RE: measuring the resonant frequency of the secondary

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

On 20 Jul 2004, at 8:14, Tesla list wrote:

 > Original poster: "Steve Conner" <steve.conner-at-optosci-dot-com>
 >
 >  >You have to use a signal generator with very low output impedance to
 >  >see the peaks cleary.
 >
 > To check the tuning of a complete TC (primary and secondary together)
 > I like to use a ferrite transformer to couple the output of the sig
 > gen to the primary. I connect the sig gen to a 30 turn winding on a
 > ferrite ring, and drive the TC tank circuit from a single turn
 > secondary (an alligator clip lead passed once through the ferrite
 > ring, and hooked across the TC spark gap)
 >
 > This works great with an old HP 200 style tube oscillator- these have
 > a generous output of ~40V into 600 ohms. It actually excites the TC
 > enough that I can pick up the secondary output from a scope probe held
 > in mid-air about 2ft away, and see the resonant frequencies that way.
 > I can also see the oscillator's output voltage being loaded down at
 > the resonances.
 >
 > To test the secondary alone, you can base drive it directly from the
 > oscillator (connect one lug of the oscillator output to the secondary
 > base, and the other to a groundplane, or the AC line ground.)

It is important when doing this for measurements of a scientific
nature that the generator presents as low a source impedance as
possible. A 600 Ohm source will seriously degrade the Q of a
resonator with an ESR of a couple of hundred Ohms. I think you should
still be using your drive transformer if this is what you are
intending to do. The generator I use has a defined 0.5 Ohm output
impedance together with overcurrent (limiting) indicator so I know
when the source impedance is deviating from its ideal.

Malcolm