I have an Alpine AM/FM/CD unit in my truck. On the AM, and ONLY on the AM, I get static. Now, I am old enough to remember when a small capacitor on the generator (they used to be called generators) caused this problem. It is not as loud as the old type hum, but goes up and down with RPM. It is also worse when I have my truck rack on the truck. At low RPM, I can hear the radio, but at high RPM, I just get static. FM works with NO static at any time. Anyone here had the same problem? Any quick fixes or magic bullets?
An alternator will cause a continuous whine to be heard through the speakers, varying with RPM. A capacitor across the +ve output terminal and ground can sometimes cure this. The greatest cause of interference on AM bands in my experience is poor grounding of the aerial to the vehicle body, a non-continuous aerial co-ax cable, or a problem with the radio itself. The static type interference is usually from the ignition system or other motor that runs continuously, such as a fuel pump.
Is the tip of your antenna intact? If you have a sharp end, you can get noise. The solution I've heard is to put a tennis ball on the end (or something similar). I haven't tried this...
If it were coming in the DC lines, it would be there in the FM also. FM being noise limiting by virtue if the modulation system itself, (Noise pulses clipped and eliminated, only frequency variations causing an output) static is clipped and eliminated before the audio stages. If it were coming in the DC, you'd hear it on FM also. This leaves the antenna, and the problem of deciding where it's being generated. Antenna cable, as has been mentioned, is a place to start, But where it's being generated and how to eliminate it can be frustrating. Putting the rack on may be causing some blanking of the antenna, cutting the signal input, and making the static seem worse. Any ground cables that are loose or corroded can cause it, they're not the cause, but don't eliminate the static as they should. A bad ground shield on the antenna plug can be another, anything that goes to ground can allow the static to be radiated rather than grounded if the connection is not good, and at low voltages, the degree of which it has to be bad can be very small. Check anything that's supposed to be grounded, but no guarantees there either. Chasing static is pretty much of a crap shoot.
If the sound is more a tick tick sound rather than a humming type static, the problem is the ign. system. Fresh wires and plugs may fix or relieve the problem a bit but it will probably still be there. If the sound is a humming type then the alternator is probably at fault and attaching a condensor to the output of the alternator at the alternator should decrease that a lot. AM radio is a lot more suceptible to noise as it is an amplitude modulated system and thus any noise tends to sound like the signal.
-- Bob May Losing weight is easy! If you ever want to lose weight, eat and drink less. Works every time it is tried!
As already mentioned - there should be a capacitor (from the factory) somewhere around the distributor (don't know what kind of vehicle you have) or the ignition block feeding the spark plug wires. The cap may have bad connections itself, or simply need replaced. It won't hurt to add a few caps here and there (like on the heater fan motor, etc), but also look for a little scraper type deal from the inner fender or the firewall which is supposed to "scratch" the underside of the hood everytime it's closed - makes the hood part of the rest of the body metal. It may be a flexible copper wire braid strap bolted to both, but look for it, clean it up and make sure it's tight. HTH Ken.
Yup. Definitely a tick tick rather than a melodious hum. Will look at the wires at night. Been a good while since a tune up, too. Since it could use a tune up, am going go have that done, and then see if it persists. I take the rack on and off, but would like to have it work at all times.
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