my CB, right?

In the meantime, here are pics of my antenna ground. Although it's hard to tell in the pics, I can confirm that the ground strap is contacting bare metal, where I scraped the paint away with a wire wheel. Same is true on the underside of the antenna mount, where the coax comes up to the mount.

IMG_8039.jpeg

IMG_8042.jpeg
 
P.S. Connecting the radio's ground directly to the battery's negative post will cause ZERO problems.
Until it does. Usually, it won't. Sometimes, it can. I say connect it directly to the tub using as short a wire (or even braid) as possible. That too won't cause any problems - until it does. Grounding is black magic.