Alternator noise suppression

[remingtonh]

I thought of that. Every 3-4 years, I have a capable mechanic do a bumper-to-bumper inspection and fix everything that needs fixing. It's due for that this summer. I'll specifically mention the alternator and if it's even borderline, I'll have it replaced.

I never put the cheap crap on my truck. That's why it's immaculate despite its age.

(No cracks about the radio being "cheap crap". I knew it was entry-level when I bought it. I wasn't sure how much I'd get into ham radio, so I didn't spend the big bucks. It's working just fine and doing everything I want. If/when it craps out, I'll replace it with something high-end. If it doesn't crap out, then there was never a need for something else anyway. Besides, the radio isn't a permanent part of the truck.)

Your capable mechanic, as skilled as he may be mechanically, likely knows little about RFI mitigation.

 

[OkieBoyKJ5JFG]

Your capable mechanic, as skilled as he may be mechanically, likely knows little about RFI mitigation.

Almost certainly not, but if there's a question about the alternator, it's only logical to start there rather than chasing a bunch of other stuff only to find out that the alternator is failing.

 

[slowmover]

I'm not going to resort to a new alternator unless this one is failing or nothing else works, but I'll keep that in mind. Hopefully, changing my grounding location will fix the problem.

DODGE Transceiver Installation Guide will tell you to connect the unfused NEG to the BATT Neg fender connection bolt. (Remove paint).

I can use the Cigar Lighter power cord with my Lincoln II+ and hear the alternator (136A Denso) in my ‘04 2500 CTD. That’s not a surprise.

CORNELL-DUBILIER for Alternator noise control products after a KLF-2 is tried.

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[k6cpo]

When I installed the first radio in my then 13-year old Dodge Dakota, there was a little alternator noise heard in the radio's audio itself. I installed one of these filters in the power lead close to the radio. It's been through five different radios in the same vehicle and it's still quiet.

 

[TGuelker]

Another possibility is the electric fuel pump. The noise will change with rpm because the alternator is increasing the voltage to the pump. One way to test is to energize the fuel pump relay and transmit. An oscilloscope on the pump feed and ground should produce 7 or 8 smooth humps with no noise depending on the pump manufacturer. DENSO pumps will not have a waveform because they are brushless.

 

[AC9KH]

On a 16-year-old vehicle, I'd question the health of the alternator. If you can identify the alternator as the source (pitch of the noise rising and falling with engine speed), I'd consider replacing the alternator. No, it won't be cheap and, no, they don't make 'em like they used to. If you do replace the 'nator, get a name brand one and not a cheapie.

How about just fixing the alternator instead of replacing it? It's a simple three-phase AC generator with a bridge rectifier on each phase. If it's putting noise into the DC system then it has a leaky diode. No need to replace a perfectly good alternator because of a bad diode.

 

[AK9R]

Yes, repairing is an option if it's available to you. Assuming the alternator is repairable by the average home mechanic or you can find an automotive electrical shop that can repair it for a fair price in a reasonable time frame.

 

[OkieBoyKJ5JFG]

UPDATE: I'm really baffled now.

So...I moved the negative ground close to the radio and had the alternator checked, but I have used the radio very little since I last posted in this thread, and I had other things going on, so I never checked into it any further. Tonight I knew I was going to be using it while driving so I decided to isolate the source, if possible. First, I tried it with the engine off. No noise (unsurprisingly). Then I tried it while driving and I got a whine/white noise that went up and down with the engine RPMs. Then, just for good measure, I put the radio on a LiFePO4 battery, and to my surprise, I still get the whine when the engine is running. I assume it has to be some sort of RF interference generated by the engine but unrelated to the wiring. Any ideas?

I used it tonight while driving to a football game crossbanding UHF from my truck to my home radio crossband to the VHF repeater and was told I had "very little" white noise, but nothing was said about a whine. I don't know it wasn't there, or if the other operator just didn't mention it. Driving back and talking directly to a UHF repeater was when I was told it was happening, even on the LiFePO4 battery. I haven't tried it with a different radio yet, which is my next step, but even if it doesn't happen with another radio, I'd like to know what's going on. I also haven't specifically checked to see if it's occurring on both UHF (like tonight) and VHF, but IIRC, a few months ago, I was on VHF when someone reported it to me. Can it somehow be affected by what antenna I use? That's easy to swap as well and I can certainly try it. Any ideas are welcome.

 

[mmckenna]

Couple of things:

How do you you know you are transmitting with a whine? Are others reporting that, or are you hearing it on a hand held radio in the vicinity of the truck?

If you've taken all the steps recommended so far and it's still there, then there might be something else going on.
Routing of the positive power from the battery may run too close to something that is carrying or generating the noise.
Same with the coax. Some coax has poor shielding, so maybe the coax is run too close to something. I think this is a mag mount, so maybe rerouting the cable/mount away from the truck and see if that helps.

Remind me what kind of truck it is? Some vehicles are just noisy.

 

[chief21]

I put the radio on a LiFePO4 battery, and to my surprise, I still get the whine when the engine is running. I assume it has to be some sort of RF interference generated by the engine but unrelated to the wiring. Any ideas?

Disconnecting the antenna while the radio is on and the engine is running might tell you whether the noise is coming in on the DC feed or the antenna line.

 

[Chris155]

I’d try engine running alternator unplugged. You can disconnect small signal wire only and it will effectively turn the alternator off. I had 2 noisy replacement alternators on my current truck, they checked out fine but made lots of noise in my cb. Finally got a new denso alternator, nice and quiet.

 

[OkieBoyKJ5JFG]

How do you you know you are transmitting with a whine? Are others reporting that, or are you hearing it on a hand held radio in the vicinity of the truck?

It's being reported by people on the other end. Last night, it was reported when I went directly to a UHF repeater. It wasn't reported earlier when I went UHF-to-VHF crossband through the radio at my home, although the other operator did report "a little white noise". I don't know if the whine wasn't there or if the other operator just didn't mention it.

Routing of the positive power from the battery may run too close to something that is carrying or generating the noise.
Same with the coax. Some coax has poor shielding, so maybe the coax is run too close to something. I think this is a mag mount, so maybe rerouting the cable/mount away from the truck and see if that helps.

I don't think the positive power is the problem because the whine was still there when I completely disconnected from the vehicle power and ran the radio on a LiFePO4 battery. On the battery, the whine was only present when the truck was running, just like when it was connected to the vehicle power.

The coax runs from an NMO mount in the driver-side rear stake pocket under the bed rail, down to the floor of the cab, and up through the drain hole to the radio under the driver-side seat, so I don't think the coax is close to anything electrical except perhaps the taillight. The coax itself is 15' of RG8X. I could try using a mag mount antenna on the roof to see if anything changes.

Remind me what kind of truck it is? Some vehicles are just noisy.

It's a 2009 Ram 1500.

 

[OkieBoyKJ5JFG]

Disconnecting the antenna while the radio is on and the engine is running might tell you whether the noise is coming in on the DC feed or the antenna line.

The noise is only present when I transmit; I don't hear it on my end. I don't think it's coming from the DC feed because it was still present when I ran the radio on a separate battery.

 

[OkieBoyKJ5JFG]

I’d try engine running alternator unplugged. You can disconnect small signal wire only and it will effectively turn the alternator off. I had 2 noisy replacement alternators on my current truck, they checked out fine but made lots of noise in my cb. Finally got a new denso alternator, nice and quiet.

That's easy enough that it's certainly worth a try. Could the alternator be the source of the noise even though the radio is not connected to the vehicle's electrical system? It's still present when I power the radio from a separate battery with the engine running.

 

[buddrousa]

The antenna system is still connected to the chassis and stray rf can come from anywhere. Just look here on the forums and you will see post about new cars for law enforcement having interference from the computers that run the car.

 

[OkieBoyKJ5JFG]

The antenna system is still connected to the chassis and stray rf can come from anywhere. Just look here on the forums and you will see post about new cars for law enforcement having interference from the computers that run the car.

Hmm. Would it tell me anything useful if I put the radio on a mag mount antenna; i.e., not connected to the chassis? And if it turns out that's the case, what can I do about it?

 

[buddrousa]

I would say if you know someone with an oscilloscope and you connect it to the 12 volts of the car you would see AC on the 12 volts that comes from the alternator where it is not getting filtered.

 

[buddrousa]

 

[OkieBoyKJ5JFG]

I would say if you know someone with an oscilloscope and you connect it to the 12 volts of the car you would see AC on the 12 volts that comes from the alternator where it is not getting filtered.

I don't know if you saw it, but the whine still occurs when I'm running the radio from a separate battery, not connected to the car's power system. Would this still apply?

 

[mmckenna]

So, it sounds like radiated RF noise from the ignition or alternator. Maybe.

It doing it on some bands and not othes is curious. If it's not doing it when you are cross banding, then there may be some filtering in the radio that's catching that noise.

Like i said, some vehicles are noisy and some of this may just need to be something you live with. Dodge trucks have their share of complaints, and you are certainly not the first to report RF noise. A magnetic mount antenna moved around to varioius places on the vehicle might be something to try. Usually with RFI, the solution is to move the radio/antenna away from the source.