On 12/19/2025 8:38 AM, Dave Cuthbert wrote:
I use your data and the G3TXQ data for choke design.
I do NOT recommend G3TXQ's data, because it fails to take manufacturing
tolerances into account. Steve was an excellent technician, and I trust
his measurements of the few cores he measured. Before building chokes of
the chosen designs (cable types), I measured more than 100 #31 cores and
selected four at the limits of key parameters, then wound and measured
those design types and tabulated results, by band, in a spreadsheet.
The resulting design recommendations work for cores at the limits of the
cores in my stash.
Fair-Rite makes cores from about 20 different chemical mixes of NiZn or
MnZn. MnZn cores are relatively low Q and exhibit dimensional resonance,
NiZn cores are higher Q and do not exhibit dimensional resonance.
Fair-Rite #31 is VERY special, in that when multiple turns are wound on
it to more its circuit resonance down from VHF to HF, the dimensional
resonance combines with the circuit resonance to have a broadbanding
effect, like what we did when we stagger-tuned the transformers in FM IF
strips. It is that broadbanding that allowed me to publish repeatable
designs for parts that have such wide production tolerances.
To verify my questions about Steve's work, I bought 40 #52 cores, buying
ten cores from four different franchised industrial vendors over a
period of about a month, measured and selected limits cores, and used
them for his designs. I could not replicate any of those designs, using
a test fixture that was nearly identical to his excellent design.
73, Jim K9YC
_________________
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
|