[RFI] Common Mode Choke Materials

[Tony]

All:

Thanks for the info on LF/MF common mode chokes. Jim's (K9YC) cookbook 
is very informative. I did some preliminary testing on 160 and 80 meters 
with a couple of 2.4 inch mix31 cores I had on hand using 16 turns of 
RG-178.

I was surprised to see that the choke was much more effective when 
placed at the SDR Play receiver than it was at the antenna (active 
loop). The noise floor dropped 15db with this configuration and only a 
few db with the choke placed at the antenna.

My guess is that the bulk of the noise is coming from the PC connected 
to the SDR since the only things on in the shack were the PC and 
monitor. I placed another choke on the USB cable that connects the two 
devices, but that had a minimal effect.

I'm seeing -120 dbm noise floor on 160 and -130 dbm on 80 with the 
simple mix31 choke and the active loop so I'm happy about that. It 
doesn't do much for bands below 160, but I guess that's to be expected.

Tony -K2MO