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Primary Qs
Hi everyone,
After some discussion on this subject and (as usual)
some misgivings about past measurements, I decided to take some
more to check. A resistance of about 150kOhms was used in series
with the DC supply. Measurements were taken using 2 coils and 2
capacitors. A 50Hz bandstop filter was used to block stray mains
waveforms from the scope front end.
Circuits : 11.8uH/100nF 350uH/100nF 350uH/25nF
Fr : 144.6kHz 27.15kHz 38.5kHz
Q (3dB) : 35 54 64
Poor isolation shows itself. Capacitor quality is not great either.
Measurements were then taken at 4 different voltages for each
combination:
Cap Voltage 3kV 6kV 9kV 12kV
11.8uH/100nF (Q) 8.2 10.8 10.9 11.5
350uH/100nF " 11.5 13.7 13.6 14.4
350uH/25nF " 10.1 13.0 14.4 14.4
Max number of rings before gap extinguished : 32 for 350uH/25nF -at- 12kV
Min " : 15.5 for 11.8uH/100nF -at- 3kV
Q does trend up with increased gap current showing a drop in gap
resistance. It would be useful to get readings for much higher
voltages but the supply and caps on hand wouldn't allow it.
More interesting stuff: Gap at 12kV = 0.16" (160 mils), (4.07mm)
This translates to 75kV/inch on a linear basis but there would
be few if any "stepped leaders" from these electrodes :)
Gap electrodes are 1/2" diameter rounded tungsten carbide tips.
It would probably fire a couple of kV higher if a fast rising
waveform was used based on past experience.
The gap _always_ extinguished on a waveform peak (when Ip = 0)
As Greg said, the gap does look better than it has a right to. The Q's
are generally disappointing though. From the lowest L/C combination
at 3kV to the best at 12kV, there is less than a doubling of Q.
I guess the recipe is : high L/C ratio at a high voltage for lowest
losses. There is hope yet.
Malcolm