AM band filter

Topic: AM band filter (Read 763 times) previous topic - next topic

AM band filter

February 22, 2009, 08:16:06 PM

I am interested to see if anyone has an idea or solution to a better coil / alternator filter so the AM bands do not pass to the speakers.

The wifes 1990 bronco has a filter up on the coil but this is probably only due to it being mounted directly on the engine.

Some of my stations while on, i can actually hear the engine rpm's and shifting noise passing through like a buzzing noise.

what combo of capacitor / resistor or whatever would work to get rid of the noisy reception?

AM band filter

Reply #1 – February 22, 2009, 08:43:06 PM

A radio noise surpressor should cut the alternator/ignition noise coming through your radio, but AM is notorious for picking up any RFI, so it'll be hard to eliminate completely. You can try a shielded power wire but it'd require some custom wiring. We use shielded wire for RADAR plugs in cop cars to eliminate the possibility that RFI will bugger the RADAR readings. This is especially a problem with strobe light equipped cars.

If you ever get the chance, sit in a cop car and tune the radio to a blank AM station. Then turn on the strobe lights. You'll think you're in a Star Wars movie :D

AM band filter

Reply #2 – February 22, 2009, 09:06:38 PM

does this shield process follow suit with most shielded wires where the shield is grounded on on end only? the shield acts as an antenna and puts any AC straight to ground. I have plenty of shielded wire laying around.

Maybe I need to look at the evtm and see if there is a shield called out for on the radio. I might have a problem instead.

This is on my 20th.

AM band filter

Reply #3 – February 22, 2009, 09:10:52 PM

nope,, i dont see a provision for a shield. Ive seen a shield in various wires throughout various pages but not on the radio.

I wonder why the bronco has the filter / condensor and the passanger cars dont. The wifes bronco has no problems with AM bands like the coug and its an aftermarket radio on the bronco as well.

AM band filter

Reply #4 – February 22, 2009, 09:50:54 PM

The aftermaket radio probably has built-in noise surpression that is better than the Ford radio.

Does your Cougar have premium sound? You could be picking up RFI at anywhere between the head unit and trunk mounted amp (though this is unlikely if your problem only happens with AM).

The factory power wires are not shielded. For best results a shielded wire should be grounded at both ends, at least that's the way the RCMP radio workshop insists we do it - might be because strobe wires are high voltage though. You might also make sure the big red ground wire (yes, the factory radio ground wire is red - why, Ford, why???) is making good contact on the stud on the back of your radio.

There is also the chance the radio antenna base is not grounded well...

AM band filter

Reply #5 – February 22, 2009, 10:08:38 PM

When I was doing my CB thing, I had to add a bigger motor to body ground. This took care of alot of it.

AM band filter

Reply #6 – February 23, 2009, 12:02:01 AM

yeah its only on AM ,, I really dont see the point in doing a shield wire from the fuse box to the radio,, it might help but something tells me I have to put more attention at the source. Im not really sure, I suppose I can easily do what you said though and jumper in a shielded power wire.

AM band filter

Reply #7 – February 23, 2009, 12:51:56 AM

The last time I had this problem, the antenna cable shield was not grounded at the fender end.

AM band filter

Reply #8 – February 23, 2009, 10:13:01 PM

This shouldnt be that hard to check first, although it is power antenna , i may be fooled.

I have a healthy list of things to look into which will take up a day in the garage on a cold day. should be fun.