[M OSFET]

Well, OK, it deinately sounds like you have studied the problem and I
suppose against all better judegment I am forced to agree with you that the
interference is coming from power lines.

Sooooooo......

The first thing we need to determine is whether the interference is
effecting the radio directly. What I mean by this is if you were to
disconnect the anntenna, would the problem still exist? If the answer is
yes, you may just plain have a faulty HU.

If the answer is no, then as Greg pointed out, you need to devise an anntena
that, as best as possible, pulls in AM stations and rejects EMI.

Honestly, I keep trying to think "out of the box" on this one as I have
NEVER heard of such a problem occuring with your basic suburban
side-of-the-road power cable.

I keep trying to figure out if it is something else that is causing the
interference when near a power wire. Greg is certainly on the right track
in sugesting you try a small portable AM radio in your car and see if
anything strange occurs.

This is a shot in the dark, but perhaps you have yet another EMI source,
perhaps originating in the electrical system of your car, and the presense
of the small amout of EMI from power cables somehow pushes this interference
"over the edge" and becomes audible. Again, just a guess.

I know this sounds like a lot of work, but I might sugest just plain
completely re-installing your HU. THere are a thousand things that may have
gone wrong with the initial install causing the problem.

I mean, a good quality aftermarket tuner, like the one you have, SHOULD NOT
do this. I wish I had the answer and could tell you to change this to this,
but again, this is a new problem for me. When I have had problems I
couldn't erradicate, it's surprising how just re-installing the entire thing
will often fix it.

Other than that, I don't have any other advice other than possibly returning
the HU as it sounds like it may be defective.

Good luck,
MOSFET

"Bob F" wrote in message
...
The noise only occurs when I am driving near power lines. It varies as the
lines nearby change. When there is no powerline close to the road, there
is no problem. The distortion/modulation is bad enough at its worst to
make to understanding the spoken word difficult. The problem depends
entirely upon my location. Each time I drive by the same bad spot, the
problem recurs.

MOSFET wrote:
First off, Greg knows much more about EE matters than I so I defer
any and all questions of a technical nature to him.

HOWEVER, that being said, I DO know that your car's engine
(alternator, sparg plugs, ect.and other accesories in your car) emit
more EMI (electromagnetic interference) inside your car than your
typical suburban power lines along side every residential rode. In
my 25 years involved in car audio, I have NEVER heard of problems
caused by your ordinary power cable.

True, when I have gone near LARGE CURRENT bearing cable like from a
damm or reactor to a substation I do encounter noise over my AM band.
I really don't think there is anything you can do about that as the
EMI just plain over-powers and distorts all AM signals. There's no
way for your radio to discern what's an AM signal and what's EMI on
the AM band, a little like going through an "EMI" tunnel. But those
type of massive lines tend to be few and far between

But again, I have NEVER heard of plain old suburban power cable
causing EMI. There just isn't enough juice going through those wires
to create the kind of interference your describing, unless, again,
you live near VERY large current bearing cable.

I'm curious, how did you deduce it was the power cable causing the
interference? Are you sure that's the source?

MOSFET


"GregS" wrote in message
...
In article , "Bob F"
wrote:
I recently acquired a 1994 Dodge Caravan with a pioneer supertuner
AM/FM radio.

It has bad problems on an AM staion I listen to whenever I am near
powerlines. There is a 60 Hz hum that modulates the audio causing
bad distortion. I thought

this would be a grounding problem, and have tried adding an
additional temporary
ground at either end of the antenna cable, with no effect. Can
anyone offer any

help in solving this?



Is it hum or buzz. I'm thinking buzz.
I don't think i ever encountered this, but power lines will emit
noise. Is the noise all across the band ?
A different type of antenna may help. I'm thinking a big loop on top
of the roof.

greg