[Elecraft] Elecraft Digest, Vol 79, Issue 18

[George Dubovsky]

DC for variable-speed has been largely supplanted by ac, multiphase motors
over the last 20 years. There is ac-dc conversion in the front end of the
controllers, but it is then followed by dc-ac single or, more commonly,
three-phase, variable frequency generation. That's usually the source of the
noise. The quietest (EMI) variable-speed drives are the ones that most
closely generate a sinusoidal waveform. Since that costs money, most are
kinda noisy. There are input and output line filters sold for variable-speed
drives, and sometimes they are available on epay. Hitachi is one of the big
manufacturers of VSDs  that comes to mind.

73,

geo - n4ua

On Wed, Nov 10, 2010 at 3:40 PM, BOB PHILBROOK <k9pag at msn.com> wrote:

> DC motors?  BEt so if they are variable speed.
>
>  If so, AC to DC conversion might be part of your source of RFI.
>
> Bob, K9PAG
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