Problem with audio whine (sounds like alternator) through earphones.
Device is GPS unit w/ 4 wires: Standard positive (12 volt) and negative
leads, plus two to headphones.

When installed on vehicle, alternator whine is present and loud in
headphones.

Removing the fuse (in positive lead) and running the GPS on its own internal
battery it still produces whine. Note negative lead is still to chassis
ground strap so it may be coming in on that?? (or maybe RF noise?).

Is it possible to get alternator whine through the ground strap alone?

I took a Fluke ohmmeter and measured between the battery's negative post to
the bolt where the ground strap is. Maybe 0.2 ohms. If the key is turned
on, the resistance goes up to around 8 ohms (?, between ground strap and
battery negative still). Switching the Fluke to millivolt scale it shows
maybe 2.5 millivolts on the DC scale.

Prior, I've tried a power supply noise suppressor on the positive lead to no
avail. Still whines.

Can whine come through an amp on the negative lead alone, even if the unit
has it's own internal battery as this GPS does? I cannot believe it could
be RF noise the unit is picking up (not any room to move the device to try
that).

I have access to an oscilloscope. Don't know if I'd see anything on either
the ground or positive leads though since the noise still comes in without
the positive lead attached (fuse out).

Ideas anyone to eliminate this alternator-like whine (goes up and down with
engine speed)? It's driving me nuts!

Tia.

B~

On Sun, 22 May 2005 02:37:51 GMT, "B. Peg"
wrote:

Problem with audio whine (sounds like alternator) through earphones.
Device is GPS unit w/ 4 wires: Standard positive (12 volt) and negative
leads, plus two to headphones.

When installed on vehicle, alternator whine is present and loud in
headphones.

Removing the fuse (in positive lead) and running the GPS on its own internal
battery it still produces whine. Note negative lead is still to chassis
ground strap so it may be coming in on that?? (or maybe RF noise?).

Is it possible to get alternator whine through the ground strap alone?

I took a Fluke ohmmeter and measured between the battery's negative post to
the bolt where the ground strap is. Maybe 0.2 ohms. If the key is turned
on, the resistance goes up to around 8 ohms (?, between ground strap and
battery negative still). Switching the Fluke to millivolt scale it shows
maybe 2.5 millivolts on the DC scale.

Prior, I've tried a power supply noise suppressor on the positive lead to no
avail. Still whines.

Can whine come through an amp on the negative lead alone, even if the unit
has it's own internal battery as this GPS does? I cannot believe it could
be RF noise the unit is picking up (not any room to move the device to try
that).

I have access to an oscilloscope. Don't know if I'd see anything on either
the ground or positive leads though since the noise still comes in without
the positive lead attached (fuse out).

Ideas anyone to eliminate this alternator-like whine (goes up and down with
engine speed)? It's driving me nuts!

Tia.

B~

Go to Rat Shack and pick up an RF choke coil. Get the biggest they
have.

B. Peg wrote:

Problem with audio whine (sounds like alternator) through earphones.
Device is GPS unit w/ 4 wires: Standard positive (12 volt) and negative
leads, plus two to headphones.

When installed on vehicle, alternator whine is present and loud in
headphones.

Removing the fuse (in positive lead) and running the GPS on its own internal
battery it still produces whine. Note negative lead is still to chassis
ground strap so it may be coming in on that?? (or maybe RF noise?).

Is it possible to get alternator whine through the ground strap alone?

I took a Fluke ohmmeter and measured between the battery's negative post to
the bolt where the ground strap is. Maybe 0.2 ohms. If the key is turned
on, the resistance goes up to around 8 ohms (?, between ground strap and
battery negative still). Switching the Fluke to millivolt scale it shows
maybe 2.5 millivolts on the DC scale.

Prior, I've tried a power supply noise suppressor on the positive lead to no
avail. Still whines.

Can whine come through an amp on the negative lead alone, even if the unit
has it's own internal battery as this GPS does? I cannot believe it could
be RF noise the unit is picking up (not any room to move the device to try
that).

I have access to an oscilloscope. Don't know if I'd see anything on either
the ground or positive leads though since the noise still comes in without
the positive lead attached (fuse out).

Ideas anyone to eliminate this alternator-like whine (goes up and down with
engine speed)? It's driving me nuts!

Tia.

B~


Alternator whine can travel electromagnetically, jumping across wires.
That's why good audio installers make it a practise to run the power
wires far away from the wires carrying the audio signal. Far in this
sense is about 1 foot or more.

CD