Well, I don't think there is a "one-size" or "one--mix" "fits all" preferred solution. I've wanted to try some 31 mix cores for common-mode isolation at 80 and 160. On the other hand, some of the Fair-Rite 71 (73?) material toroids and binocular cores provide really good performance, even at lower frequencies, because of the lower losses and better frequency response.
I also suspect that for power handling applications ( including common-mode suppression), the 31 mix might have some heating issues, because of the higher losses. BTW, I do know from experience that the Fair-Rite 71/73 etc. mix higher frequency cores seem to be impervious to weather! I have used the tubular cores and large binocular cores out of doors for years as common mode chokes on RG-213 for my 5-band quad feed-line and to make quick home-brew W2DU 1:1 current baluns for vertical dipoles for. 30 and 40 meters. I've never seen any evidence of corrosion nor have I noted any performance degradation. I've used the binocular transformer cores to construct matching transformers for "KAZ" terminated receiving loops for 160.80.40 and 30 m and use a larger binocular core to match 50 ohms up to the cathode impedance of my home-brew 3-500ZG amp, to avoid having to install a much more complex band-switch. Works quite well 160-10m and comfortably handles everything that my FT-1000MP delivers. Fortunately I had a good selection of cores in my Fair-Rite developer kits from my engineering days! 73, Charlie, K4OTV -----Original Message----- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI Sent: Wednesday, August 06, 2014 3:09 PM To: Ron Stordahl, AE5E; topband@contesting.com Subject: Re: Topband: Ferrite Cores In this discussion two different ferrite mixes are mentioned: #31 and #61. >From the descriptions of these on the Fair-Rite web page, it appears that 31 would be more suitable for lower frequency applications. >>>> Core selection can be fairly complex in transmitting systems. I've yet to see a case where one core mix is the be all end all for the range of things you run into in the field. Especially at high common mode impedances. Receiving is a completely different story, because core stresses are always low. 73 Tom _________________ Topband Reflector Archives - http://www.contesting.com/_topband --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com _________________ Topband Reflector Archives - http://www.contesting.com/_topband