On Apr 29, 3:27*pm, "Charles" wrote:
"amdx" wrote in message

...





I have an undercounter AM, FM radio. When I plug the power supply to my
laptop
into an outlet in the same room, the FM signal gets very noisy. Upon
further investigation, I found that just plugging the ac cord into an
outlet and holding it near the laptop causes the noise. Also holding the
laptop near the power cord of the radio causes the noise. Holding the
laptop near the radio doesn't cause the noise.
So I think the laptop is generating noise that gets induced into the ac
line.
I tried wrapping the radio cord about (ten turns) through a (junkbox)
toroid without any help to the problem. The toroid is 3" in dia. It's
probably an iron laminate core
(low frequency) so may not be right for filtering the ac line.
*My next step is to go to Radio Shack and try to purchase some clamshell
type
line filters.
* Any ideas to eliminate this noise from the ac line?
* * * * * * * * * * * * * * * * * * * * * * * * * * * Mike

Switch-mode power supplies are dirty ... lots of harmonic energy. *The
interference is both radiated and sent back into the ac mains. *A line
filter plus physical separation are the things to try.

Some clocks for digital devices are intentionally "spread spectrum"
since the digital stuff doesn't care. This helps pass FCC type
acceptance. Spread spectrum is FM noise.

I remember that IC company IMI used to make SS clocks for digital
stuff. I wonder what ever happened to them.


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