Generally, Mix 43 and Mix 77 are the best for attenuation in the HF and low
VHF frequencies. For more information, check the Amidon site at:
http://www.amidoncorp.com/aai_ferritecores.htm
Although they are not cheap, I have had excellent results with the FT-240-43
cores, and I would expect that the FT-240-77 cores would work very well at
HF also, especially the lower HF bands.
Ron N6IE
www.N6IE.com
For RF filtering, ferrite with a much higher permeability (and loss at
HF) is preferred to what one would use for a transformer core at the
same frequency. Essentially the higher the permeability the better so
long as the DC or LF current in the wire doesn't saturate the core and
kill off that HF loss.
--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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