Alternator noise problem

[Punkin Head]

I am wondering what else I need to do to get rid of the Alternator noise in the radio. I have it grounded to the frame, power wire hooked to the battery, antenna grounded to frame. I guess I will need to start adding ferrite beads to power wires maybe?

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[dirtyjob]

perhaps change your plug wires to some thick 8mm ones for better supression ?

perhaps this link will help also:

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[Punkin Head]

perhaps change your plug wires to some thick 8mm ones for better shielding ?

I will try that. Its due for a tune up anyway. We will see how that works out.

[Slyguy]

Yeah that's not alternator noise. that's ignition. I don't know the year model of your bronco but I bet a cap and rotor will do wonders.

[Punkin Head]

Yeah that's not alternator noise. that's ignition. I don't know the year model of your bronco but I bet a cap and rotor will do wonders.

1993 Bronco XL with 351w fuel injected. Gonna do a full tune up and replace all that good stuff with better parts and see what it does. Hope it fixes it. As of now I cant hear anybody with truck running, have to turn it off to talk and crank it up to recharge battery.

[MDYoungblood]

Hey PH,
This was posted on another site but it does work, several of the members including me have built it.

I recently installed a new transceiver in my truck. On the first day of using the new radio I got reports that I was transmitting very noticeable alternator whine. I could also hear it on receive and when the radio was quiet. I checked the diodes in the alternator, verified I had good grounds, and I even ran the truck with the alternator removed to be sure that the whine was indeed from the alternator.

The alternator produces AC, which is rectified into DC. The problem is the rectification is not perfect. The DC output will have a small AC signal riding on it. That AC signal will have 9 cycles for each revolution of the alternator. Suppose your engine is idling at 600 RPM and the drive pulley ratio to your alternator is 1:3. At that engine speed your alternator is turning 1800 RPM, which is 30 rotations per second. Each rotation gives you 9 cycles of AC. Do the math and you get a 270 Hz sinusoid (not a perfect sinusoid but close enough). Cruise down the road at 2000 RPM and you get a 900 Hz sinusoid riding on your DC power supply.

I tried an off the shelf filter from Advance Auto. It did very little so I decided to build a filter. The first filter I built worked VERY well. The problem is that not everyone has the tools required to build that filter so I decided to figure out a filter design that could be built in less than an hour by anyone with basic tools, have a cost under $20, and handle a current of at least 20 Amps.

Parts List:
1/2" Quick Link from Lowe's $2.98
6x3x2" project box from Radio Shack $3.79
20' roll 12 gauge red hook up wire from Radio Shack $4.99
4700 uF 35V capacitor from Radio Shack $5.29
18" of black 16 gauge wire
electrical tape
GOOP or similar glue
3 zip ties
Total: $17.05

Directions below
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1/2" Quick Link will be used as the inductor core. A fellow
ham, Dave KC1LT, suggested using a shackle. I went to get
a shackle and came across this quick link. I went with the
quick link to make more efficient use of project box space.
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Beginning the winding
Wrap the hook up wire around the closed side of the quick link starting
from the left as shown. Leave about 9" of wire free on the left end. Try
to keep the winds as close together and tight as possible. On the last layer
space the winds so that you have 9" of wire left on the right end. Use all 20' of wire.
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Above is the finished wrap
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Wrap the coils in electrical tape and close the quick link. About 1.5" from the right
end of the inductor strip 1/4" of insulation off the red wire and solder in the + lead
of the capacitor. Make sure you observe the capacitor polarity. In the picture you
can see the negative arrow on the capacitor pointing down. Solder the 18" piece of
black wire to the negative lead of the capacitor. (Above)
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Cover the solder connections and capacitor leads with electrical tape.
Drill a 3/16" hole in both ends of the project box for the red wires. Drill
an 1/8" hole in one end of the project box for the black wire. Run the
wires through the holes. Put a zip tie on each of the three wires to limit
how far the wires can be pulled out of the box. Make sure to leave a little
slack in the wires inside the box. Using GOOP or some other thick strong
adhesive, glue the capacitor and inductor into the project box. Leave the
cover off until the glue dries.
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+12V Side with the capacitor to radio
Black Ground +12V to battery
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Measured Filter Response:
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I made this measurement using a low frequency signal generator and an oscilloscope. At 25 Hz the filter has better than 30 dB of attenuation. In other words for frequencies above 25 Hz the noise power has been knocked down by more than a factor of 1000.
I am new to practical electronics. By answering basic questions and making suggestions several folks contributed to this. In particular Dave KC1LT was very helpful. I hope this information is useful. If you use this design to build a filter or if the information presented was useful please send an email to kb1mvx@comcast.net and let me know it was worth the effort to put this together.

73

Greg

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Sun Jan 13, 2013 7:40 pm

Just played the YouTube, defiantly needs a tuneup, I can hear your Bronco idling in my radio over here, lol.

3's

Greg

[Punkin Head]

I will try that filter out too MD. Thanks for that info!

Also, I have an MSD Distributor and 8mm MSD plug wires in the Bronco. Would the MSD cause more interference with the radio than the stock distributor would?

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Sun 13 Jan, 2013 22:04 PM

May add one of these to the list of things to try too. Hopefully I can get this noise under control.

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[231]

I would be interested in hearing how bad the noise is with the NB/ANL on.

[Chief_River]

I would be interested in hearing how bad the noise is with the NB/ANL on.

That's what I was going to suggest. I just installed my Cobra 29LTD Classic in my 2002 Chevy Tahoe, and when I started it up had a considerable amount of ignition noise. I flipped on the ANL, and without having to go further to NB/ANL, it filtered the ignition noise out completely.

I know the OP states 'alternator noise', but I'm assuming he meant 'ignitioin' also. I've never heard 'alternator noise' in a mobile radio.

[420Snowman]

I will try that filter out too MD. Thanks for that info!

Also, I have an MSD Distributor and 8mm MSD plug wires in the Bronco. Would the MSD cause more interference with the radio than the stock distributor would?

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Sun 13 Jan, 2013 22:04 PM

May add one of these to the list of things to try too. Hopefully I can get this noise under control.

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MSD ignition systems have a "hotter" setup and may cause some noise. Make sure your coil is grounded very well and your power wire for the radio is as far away from the distributor as possible.


Snowman

[Punkin Head]

I would be interested in hearing how bad the noise is with the NB/ANL on.

its about the same, I will do a vid showing that in the next day or two.

[721HACKSAW]

Is the noise getting in the radio through the DC power or through the antenna? When removing the coax does it change? Alternators and electric fuel pumps are the biggest culprits.
Good luck and enjoy.

[Punkin Head]

Is the noise getting in the radio through the DC power or through the antenna? When removing the coax does it change? Alternators and electric fuel pumps are the biggest culprits.
Good luck and enjoy.

I will unhook the coax this weekend when I mess with it again and check. I am thinking its coming in thru the wiring but I could be proven wrong. Will post results.

[alhefner]

I have about the same sounding noise. It's coming through the antenna. When I unhook the coax, all is silent. Mine is a 1990 Bronco and I'm betting I need to do a tune...or at least a cap and rotor...

[Radar-DLDN]

I built that exact filter that MDY posted. As far as I can tell it works great. Problem is that it proved that I didn't check if the noise was coming from the antenna system, which it was and still is. So make sure you check that before you build the filter. Not that it's expensive or difficult to build, but if it's your antenna it won't fix your problem.

[dirtyjob]

another thing to consider is many vehicles today have separate fuel injectors and spark coils for each cylinder, this can create pulses on the vehicles wiring and since a car/trucks exhaust system is bolted directly to the engine and suspended by insulated mounts it can act like an antenna and radiate these pulses, thus being picked up by your antenna, grounding your exhaust will help counter this. I just read about this in dx engineering magazine and they do sell exhaust grounding kits specifically for this issue.

[Punkin Head]

I havent done anything else to it yet. But I have lots of things to try thanks to this thread. Just waiting on warmer weather. I will be sure to update this more when I do get to trying the different solutions and post up what worked. Thanks again to everyone and keep the ideas coming