Motors with brushes are "incidental radiators" according to the FCC. I
believe PWM or variable frequency drive motors would be considered
"unintentional radiators" in that they intentionally generate a radio
frequency (9 kHz to 3,000,000MHz) but do not intend to radiate it. (see
definitions at http://www.hallikainen.com/FccRules/2007/15/3/).

Incidental radiators must use good engineering practice to minimize
interference (see http://www.hallikainen.com/FccRules/2007/15/13/).

Digital devices (I think motor control systems qualify as digital
devices) in appliances are exempt from the emission limits for
unintentional radiators (see
http://www.hallikainen.com/FccRules/2007/15/103/), though the user must
cease operation if the FCC finds it is causing interference.

On 12 Nov 2006 20:38:46 -0800, wrote:

Motors with brushes are "incidental radiators" according to the FCC. I
believe PWM or variable frequency drive motors would be considered
"unintentional radiators" in that they intentionally generate a radio
frequency (9 kHz to 3,000,000MHz) but do not intend to radiate it. (see
definitions at http://www.hallikainen.com/FccRules/2007/15/3/).

And Part 15 limits the emissions from Unintentional Radiators, but the
limits are so high as to be of almost no protection to
radiocommunications within a hundred of metres or more of the emission
source.

Owen
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