On 6/16/2021 8:33 AM, jim.thom jim.thom@telus.net wrote:
It will only handle a maximum of a 2.4 inch OD type 31 core. K9YCs
latest designs all use the much larger, I think, 4 inch OD cores.
No, I studied both the larger cores and the more commonly used 2.4-in
o.d. cores, and MOST of my designs are for the 2.4-in cores.
As per number of turns, is this for wire, or coax, or can be used for
either ? If coax used, what type of coax ? I used RG-303 and RG-400
on the smaller CM chokes....and RG-393 on the bigger CM chokes.
My designs are for RG400, #12 PTFL pairs, and #12 pairs from Romex.
Looking at the various attributes of a type 31 2.4 inch OD toroid, by
both fair rite..and also amidon, I am not seeing any difference in
properties between the 2 x manufacturers.
Amidon is NOT a mfr. They are a reseller of Fair-Rite, the inventor and
ONLY mfr of #31 material, and they started making 2.4-in toroids with
that material because I ASKED them for it in 2004 when I was beginning
research on RFI to pro audio systems.
On a side note, N3RR, Bill Hider, a few yrs ago, bought 700 (seven
hundred) of the type 31, 2.4 inch OD cores...from I think, Fair
rite..... and the tolerance between all of em was strewn all over the
map, like + or - 20+ %. Bill came up with a simple 1 turn test to
evaluate,and then grade them into various groups. Some time in the past,
apparently Fair rite moved their production facilities to CHINA, and
after that, the ± tolerances went all to hell.
There is no evidence that their production deteriorated when they
established their facility in China. As part of my work to develop my
Choke Cookbook, I measured 10-turn chokes wound with a single piece of
RG58 on more than 200 cores; roughly half were 2.4-in o.d. cores,
purchased over nearly 15 years from Fair-Rite directly and from 3-4
industrial vendors, including the first five pre-production engineering
samples that Fair-Rite sent me in 2004. The 4-in o.d. cores were a
single group purchase for members of our contest club from a single
vendor about five years ago.
My measurements of those 200 or so cores was intended specifically to
address manufacturing tolerances, which have a profound effect on HF
chokes wound on these cores. ANY competent engineer designing something
for production must take these tolerances into account. To produce my
cookbook, I put measurements of my reference winding on all of those
200+ cores into spreadsheets, one for each cores size, and selected
cores at the limits (i.e. worst case) on which to wind chokes to produce
my designs. I then wound chokes on those "limits" cores with all of the
winding materials (RG400, #12 PTFM and #12 NM), measured them starting
with 18 turns (for the 2.4-in o.d. cores), snipping a turn, down to
where their resonance was higher than 30 MHz, and remeasuring. For each
measurement, leads had to be snipped to "zero length" so that lead
inductance did not add measurement error (I was measuring a parallel
resonant circuit).
All that data went into a spreadsheet, with data points at limits of
160, 80, and 40M bands, centered in 20 and 15, and at around 28.5 MHz,
and for each winding (turns, winding material), worst case of Rs (lowest
value) was used to develop the Cookbook. The result is that a ham using
the Cookbook will have a choke that is equal to or BETTER than those
minimum values.
Before he died several years ago, G3TXQ published recommendations for
chokes, some of them using #31 material, others using #43 and #52. After
finishing my Cookbook, I bought 40 #52 cores from four US industrial
vendors, 10 pieces from each, over a period of about two months,
repeated my process of measuring my "reference" winding on each, and
selecting limits cores. I then wound chokes following his
recommendations on "limits" cores and measured them. I was unable to
duplicate his results on any of those "limits" cores.
Steve was clearly a great scientist, and clearly knew how to measure
correctly. What he apparently failed to understand was manufacturing
tolerances -- I suspect that he measured no more than a few cores of
each material. The shortcoming of NiZn materials like #43 and #52 for
use on HF is that they are much higher Q, so manufacturing tolerances
have far greater effect on the resonance of multi-turn chokes than #31,
which is a VERY SPECIAL MnZn material, which has a dimensional resonance
within the HF spectrum and lower Q winding resonance that makes it's
impedance curve much broader.
To understand these concepts, I recommend a study first of
k9yc.com/RFI-Ham.pdf and then the Choke Cookbook. Note that I said STUDY
-- I'm an EE, and it took me a decade of serious study to understand
this stuff!
73, Jim K9YC
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