Topband: Elimination of Treadmill RFI on 160 meters

[Jim Brown]

On Wed,1/28/2015 8:34 AM, Brad Rehm wrote:
> I've never looked closely at the problem, but I wonder how the 31-mix cores
> behave in the presence of high-current, 20 kHz fundamental frequency pulses
> that drive the PWM motor in our treadmill.  That mix would suppress the
> higher-frequency harmonics, but would the core eventually change its
> properties because of the transients it has to live with.  (The load
> current rating of our treadmill was 15 Amps.)  Is it possible the core
> could begin to generate more noise at Topband frequencies if it became
> easier to saturate?

Several points. First, RF current on the green wire will couple to the 
other conductors, so ALL conductors should be run through the common 
mode choke. Second, since all conductors are going through the choke, 
the baseband magnetic field (that is, 60 Hz and harmonics of 60 Hz) is 
zero unless the load device is miswired with neutral connected to the 
green wire and the load device is grounded.

Except for lightning, your concerns with transients changing the core is 
not at all warranted.

Based on my experience with noisy stuff, I always apply the common mode 
choke as close as practical to the noise source, and nearly all of my 
various electronic loads are plugged into multi-boxes into which I have 
installed a line filter.

We're lucky out here around Silicon Valley in that we still have a big 
electronics surplus warehouse. One thing they had a lot of several years 
ago was a selection of AC line filters from Delta, Corcom, and a few 
smaller vendors. I bought a bunch for a buck or two apiece. 
http://www.halted.com/

73, Jim K9YC