On Sat, 25 Apr 2009 23:07:49 -0700, Vic K2VCO wrote:
>and I disagreed, because the number of cores is irrelevant -- it's the total
>length of the
>cores that counts, not the number. If the usual cores are 3/8" long, these are
>each worth
>three of them, so five of these cores are the same as 15 of the usual size.
>15 cores of #31 material make a pretty decent choke, at least above 3.5 MHz.
It depends entirely on your definition of "a pretty decent choke." My MINIMUM
definition of
an ACCEPTABLE choke are the original W2DU chokes, as published on his website.
Google to
find it. The version of his chokes that The Wireman sells uses 50 beads. One of
Walt's
designs used 200 beads. THAT is a pretty decent choke. Five 1-1/8 inch cores of
#31 is
pretty poor choke in the HF spectrum.
I've addressed all of this in great detail in my tutorial, including plots of
the impedance
of strings of 1-1/8 inch #31 cores. I'm not going to repeat it in an email
discussion. The
multi-turn chokes I've designed using #31 toroids are significantly better than
Walt's 200-
bead chokes (which have 4X the choking impedance of 50-bead chokes).
BTW -- when I first published my work on coaxial chokes several years ago, Walt
sent me a
nice email saying he liked my work and the way I discussed it as building on
his. Note that
Walt published nearly 30 years ago, when #31 did not exist, when #73 was the
only suitable
material, and when it was only available in the small beads that only fit small
coax. I
think his engineering was first class.
73,
Jim Brown K9YC
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