J. Mc Laughlin wrote:
I looked through saved messages and the only reference to type 31 ferrite
(Fair-Rite) was in March of 2005. That reference had to do with ignition
wires.

Recommendations for HF choking ferrites have centered on the 70 series with
type 43 being favorably recommended for the upper portion of HF and VHF.
However, Fair-Rite seems to be recommending type 31 for HF. See Figure 26
in:
http://www.fair-rite.com/newfair/pdf/CUP%20Paper.pdf

Am I missing something? It seems to me that for the purpose of choking
common mode current (on the outside of the outer conductor of coax) from 3
to 25 MHz one should prefer the use of type 31. This is a receiving
application with a long run of coax.

73, Mac N8TT

P.S. I will also appreciate ideas about places to purchase ferrite in
addition to Mouser.


Fair-rite 31 mix is a new one specifically developed for RF choking
applications. As you mention, it has a huge range of frequencies for
which it's useful. The recommendations one sees in older literature for
73, 43, etc, were formulated back before the new mix was available. Of
course, once something is written, it gets copied over and over without
a lot of thought being put into whether the underlying assumptions are
still met: in this case, what mixes are available.


Page 888 in the Mouser catalog shows some 31 mix parts..
http://www.mouser.com/catalog/633/888.pdf

You can also go to Fair-rite's website and find a list of their local
distributors (Lodestone Pacific, for instance).

The 3&4 digits of the part number are the mix:

xx31yyyyyyy is a 31 mix part.