----- Original Message -----
From: "Joe Wilkowski" <k8fc@arrl.net>
>
> Flags and Pennants on the other hand require a larger impedance
> transformation 75:~1000 ohms. Still using a single core 73 mix binocular
> requires a 2 turn primary and a 9 turn secondary. I don't have the
> equipment to measure the interwire capacitance but it is significant as it
> relates to common mode noise coupling.
>
> What I use instead are three binocular cores stacked and wound with two
> passes on the primary and 4 passes on the secondary. 2:4 turns and a 16:1
> Z. According to W8JI there is only about 12pf of capacitance and it makes
> sense because of the reduced amount of secondary windings.
After some quiet time with paper, pen, and calculator - I think I got it
figured. I'm trying to go from 950 to 50 ohms, or 19:1, or 4.36:1 turns
ratio for a single BN-73-202 core. A 2 turn:9 turn winding comes pretty
close, and the 3 turn:13 turn comes real close. But you've indicated that
the interwinding capacitance may be too high
If I look at 2 cores stacked together (where the turns ratio varies as the
cube of the impedance ratio), I get a 2.67 turns ratio which works out
nearly perfectly to a 3 turn:8 turn winding with essentially no mismatch but
still with interwinding capacitance concerns (?).
If I look at 3 cores stacked together (where the turns ratio varies as the
quad of the impedance ratio), I get a 2.088 turns ratio wherein a 1 turn:2
turn winding or a 2 turn:4 turn winding both yield a close 16:1
transformation which is somewhat of a mismatch for 19:1, but has minimal
interwinding capacitance as many have stated.
My analysis of 4 stacked cores just looks like plain overkill - an academic
effort at best.
So which degrades the signal:noise ratio more on a flag/pennant? - some
mismatch in the impedance transformation or some interwinding capacitance?
If I've steered myself out of the pragmatic lane of the practicality highway
and I'm beginning to careen sideways in the theoratical median strip,
someone grab the wheel and set me on course.
> Steve KK7UV.
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