Original poster: "K. C. Herrick" <mailto:kchdlh@xxxxxxx><kchdlh@xxxxxxx>
I prevail on Terry to post
<http://hot-streamer.com/temp/SPIRALS_IN.JPG>http://hot-streamer.com/temp/SPIRALS_IN.JPG
and
<http://hot-streamer.com/temp/SPIRALS_OUT.JPG>http://hot-streamer.com/temp/SPIRALS_OUT.JPG
As I've noted, I made the spirals from 2-side p-c stock; they're
about 10.5" in outside diameter. One is permanently held positioned
"out" and the other can be moved "in" or "out". The outer rims (of
copper) are cut (both sides!) so they don't constitute shorted turns.
I set them up for parallel resonance with 270 nF of capacitance,
then that resonant element in series with 470 ohms, connecting to a
sine-wave generator having 50 ohm output impedance. I connected a
scope (1 meg input resistance and via about 2 ft. of coax lead of
unknown Z) and a frequency-counter across the resonant element. (I
should have connected the counter directly to the sig gen, but I
found that made no difference.)
Here's what I measured with 20 V p-p from the sig gen in each case:
A. One spiral only, with the other one positioned "out":
Fr of 142 KHz with 1.1 V across the LC.
B. With the two spirals going in opposite directions and with the
inner ends connected (i.e. as if they constituted a conventional
multi-turn coil):
1. Fr of 79 KHz with 2.5 V across the LC, "in".
2. Fr of 86 KHz with 2.5 V across the LC, "out". Fr, 9% higher.
C. With the two spirals going in opposite directions and with one
inner end connected to the other outer end:
1. Fr of 191 KHz with 0.5 V across the LC, "in". Fr, 53% higher.
2. Fr of 125 KHZ with 1.35 V across the LC, "out".
D. With the two spirals going in the same direction and with the
inner ends connected,:
1. Fr of 170 KHz with 0.54 V across the LC, "in". Fr, 35% higher.
2. Fr of 126 KHz with 1.2 V across the LC, "out".
E. With the two spirals going in the same direction and with one
inner end connected to the other outer end:
1. Fr of 82 KHz with 2.7 V across the LC, "in".
2. Fr of 90 KHz with 2.3 V across the LC, "out". Fr, 10% higher.
F With the two spirals going in the same direction and with inner
ends tied and outer ends tied (i.e., paralleled):
1. Fr of 153 KHz with 1 V across the LC, "in".
2. Fr of 167 KHZ with 0.8 V across the LC, "out". Fr, 9% higher.
G. With the two spirals going in opposite directions and with inner
ends tied and outer ends tied:
1. Fr of 248 KHz with 0.16 V across the LC, "in". Fr, 20% higher.
2. Fr of 206 KHz with 0,4 V across the LC, "out".
Very interesting... Looks as if cases B & E are the only decent
ones--with a resonant impedance that stays much the same and
relatively high and with a (modest) 7-10% frequency change. And
they are essentially identical cases since the magnetic fluxes from
the two spirals are in both cases additive.
I don't think I'm too much impressed with this scheme.
Comments?...
KCH