Interference on AM band - Need an in-line filter?

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On my 2000 Sierra, I have an issue with power lines and using the AM band. As in, if I'm anywhere near power lines... I might as well forget listening to any AM stations (garbage/static).

Is this when one would use an inline filter on the feed coming in from the antenna?

FM reception is perfectly fine, and the garbage/static is not coming from the engine/alternator/plug wires. The cause is power lines.
 
I doubt anything will work. Your antenna is behaving properly and just grabbing what's "out there" which sadly includes interference.
 
This is normal behavior for AM. AM means amplitude modulation. Any electro-magnetic interference, such as that coming trom a power line can add itself on to the AM signal. You hear that interfence in your radio. You don't hear it with FM, because it's frequency modulation. EM interference doesn't change the frequency so it doesn't interfere with FM broadcasts.
 
But this is worse than my 2004 Silverado (which is literally the same vehicle).

Something isn't right in the 2000 Sierra.
 
It also depends on how sensitive the antenna, wiring and radio head unit are to the source of interference. Maybe find a vehicle specific forum and see if others have the same issues?
 
Electromagnetic noise on AM usually rides into the radio on the ground shield of the antenna coax cable. You might try skinning back the insulation on the coax and twist a wire around the outer shield, tape it up securely and ground the other end of the wire to clean bare metal in one of the kickpanels under an existing screw or bolt. The new ground may help with the noise. If not, there are antenna noise filters you can buy that may work better. This is one that you can buy from Amazon:

http://www.amazon.com/Scosche-EF014F-10-...na+noise+filter

The GM antenna has a smaller size jack than the standard Motorola jacks on the inline antenna filter. If you use the filter you will also need this adapter set:

http://www.amazon.com/Scosche-Mda-Kb-Mic...antenna+adapter

When using the filters, sometimes they work, and sometimes they don't work. It is a buy it and try it situation. You may even find it takes an inline filter and a splice to ground on the coax shield together to eliminate the noise. You may also need to connect the coax ground splice to the case of the radio as well to eliminate the noise. You may also need to remove the antenna base from the fender and clean the underside of the fender and the metal mounting base of the antenna with a wire brush. Sometimes corrosion and dirt at those points can cause noise problems. Noise can usually be eliminated but it can often take several different solutions and some trial and error to fix the problem.
 
It could be the antenna, it could be the cable or it could be simply that the tuner is not particularly good in that model. You'd have thought by 2000 they'd have learned to make a good selective tuner, however it might be just a dud design (or unit) that slipped through the net (cost saving on components?).

I've noticed several times over the year significant improvements in radio performance by replacing the head unit with a better model. More sensitive, more selective.

Having said that, if it used to be ok then it's likely to be something else.
 
As mentioned it's either antenna, cable or head unit, no other cause...

Older radios required peaking on AM band via a trimmer, those had a adjustment that was supposed to be set for best reception on a weak station... AFAIK those disappeared in the '80s...

Before FM was common car radios used a extendable antenna of approx 5ft max that was still too short for optimum reception... Once FM became common antennas were fixed at approx 31" as that's it's optimum length...
 
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