Yes, this is related to the noise cancelling device described at
http://www.geocities.com/g4lna/noisdes.html

I'm trying to figure out if I can substitute type 61 or type 43
ferrites for the transformers, because I have these ferrite ring cores
but I do not have the iron powder toroids. Also, using type 43
ferrites would allow me to use fewer turns. (That 160m/180m
transformer requires about 50 turns!) From my experience with
high-power RF transformers, I know that iron powder toroids are less
vulnerable to core saturation and excess heating.

The phase shifter and the amplifier in the noise cancelling device do
NOT work with high power levels like a transmitter, tuner, or
SWR/wattmeter would. So if core saturation and excess heating are not
an issue, is there any particular reason I MUST use iron powder
instead of ferrites?

Jason Hsu, AG4DG