Dear Roy: The use of small and large in this context is not clear. So far,
I have found the sizes of type 31 to be about the right size. On the other
hand, some of the 7X types seem only to be available in sizes that are too
small.

Your point that the type, and its performance, is only part of the issue.
One must also have parts that fit.

Thanks, Mac N8TT

--
J. McLaughlin; Michigan, USA
Home:
"Roy Lewallen" wrote in message
news:JZSdnd4om7o7-5DVnZ2dnUVZ_jCdnZ2d@easystreetonline...
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.

A fairly brief look at the graphs (Figs. 6 - 8) shows that type 31 has
roughly the same or a little higher total complex permeability than 73
over most of the lower HF range and same or higher than 43 on up to 100
MHz. So it should be a good ferrite to use for very wide band
applications. However, Table 1 shows that it's available in large parts
only. Type 43 is very widely available in a wide variety of sizes, so you
might have a lot more luck getting cores of the sizes you need in type 43.

Roy Lewallen, W7EL