Attention: TDR Forum Junkies 
This is for information.
95 4whl drive, standard radio/tape deck.
We travel remote areas, Canade, Alaska etc. Much of the time we can only pick up AM radio stations. I have always been bothered by a slight whine in the background of very weak AM radio stations. I finally decided to trace down the noise. It comes from noise on the DC feed to the radio. The noise, in my case comes from the insturment panel (removing the fuse to the air bag/insturment panel kills the noise.
Looking at the DC feed (with an oscilloscope) shows a 20mv niose spike at about 20Khz which interacts with the phase locked loop in the radio local oscillatior.
I was able to kill the noise by installing a choke (30 turns of #22 wire around an old portable radio ferrite core).
An alternative solution would be to run a seperate wire back to the battery. Thae noise was on the supply line, not the ground.
Rog
95 4whl drive, standard radio/tape deck.
We travel remote areas, Canade, Alaska etc. Much of the time we can only pick up AM radio stations. I have always been bothered by a slight whine in the background of very weak AM radio stations. I finally decided to trace down the noise. It comes from noise on the DC feed to the radio. The noise, in my case comes from the insturment panel (removing the fuse to the air bag/insturment panel kills the noise.
Looking at the DC feed (with an oscilloscope) shows a 20mv niose spike at about 20Khz which interacts with the phase locked loop in the radio local oscillatior.
I was able to kill the noise by installing a choke (30 turns of #22 wire around an old portable radio ferrite core).
An alternative solution would be to run a seperate wire back to the battery. Thae noise was on the supply line, not the ground.
Rog
