Well ive been fighting a whine in my CB for a while now. I replaced my Cobra with a new Galaxy and the whine is quite a bit louder out of my external speaker. I already disconnected the antenna lead to the radio to rule out antenna picking up interference. Radio still made the noise.

How ever I did the little test I read online switching multimeter to AC current and with engine running check at battery should be less than 1.5V AC. I had 00.001V AC. So there is no bad rectifier based off that test I found online. I checked voltage 13.33 volts at idle so the alternator is charging.

I turned my AM/FM radio down and started the truck up and could hear a faint whine. I flipped CB on and the whine was louder that I had two radios putting out. I also for a while now noticed a whine outside of the truck sounding like its coming up through the floor board.

I started thinking and I am wondering if my 1G alternator (which I don't know when it was last replaced if we ever even replaced it) is going bad internally and is introducing this whine.

Wished there was a simple way with a multimeter to test the alternator to verify something is failing inside causing this electrical noise. I sure hate to spend money I don't have on an alternator and it doesn't fix my whine.

 

Single wire, ground mount resistor found at most parts outlets.

 

You know those little mystery silver round cans here and there with a single wire coming out of them that the factory installed? You see them at the regulator, sometimes on the back of the alternator, etc. That's what they are for. Capacitors do not pass DC, but they do pass AC current. The whine is a high frequency AC current riding on your DC supply. These little metal capacitors will conduct this to ground and get rid of it.

If you still have problems, you can go to the stereo shop and get a choke coil. They probably call them noise suppressors. They are not cheap, and can only handle a certain amount of power through them, but they will get the last bit out. They are a coil. Coils are opposite capacitors, coils don't conduct AC, they do conduct DC. So the coil is hooked inline to your radios. The DC current flows through, the AC is blocked. This along with the capacitors should clean it up.

 

Is there a way to check the capacitor at the regulator? I unplugged it seemed like the whine in my AM/FM radio got a little louder. Plugged back in it went a little quieter but my CB is still loud as hell.

I wonder if I should just try replacing this capacitor at my regulator it says motorcraft on the back of it just like my regulator so its never been replaced since we had the truck.

 

It's probably ok. I would add some more, one directly on the back of the alternator. Put the wire right on the large stud on the alternator.

You may end up getting a choke to get rid of all the noise. Here's one from Amazon.

 

Ive been looking at Ferrite style noise filters down to regular old CB/Radio noise filters.

I'm just not sure if I should try to add a filter on the main power wire for the auxiliary fuse box I mounted under the hood or just add a filter on my CB circuit itself coming off the fuse box.

 

Put the toroidal choke as close to the CB as possible.
This removes the power wire as an inductor or antenna.

Kr would love you to participate in his little alternator ripple cult.

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how big are the Toroidal chokes? cause I keep looking at these CB/Radio filters that I think are basically toroidal chokes internally but I don't have any place to really mount behind the dash as I am running out of space with everything I have mounted behind the dash.

 

There's nothing keeping you from installing a condenser at your junction block *and* a choke/filter/inductor on the power lead at the back of the radio itself.
Both serve the same purpose but work in different ways.
As Dave said, the condenser will pass AC~ back to ground while isolating DC.
​​​​​​​A choke blocks AC and allows DC to pass.
A simple ferrite bead *may* be effective. Or maybe you are better off with wirewound, Idk.
It would help to know whether your interference is radio frequency - that is showing up because of the amplifiers in the radio- or audio frequency.
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I guess you'd need to scope it to know for sure.
(maybe kr knows what an alternator averages)
I would assume 3x alternator rpm.

Can you be certain this is alternator ripple and not EMI from your ignition?
Is there a condenser on your coil?
Do you have radio suppression plug wires with resistor caps or resistor plugs?

Beyond that you are going to have to make a Faraday cage for the radio itself....

 

This may not be a valid test. Even with the coax disconnected, the receiver is still trying to amplify whatever it senses, whether it comes from the antenna or free air. With everything hooked up as normal, and the whine present, try holding your hand on the antenna. See if that helps. That should help isolate if you've got a dirty DC power supply (no change) or an antenna issue (less whine).

Read through these articles and see if you think a faulty antenna ground path could be part of the issue:

How to Ground a CB Antenna


https://www.rightchannelradios.com/b...g-for-a-ground

I'm drawing a blank whether a bad ground can cause a whine, but it's quick and easy to rule out.

Okay, fine, I'm in. Try the AC ripple test right at the alternator, not the battery. You wouldn't think it would make any difference, but it can. Put the (+) lead on the big insulated alternator terminal. Put the (-) lead directly on the alternator case. Try different speeds, not just idle.

Also be aware the AC ripple test is not conclusive. If it fails, yep, that's a failed diode(s). If it "passes", it could just mean your meter can't catch the spikes. An oscilloscope is the only way to be sure. Some meters can give a reasonable approximation, but not all.

With the whine present, try adding heavy electric loads such as the heater fan and high beams. The extra load helps absorb any AC spikes. That can help confirm the presence of AC spikes your meter can't see. Repeat the AC ripple test and see if there is any change in the reading.

Is the whine RPM-dependent? Several sources I saw suggested this could be caused by the ignition, not the alternator. A marginal ground between the engine block and frame can cause trouble. Try adding a test jumper there and see if that helps.

 

the whine doesn't change from channel to channel its the same through all channels.

I don't know if its from the ignition but I have Ford Racing spark plug wires which are carbon core not solid core. I don't know if there is another condenser/capacitor at the coil I want to say there is one bolted on the coil mount bracket but I cant say for sure off the top of my head.

If I mount a condenser/capacitor onto the core support for ground and the wire to the positive terminal on the fuse box there shouldn't be any issues with this being straight battery voltage? I don't see why there would be but just curious.

 

It is rpm dependent. As you drive the whine goes up and down based off engine rpm. Sounds like traditional alternator noise that you see mentioned in old shop manuals.

If its ignition related is there some way to find out? like a jumper wire or something? I thought of running a jumper wire from the cab to the engine block to see if that helps but I don't know what I will be able to achieve tomorrow as I have some plans around noon.

 

Ding, ding, ding, ding, ding!

Given the chance to spend your time and money, I'd lose the racing wires. I should clarify you'll need to install something else, as performance will suffer if running without any plug wires at all. Probably hard to start, too.

No guarantees of a fix, but racing plug wires are gonna put out a LOT more ignition noise than regular plug wires.

 

well I don't think theses are racing wires, they are just made by Ford Racing. They were the only plug wires I found made by Ford/Motorcraft that is made for the engine that is the right length.

I did read this just now.

https://www.installdr.com/TechDocs/999501.pdf

I am thinking of disconnecting my ground wire for the CB and using a jumper wire and connect it directly to the negative on the battery to see if the noise goes away. I cant remember if I moved the ground or not but I got something like 4 or 5 ground wires bolted to the metal dash frame via two screws. Might be one too many ground wires on one screw for the radio. But I cant remember I did my original install last year and I had this problem then just lived with it as it wasn't that loud. Now this new radio is loud as hell when I installed it today.

these are the wires here they say they have RFI suppression.
https://www.summitracing.com/parts/f...view/make/ford



Only thing on my mind right now on the capacitors is I cant find nothing like the oem ford ones I have on my voltage regulator. I wonder if the ignition capacitor that I can find easily would do the same job if I were to mount it to the core support and mount the single wire to the battery terminal on my fuse box.

 

Don't overlook that you have the primary side of the ignition in the wiring bundle under the dash - assuming you have gauges and not idiot lights. It comes in for the tach, and due to the fairly significant EMI on it there could be some induced ripple on other wires.