In article ,
R.F. Collins wrote:

My favorite source for split cores:

http://www.mouser.com/catalog/623/660.pdf

Make sure you order material 31 whiich is effective at all SW
frequencies. Material 43 is not effective at lower frequencies.

The three point chart indicates that even the 31 material might not be
to good at 1 MHz. A lot of the pulse noise from electrical switching is
usually low frequency (in the KHz range) for the fundamental with
harmonics at higher frequencies. The low frequency pulse noise can
saturate radio front ends causing intermodulation products to show up
throughout the range (1 to 30 MHz) of a radio.

--
Telamon
Ventura, California