Topband: Elimination of Treadmill RFI on 160 meters

[Paul Christensen]

> "Bifilar winding of power leads is a two edged sword. While it reduces 
> core
flux from power line currents, it also reduces differential suppression in a
similar fashion. In a tightly coupled choke, the windings simply behave like
a transmission line.  It takes a stand-alone choke in each conductor to add 
significant
differential mode impedances, or a poorly coupled common core choke. You
will not obtain that with a bifilar or trifilar winding."

For a long time, Corcom has recognized this for use in their power-entry 
EMI/RFI filters.  Their high-performance line filters use a combination of 
common-mode and differential-mode components.  In the link below, note the 
use of additional DM filtering in their FC10 product.  The FC10B model uses 
identical CM filtering but lesser differential mode filtering at a reduced 
price.  These filters will typically cure most any junk that appears on AC 
lines of modern household appliances, including switched variable-speed 
motor drives.

http://www.mouser.com/ds/2/418/NG_CS_1654001_CORCOM_PRODUCT_GUIDE_FC_SERIES_0611-370733.pdf

Paul, W9AC