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Old April 22nd 08, 03:59 AM posted to rec.radio.amateur.antenna
J. Mc Laughlin J. Mc Laughlin is offline
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First recorded activity by RadioBanter: Jul 2006
Posts: 172
Default Use of type 31 ferrite as coax common mode choke

Dear Jim: Thank you.

I had read an early version of K9YC's work. It was informative to read the
latest version. He does a good job.

It appears that my question may have had a positive effect and
radio-amateurs will consider type 31 for HF.

73, Mac N8TT

--
J. McLaughlin; Michigan, USA
Home:
"Jim Lux" wrote in message
...
J. Mc Laughlin wrote:
Dear Jim:

Now I begin to see light. While type 31 must be at least three years
old, the world has not yet caught up to its existence.


the *amateur* world hasn't caught up.. I haven't looked, but I'd venture
that the ARRL handbook still doesn't mention it (if only because it would
be a expensive and herculean task to revise the entire handbook every
year). And, folks writing in QST tend not to be in the business, so
they're using what they learned in the handbook.

For instance, the RFI/EMC page on the arrl web site says:
"Original text reprinted from February and March 1992 QST "Lab Notes"
columns Copyright © 1992 by the American Radio Relay League, Inc. All
rights reserved."

"Or, you can make a common-mode choke by wrapping 10 to 20 turns of the
antenna feed line or CATV cable through a ferrite toroid. Follow the same
procedure with the ac line. Use #75 (also known as "J"), #73 or #77
material if the interference is mainly from signals below 10 MHz. Use #43
ferrite material for the higher bands or low VHF."

"To make a ferrite common-mode choke, wrap 5-10 turns of a conductor onto
an FT-240-43 ferrite core. (The "240" indicates that the outer diameter of
the core is 2.4"; the "43" designates the material. Other materials may be
useful, but 43 is a good all-around material.)"





(to be fair, they do link to K9YC's writeup)