JIMMIE wrote:
On Apr 21, 10:21 am, "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.

--
J. McLaughlin; Michigan, USA
Home:


I think the type 31 is entended for use on things like power cords and
computer cables to prevent unwanted radiation/pickup of RF. Im not
sure how well it would meet your requirements but I suspect it may be
OK in a receive only situation. I have tried using some unknown types
of cores removed from various computer cables for a balun and the
vinyl tape holding them to the coax got very soft when they heated up.
Perhaps some experimentation using these cores is in order.

Jimmie

#31 is specifically made for our kind of application (transmitting).. it
has a higher temperature rating than the other popular materials. The
key on managing dissipation is making sure you have enough impedance so
that the current is small.

It's a long way from the miscellaneous stuff used for RFI on power cords
and keyboards..