Common-Mode Chokes1
by
Chuck Counselman, W1HIS
Excerpts:
This article tells what common-mode chokes are, why and where to use them, and how
to make ones that work well, at minimal cost both in time and in dollars.
In the HF hamshacks that I’ve visited, the background noise level heard on most HF bands (especially the low bands) could be reduced by more than an S-unit by means of common-mode choking. In some cases (which I could name but won’t, to avoid embarrassing my friends) I was able to reduce the received noise level by four or five S-units. I reduced my own received noise level on the low bands by even more.
http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf