On Fri, 01 May 2009 20:49:11 -0600
Art <k6xt@arrl.net> wrote:
> ...noisy pumps and their
> cures. Last winter the gas wells on my place were
> converted to electric motors.
Art,
From your description of the noise it is hard to say what
generates it, but I got a feeling that it may come from a
Variable Frequency Drive. These are essentially solid
state AC power supplies that use a single phase 230 V AC
input to generate a three phase 10 to 60 Hz variable
frequency simulated AC output that is formed by a series
of modulated 2 to 10 kHZ pulses. From the point of view of
driving motors, they are fantastic: efficient, easy speed
control, all kinds of programming features, etc. From an
RFI point of view they are weapons of mass destruction!
The inputs are easy to filter, just a regular RFI filter
(Corcom, whatever), but the outputs require very special
(and expensive) filtering and shielding. Once you have
determined that it is a VFD that generates the noise, and
you can get access to it, I will be happy to provide you
details on the filtering of the outputs.
Unfortunately, we will be seeing these more and more
often, not only in industrial applications but even in
home appliances.
GL,
George
AA7JV
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