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Old 12-02-2021, 04:03 PM   #1
eccerr0r
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Default growing (not biological) rf noise from a car?

Just wondering, anyone have a car that seems to increase in rf noise generation over time, say, years...and what caused it?

I noticed my radios (of all types from hf to uhf) getting poorer and poorer as the squelch needs to be tightened to filter out the noise. Wondering if this is ignition or alternator noise, alas thinking alternator as I can't think of a proper way for ignition noise to get worse over time. Alternator is charging, however. Perhaps an omen to repair impending failure?
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Old 12-02-2021, 04:10 PM   #2
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Default Re: growing (not biological) rf noise from a car?

Grounding issues.
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Old 12-02-2021, 05:41 PM   #3
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Default Re: growing (not biological) rf noise from a car?

ignition is more of a ticking noise . alternator more of a whine both increasing with engine speed . disconnect antenna first to see if noise coming from there ,
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Old 12-02-2021, 07:02 PM   #4
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Default Re: growing (not biological) rf noise from a car?

Check to see if your alternator has a noise suppression capacitor on it if it does it probably not working correctly anymore if it does not have one add one but I can not tell you what value to start off with or use it is trial and error before you find the right value


Also have your alternator checked on a machine ( this is a special type of electrical testing equipment for alternators functionality tester ) [ one note not all shops have this type of machine you need to ask if the machine that they use can check the diodes in the alternator ] because you could have bad diodes in it but not bad enough that it discharging your battery yet but if this is what is wrong then give it enough time it will probably get worse if this is the problem ( When Sears was around I would tell you to take it there because they had that type of battery testing machine that could also check the alternator functionality test as well some Pep-boy service centers have this type of battery testing machine as well but you need to ask to make sure that this test can be done )

Now I have seen this before but I can not remember correctly the exact way to take two capacitors to make a non polarized capacitor and the use of a LED light and it will also tell you if your alternator has diode issues or not because I have a battery alternator tester machine and have repair it before and that was used and it does work ( if I can find where I have this machine I will take it apart again to see how this was done and post it here in this post ( but to do this test you have to turn all of your car electrical accessories ON to do this test correctly ) either it was both negative side of the capacitor was tied together or it was the positive side we’re tied together but if I remember correctly it does make a difference for this to work correctly

Now you can test this yourself however it not as accurate as the battery testing machine that I was talking about earlier but this is how you do this test

Now there is a more accurate test but it requires you to take the alternator apart and check the diode board or they are press fitted in the case of the alternator and use the diode function on a volt meter

Take you volt meter and use the ac voltage setting on the back of the alternator and see how much ac voltage you are getting if it is more than a volt you might have an issue with the alternator —> turn all of your car electrical accessories ON and also with them OFF to do this test correctly engine speed at 2000 rpm

Also check and see if the ignition coil or coil packs have a capacitor on it if it does then this could also be bad as well

One other note check and see if the alternator has a grounding cable that is attached to the back of the alternator if it does make sure that the connector is clean as well if not then check the grounding cable from the block to the frame of the car for clean connections

In a former life I was a battery technician that specialized in electrical troubleshoot electrical issues in cars and was ASE certified in this area

Way back when I use to rebuild alternators when the part were more available and less expensive than replacing a new one

I will still do this if an alternator is so expensive that it makes sense ( $150.00 or more) to do this but you need to be able to find the parts from the the junkyard for this to work but if this alternator has a built in voltage regulator it automatically gets replaced with a new one

I hope this helps you
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Old 12-02-2021, 07:18 PM   #5
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Default Re: growing (not biological) rf noise from a car?

yeah was thinking about putting a scope on the alternator output and seeing if there's any funny business going on there. Or maybe the regulator. I definitely hear some change in noise when I load down the electrical system but not that much.

An electromechanical connection issue is possible too. Sometimes I can get it to change when braking or accelerating, though braking also somewhat puts a load on the electrical system. Not sure where to start looking however.

This is a mid '90s car, though old now, it's not like a classic car that had RFI as an afterthought... that's why this is baffling.

Last edited by eccerr0r; 12-02-2021 at 07:21 PM..
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Old 12-02-2021, 07:37 PM   #6
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Default Re: growing (not biological) rf noise from a car?

had one recently where the owner complained about the noise .turned out to be a very cheap car radio . another thing in the old days there was a choke inline with the positive was in the fuse holder . i doubt its anything to do with it just saying like . any chance of a recording of the noise ?
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Old 12-02-2021, 08:33 PM   #7
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Default Re: growing (not biological) rf noise from a car?

I would start with the grounding cable connectors first then move on to alternator issues or maybe with ignition systems components there are several symptoms that noise issues can be caused by

Here is something to try take a wire that is long enough to go from the back of the alternator case to the negative terminal on the battery and see if you still have the noise or not

If the noise goes almost away you are going in the right direction compared to what you have now

One other thing to try is to hookup your radio directly to the battery terminals and see if this makes a difference or not as well

One other possibility is that the filtering capacitor inside the radio might not be doing its job correct anymore

One other possibility is that you might have a grounding loop issue I have my serious doubts about this being the issue however in some stereo system had issues with picking up noise from the alternator charging system and they sold a device that if I remember correctly it had choke coils in it to remove the noise and I have even used them myself and they seem to work stereo system to power amp setup

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Old 12-02-2021, 08:47 PM   #8
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Default Re: growing (not biological) rf noise from a car?

Well it's clear it's not power distributed noise actually, it's being radiated into the air as battery and isolated receivers pick up. Also have multiple radios that are "hearing" the noise.
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Old 12-02-2021, 09:00 PM   #9
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Default Re: growing (not biological) rf noise from a car?

How far away are you picking up this noise from the car and is the noise a whiny and changing pitch with electrical load or engine speed more like a from the ignition noise coming from distributor cap

Because car from that era would keep running even if the distributor cap was bad up to the point just before the carbon track would ground it out and then would make the engine not run anymore

New car will not allow it to get to this point

Think about this it also possible that you might have ignition spark plug wires could also cause noise issues as well

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Old 12-02-2021, 09:44 PM   #10
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Default Re: growing (not biological) rf noise from a car?

hmm... guess i'll have to pull the cap and see if there's anything going on in there.
Newer cars don't have a rotor or cap... :o

Wonder if some day I'd need to convert the engine to be COP similar to people converting from points to electronic ignition...
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Old 12-03-2021, 07:48 AM   #11
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Default Re: growing (not biological) rf noise from a car?

Quote:
Originally Posted by eccerr0r View Post
hmm... guess i'll have to pull the cap and see if there's anything going on in there.
Newer cars don't have a rotor or cap... :o
I was referring to cars just before they went to coil packs and did away with distributor cap and rotor there was a brief time that had electronic ignition modules
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Old 12-03-2021, 01:49 PM   #12
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Default Re: growing (not biological) rf noise from a car?

check the ground strap between the engine and body - remove it to check the contacting surfaces.
if you put disimilar metals together - such as aluminium and steel/zinc you get galvanic corrosion.
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Old 12-03-2021, 02:53 PM   #13
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Default Re: growing (not biological) rf noise from a car?

walk around the car with a radio and see where the noise gets the worst
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Old 12-03-2021, 09:35 PM   #14
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Default Re: growing (not biological) rf noise from a car?

As far as I can tell there's two wires leading off the battery negative terminal, one to body and one to engine block. I suspect the one to the engine block must be ok else starting would be a problem. The other connection looks clean, not loose, no rust, never gets wet... hmm. now that's to the frame, not sure about connectivity to hood, etc. yet.

Still have not pulled dist cap off to inspect though I think it's been ~60K miles since last replacement, though I think I replaced it then, I don't remember ...
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