Hello Big Nasty Trucker:
The "Snifer" technique is a hands on way of isolating the noise, and will take some pratice to master.
Using the coax and the radio to sniff the noise can be done but needs some explanation to use it. And you do "NOT" want to transmit with the sniffer coax attached to the radio.
Suggest you hook up a length of coax as Moleculo suggested. A length of coax that is connected to the radio antenna connector. and the other end can be wired two ways, for two functions.
Having the center wire exposed, say a inch or 1/2 inch will allow some energy to picked up by the radio. This will allow you to find the noise sorce in its general location.
Remember the radio is designed to hear RF signals in the 26 to 28 Mhz range, depending on the radio, but the cheaper radios will also allow audio frequency signals in thru the receiver so you will hear noise and signals not in the RF Range of frequencies. But still the radio can be used a great sniffer, especially if it has a RF Gain that can be turned down to allow you have a not so hot receiver which is what it takes sometimes to isolate and identify the noise sorce.
I have used a small Transistor AM/FM Radio to look for noise under the hood of a few vehicles, all I could tell was yeah there was noise coming from under the hood but could not tell where it was coming from because the little Transistor (8 dollar Radio Shack Radio) was too darn sensitive. It was depositied into Mr Trash can, the same place I put Gamma Matches....... BTW
With the ability to reduce the sensitivity of the receiver with the RF Gain control, and the sniffer coax, while listening to the speaker, is a major neat O thing in isolating where the noise is coming from.
The sniffer coax can even have the center wire having a 1/2 inch exposed loop, soldered to the shield. Again not for trasmitting into. But this will give even more attenuation in the sniffer received signal that may be needed, as the noise source may be quit loud, putting out a lot of RF Noise Energy! But this attenuated ability might just be what the Doctor ordered to allow you isolate the noise souce. And you can always turn up thre RF Gain if need be.
With the sniffer coax, you can test the pick up sensitivity by placing it near the coil, or even engine computer, or even the alternator.
When the souce is found, its power leads can have a .01 or .1 uF Capacitor connected to the power lead and ground. This called bypassing the power lead with a Capacitor. A Snap on Toroid Core can have a few windings of the power wire also helping in reducing the noise be transmitted.
Moleculo has had some pretty good results with the noise cancelling speakers, installed in his Jeep. He showd me how some of the noises where significantly reduced or even taken out. Pretty impressive.
The ARRL has great book on RFI, (Radio Frequency Interference) will worth the price. There are at
www.arrl.org
You might have to type in RFI Book in the search window.
Good luck. Its always neat to have someone come back and tell all the radio enthusiats what was the fix.
Jay in the Mojave
www.a1antennas.com
</p>
