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Adjacent-spiral-primary test

Original poster: "K. C. Herrick" <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 77 KHz with 2.8 V across the LC, "in".
    2.  Fr of 83 KHz with 2.4 V across the LC, "out".  Fr, 7% higher.
C. With the two spirals going in opposite directions and with one inner end connected to the other outer end: 
    1.  Fr of 157 KHz with 0.63 V across the LC, "in".  Fr, 28% higher.
    2.  Fr of 123 KHZ with 1.2 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 253 KHz with 0.22 V across the LC, "in".  Fr, 22% higher.
    2.  Fr of 207 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