On 6 Oct 2003 07:24:22 -0700, (Lydokane) wrote:

This is a repost of a message that I posted through google... almost
two weeks ago. It finally got posted yesterday.

I have a hard drive based MP3 player. It is designed for automobiles
but with a transformer I can use it in the house or at work. The
problem is it puts out a large amount of RF interference. When I am
at home it isn't a big deal. When I am in the car or at work it
becomes a problem. The player literally wipes out the entire FM band.
Every station turns to static (actually you hear the wirring noise of
the hard drive). I am sure it is ‘airborne' interference. If I am in
the car and I pull up next to somebody, and their radio is loud
enough, I can hear my interference from their radio. Naturally, it
also affects my radio. At work it is even worse. I work in a
factory, which is mainly a steel, and cinder block building. With the
push of a button I can render every radio in the shop useless. I have
been told not to bring it back, unless I want to be flogged, tarred
and feathered.

What could be causing the interference? I know the unit has a regular
3.5" hard drive. I don't believe this could be the problem because we
have several (about 12 or 15) computers on the shop floor that all use
a 3.5" HDD. I know the unit has a eprom that is programmed to decode
the MP3 files and I think it has a small processor. It doesn't run
any kind of internal amp. Since it is designed for use in an
automobile it is drawing 13-14 V and 3amps.

What could I do to reduce/eliminate the interference?

Thanks,

I'm assuming this thing doesn't have a transmitter inside it? You
don't play it through your FM radio by tuning to a specific frequency?
Do you plug something into the tape to get the music from the player
to the audio system in the car? How does the music get from the
portable drive to the speakers? or are you using head phones?

Does it get power from the cigarette lighter socket? Does the power go
into the drive at the same connector at the factory and in the car?

Does the interference vary in frequency with the speed of the engine?
You say it isn't a problem at home but only in the car/factory - is
that because it is less noticeable or less objectionable (but still
there) or gone entirely? That would be a clue.

Changing the position of the player matter?

Try one of the inexpensive clamp on (clamp around ferrite core) line
filters from Radio Shack on the power to the HDD on the 12V to it.
(close to the drive- not the power source) You may have an internal
DC/DC convertor broadcasting RFI.

If the case is metal try grounding it, to the body of the car.

If the RFI seems dependant on the speed of the drive it is the drive
motor circuit doing it (you may hear that as it spins up to speed as
an increase in frequency) The broadcast path can still be the power
leads so the clamp may work.

If the clamp on ferrite filter just attenuates the noise, don't
despair, rejoice - you're on the right track and that's a good start.
The next thing to try are two chokes and/or sheilded power wires and a
ground.

Shields on wires should be grounded at one place (END) only.

If it depends on the speed of the car's motor, that's a different
game, you may need one of the inductor/capacitor filters on the + lead
of the power to the unit. If that's the case - it works better if the
frame (metal mounting - not the power lead!) of the inductor is
grounded to the car body. That, of course, probably won't fix the
factory problem.

If it is transmitting through the FM radio, as a way to get from the
mp3 player to the car's speakers, that opens a whole additional
trouble shooting tree.



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