First what is Alternator noise or Alternator whine or buzzing when you speed up and slow down..
Back in the 50 car used to have generators that made DV voltage sometime in the 60s they switched to Alternators that produce AC voltage.
The AC voltage in converted to DC by diodes and then kept at the proper dv voltage by a regulator. In modern cars this is all built inside the alternator. The battery is charged by this voltage and the battory acts like a large capacitor to straighten out the signal. When you get a whine what you are hearing is called Ripple. Ripple is ac voltage riding on top of the DV voltage.
In the above example the 12 volts is present but its not a straight line it has ac in it. It could also have different types of spikes other unregulated voltage.
The sound in the radio will change as you speed up or slow down because the speed of the alternator is changing changing the frequency of the AC. A good technician can hear the ripple over the air because of the change of the frequency of the sound, nothing else does this.
So me people will tell you need to ground. Some will tell you to run straight to the battery. But they don’t know why. To understand how to fix alternator whine on GMRS you need understand what it is.
- Its AC voltage or spikes riding on top of the DC.
- Simple power supply theory taught in the 70s before IC power supplies.
In order to get rid of ripple you must remove the AC using a cap and a choke. They sell 12v noise filters for car audio that will remove this and there is no need to run heavy wires to the battery. .
When looking for a noise filter be sure it has 2 caps one on each side of the coil. Get the largest MFD value for the cap you can find. I make my own but I have lots of caps.
This is called a PI filter this circuit flattens out the dv voltage removing the ripple.
There do exist 12v noise filters with only one cap but I would not recommend them.
But you say what about running direct to the battery. When you do that the battery is acting as a cap partly flatting out the ac. However if the ripple is large then the battery cant fix it. So it is not necessary to run to the battery all you need to do is use a pi filter to remove the ripple at the radio.
But what about torids they say just put torids on it. A torid is an inductor just like a coil. The inductor blocks AC but the CAP stores voltage and releases in the the low point of the ac signal leveling out the voltage. A torid cant do that. You need both to filter out AC.
SO don’t waste your money it will cost less just to use a filter than to buy the wire to run to the battery and the battery can only do minor filtering so it still may not work.
But someone said that I should install .01 cap the radio. This is for something totally different. Old cars used to have a cap like this in many places under the hood to help stop noise from getting into lines from the points and such. The value is to small to stop RIPPLE loud enough for you to hear.