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Author Topic: Correcting Alternator Whine  (Read 15664 times)
KG5HZT
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« on: June 30, 2015, 10:13:26 AM »

The setup: Yaesu FT-60R using a Diamond MR77SMA antenna on my vehicle.

I was monitoring the local repeaters the other night and noticed a buzzing coming through the HT.  The car was running, as it was a warm night here in South Louisiana, so the A/C was rolling.  I shut the car off and the buzz went away.  I'm assuming that the feed line is picking up the car's alternator.  I want to install a clamp on ferrite choke on the feed line near the SMA connection to the HT, but I have a question regarding matching the impedance of the choke and the feed line.  Does the impedance have to match, e.g. 50 Ohm choke for a 50 Ohm line, or should it be less? Or more?

Thanks for any assistance in advance.

Doug KG5HZT
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K5LXP
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« Reply #1 on: July 01, 2015, 07:04:46 AM »


Is there a DC connection from the radio to the vehicle, or just an antenna?

If it was the alternator, the DC path would be the one to fix.  If it's through the antenna only, there's nothing an alternator puts out you'd be picking up on VHF or UHF.  Rather it's a CPU, injectors, or one of a myriad of widgets that run while a car is running.  You can try and isolate the subsystem by turning things on and off but without going to extremes to shield and isolate any offenders, the first order mediation will be to bond all the panels, doors, exhaust and driveline together.  That can buy you a few S-unit reduction and should be done as a matter of standard practice for mobile installations.


Mark K5LXP
Albuquerque, NM
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KG5HZT
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« Reply #2 on: July 01, 2015, 07:59:03 AM »

Mark,

It is just the antenna, as the HT is running solely on battery power.  Thinking about what you've said, I think I might be picking up something from the CPU.  Right now I have the feed line snaked down the windshield trim, then into the left quarter panel and through the door, so it's more than likely that it's getting interference from something around there.  I think I'm going to try to move the feed line and see if that clears it up.  Thanks for the help. 73.

Doug
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N9BH
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« Reply #3 on: July 02, 2015, 05:15:57 AM »

Do you have the problem when using a rubber duck antenna?
Do you have it on all frequencies?
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KG5HZT
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« Reply #4 on: July 02, 2015, 03:06:05 PM »

Do you have the problem when using a rubber duck antenna?
Do you have it on all frequencies?

No on the duck antenna, and yes it seems to be on all frequencies.   I've isolated it to the engine, as it does do away when I shut the engine off, probably the injectors. How can I isolate that and get rid of it.

Doug
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KD0REQ
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« Reply #5 on: July 02, 2015, 06:09:57 PM »

before you start working on it, fire up the radio with the ignition off, and then turn the key to RUN.  if your buzz comes back and then stops, the fuel pump is the culprit.  you can't get to it directly without dropping the fuel tank (multiple dangers exist here.)  you might get lucky clipping a few ferrites on the power line to the fuel tank (it that's not within frame members or a siamese line on the fuel hoses) with an insulator on the tank side, and slide it up as far as you can before fixing the position with cable ties.

I had a Ranger 1990 that was wild with pump noise.  found that out at the edge of the BWCAW, no options.  the RS franchise store had the usual few caps, and I knocked it down enough to be borderline useable with a 5000 uF and a .001 across the pump feed power under the drivers' door.
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KG5HZT
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« Reply #6 on: July 02, 2015, 06:26:04 PM »

before you start working on it, fire up the radio with the ignition off, and then turn the key to RUN.  if your buzz comes back and then stops, the fuel pump is the culprit.  you can't get to it directly without dropping the fuel tank (multiple dangers exist here.)  you might get lucky clipping a few ferrites on the power line to the fuel tank (it that's not within frame members or a siamese line on the fuel hoses) with an insulator on the tank side, and slide it up as far as you can before fixing the position with cable ties.

I had a Ranger 1990 that was wild with pump noise.  found that out at the edge of the BWCAW, no options.  the RS franchise store had the usual few caps, and I knocked it down enough to be borderline useable with a 5000 uF and a .001 across the pump feed power under the drivers' door.

It'll definitely check that out.   Thanks.
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AA4HA
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« Reply #7 on: July 06, 2015, 08:40:15 AM »

before you start working on it, fire up the radio with the ignition off, and then turn the key to RUN.  if your buzz comes back and then stops, the fuel pump is the culprit.  you can't get to it directly without dropping the fuel tank (multiple dangers exist here.)  you might get lucky clipping a few ferrites on the power line to the fuel tank (it that's not within frame members or a siamese line on the fuel hoses) with an insulator on the tank side, and slide it up as far as you can before fixing the position with cable ties.

I ran the fuel hoses through ferrites. Since the car is gasoline powered I figured that if I started with RFI-free fuel then the entire car would be electrically quieter.  Wink
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
KG5HZT
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« Reply #8 on: July 09, 2015, 07:03:21 AM »

Here's another thought I had, would a high pass or band pass filter help? 
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K5LXP
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« Reply #9 on: July 10, 2015, 07:34:52 AM »

Here's another thought I had, would a high pass or band pass filter help? 

No.

Mark K5LXP
Albuquerque, NM
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KD0REQ
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« Reply #10 on: July 10, 2015, 09:53:20 AM »

AA4HA, that only reduces unwanted RF in the exhaust.  all other emissions stay the same.  since that is by definition part of the air, not the luminiferous aether we throw our CQs into, probably won't help.

but it was worth a chuckle.  as was my truck after 10 years....
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KC2MMI
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« Reply #11 on: July 19, 2015, 04:31:48 PM »

There are "alternator noise filters" sold, any car stereo shop will have them and the $15-20 ones will do well enough. BUT. That noise many indicate the alternator brushes are worn, or there's a bad ground, or a bad electric component in the alternator. Try contacting the car's maker or the alternator maker for specifics to your alternator and car and see if you can fix the problem, rather than masking it. (While it gets worse until something fails.)
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K1DA
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« Reply #12 on: August 08, 2015, 04:27:20 PM »

Alternators usually whine, not buzz, and the frequency changes with engine RPM.  Be nice to take us out of the dark and tell us what kind of car it  is.  Sometimes googling the make,  model and problem will do wonders.
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KG5HZT
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« Reply #13 on: August 08, 2015, 04:34:22 PM »

Alternators usually whine, not buzz, and the frequency changes with engine RPM.  Be nice to take us out of the dark and tell us what kind of car it  is.  Sometimes googling the make,  model and problem will do wonders.

It's a 2005 Mazda Tribune, and it does change with the engine, but it doesn't happen all the time and on every frequency.

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KD8IIC
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« Reply #14 on: August 08, 2015, 08:42:06 PM »

You gave two clues that will help narrow it down.
(1) you're using an HT and I assume you tried it on its' own battery power or do you have it hooked to the cig lighter, which one?
(2) You also state the A/C was in use, it is possible you're hearing the Heater/AC blower brushes and commutator noise.
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