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A tuning procedure, and 2 meters.
I tried a couple of things today, and would like to explain the tuning
procedure that I have found works for me. Correct me if I`m wrong.
I know tha ballpark figure of the resonance is 100kHz.
I measure it this way: Connect the signal generator to the base of the
coil via a 1kohm resistor. Connect the ground of the scope and the
signal generator. And connect the probe of the scope to a small piece of
wire suspended from a stick in the dirt 1 metre away. Pick up a signal
and tune the generator for max signal and then read the frequency with
fluke 87.
If I do this with the secondary system standing alone, I get 98kHz.
However, if I do it with the secondary system mounted in the operating
position, (and the cap disconnected) I get 103,2kHz.
After this, I measure the primary resonance, with the signal generator
via a 47kohm resistor, and scope probe to one side of cap, grounds to
the other side of cap, gap shorted. Find tapping point that results in
resonance at 98 kHz, and write it on the primary coil. Then proceed to
write the res. freq. every 1/8 turn, untill beyond 104 kHz.
Thanks to Bert, who has a coil similar to mine, I was advised to start
at a frequency 1,5 kHz lower than the secondary freq.
I found that a good tune was established at a primary resonant frequency
of 100,6 kHz, 2,6 kHz lower than the secondary`s, as measured _in situ_.
I would be interested in knowing if others have come to the same
conclution, that it is the "in situ" frequency of the secondary, that
matters?
Or do you tune by ear? Frankly, I let the ears decide the final point,
when the whole system attained a nice, coherent, sizzeling crispness in
sound.
Anyway, It cannot be far off, because when I opened the gaps to 1/2 ",
the streamers got bigger than before, and I recorded a record 6'8" to
the grounded rod. This figure means a lot to me, as it is 2 meters.
After that I tried the trick from Bert Pool, putting small omega shaped
tapepieces on the toroid, and I think it is a nice trick, Thanks!
putting 4 equispaced tags on, a bit above equator, resulted in 3
simultaneus streamers moving randomly around between the four tags. Very
pretty, although one produced the first hit to the strike-rail in my
short career. Boy, do those long streamers move around a lot.
I have absolutely no idea what power level I`m running, because even
though I just installed 60µF of PFC`s, the amperemeter is locked against
the 30 amps stop. This is btwn. 2 phases at 400 volts. But I have 16
amps fuses, so there is no way, that this figure can have merit. How do
I measure the power?
The MMC is still holding up, and I think this means that the consept is
valid for medium-powered coils.
Cheers, Finn