[Lowfer] Measuring high Q

Ed Phillips [email protected]
Fri, 21 Nov 2003 10:04:03 -0800


Dave Brown wrote:
> 
> What sort of Q values do you typically get  for the Tesla coil secondaries
> Ed? Obviously they will be high, but I wonder just how high?  Hope to find
> out for myself sometime- I have a couple of old neon xfmrs here somewhere
> just waiting for that magic day when I have nothing else to do!!
> Dave
> ZL3FJ

	For the small coils I've measured the Q isn't very high.  Not
surprising considering their lousy shape.  Typical measurement on a
small coil which gives ~27" streamers when running from a 12 kV, 60 ma
transformer at about 400 watts measured input:

"
COIL WOUND 11/12/95:
FORM: CARDBOARD TUBE, HEAVILY SHELLAC COATED.
COIL HEAVILY COATED WITH URETHANE VARNISH
DIAMETER: 3.07"
LENGTH: 16.16"
WIRE SIZE: #28 B&S
N calculated: 1131 TURNS (from geometry, 1 kc inductance)
L 1kc: 17.37 mH
Q 1kc: 1.82
UNLOADED:
	fr: about 490 kc (490.7 in basement 11/23/95)
	*f 3dB (unloaded): 3 kc
	Q: 163 (very approximate)
	Cd: 6.06 uufd (calculated from fr)
	Ccalc: 6.16 uufd (Medhurst)
LOADED BIG TOROID:
	fr : 332.7 kc
	*f 3dB: 1.6 kc or less (approximate, hard to measure)
	Q: 208 (very approximate)
	Cd: 13.33 uufd (calculated from fr)
	Ctoroid: 7.27 uufd"

	Because of the low streamer impedance the actual operating Q's under
"breakout" conditions must be much lower.  It's never been obvious to me
why guys worry so much about unloaded secondary Q.

Ed