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Re: Hello,

Tesla List wrote:
> 
> Subscriber: c604313-at-showme.missouri.edu Thu Jan 23 22:34:51 1997
> Date: Thu, 23 Jan 1997 16:01:24 -0600 (CST)
> From: c604313-at-showme.missouri.edu
> To: Tesla List <tesla-at-poodle.pupman-dot-com>
> Cc: Tesla-list-subscribers-at-poodle.pupman-dot-com
> Subject: Re:Hello,
> 
>      Hello Tesla builders,
>   Hi, my name is Bert Schumann from Columbia Mo.  This is my first e-mail
> to the group.  I'm glad a group like this exists and that it wasn't hard
> to find!  (Are there any other coilers in the mid missouri area???)
>     I've built several coils over the past 4 years, just small ones (300
> watts). And am in the process of trying to get a larger one up and running
> (700 watts)., but low and behold I seem to have a knack for blowing out
> neon xformers (at least I didn't blow out an entire power station like
> Tesla did at Colorado Springs!!)
>     Any way, I was woundering what would be the best way to test for
> resonant frequency in the secondary (Toriod included) if one had a
> variable function generator and o'scope available to use? I hear it is not
> such a good set up to just string a wire a couple of turns around the
> secondary and then hook it across the function generator with the o'scope
> placed on both the top and bottom of the secondary. The o'scope will
> actually change the resanant frequency some, but is this effect
> negligable? Is there a better way to test for Sec. Res. freq?
>     And what about the primary?  I was just planing on hooking all
> primary parts together in series with the function generator and o'scope
> (minus the sparkgap and xformer of course and probably throw in a
> resister in order to keep the function generator from strainin'.) I would
> then adjust the function generators frequency in order to find its max
> through put.  Is this a satisfactory set up?
>     Thanks,
>     --Bert S.

Bert,

Now the list has at least 3 Berts! The easiest way to test the resonant
frequency is to leave the secondary/toroid in-place inside the primary,
disconnect the earth ground from the bottom of the coil, and connect a
sine-wave signal generator through a pair of high-brightness LEDS (back-
to-back) to the base of the secondary:


                    LED's
  from           |--|<----|
 signal   -------|        |------  to base of secondary/toroid 
  gen.           |--->|---|


The signal generator should be capable of driving at least 4 V
Peak-to-peak. Slowly increase the frequency until you find the frequency
that gives you the most current (i.e., the brightest LED setting). This
will be the natural resonant frequency of the secondary/toroid pair
(Fo).

You can do a similar thing with the primary, only this time REMOVE the
secondary completely and put it into another room. Next, short the
sparkgap and connect the signal generator, through the LED's, across the
tank capacitor (power off, of course!). With the spark gap shorted,
you'll have the primary inductance in parallel with your tank cap. Now
carefully adjust the signal generator to find the point of minimum
current ("anti-resonance"). Adjust the coil tap until this is the same,
or slightly lower than, the secondary/toroid center frequency above.

Just for grins, since you've come this far, let's measure the coupling
coefficient (i.e., the portion of magnetic field lines that are common
to BOTH the primary and secondary). Leaving your signal generator
connected as before to the primary with the sparkgap shorted out, put
the secondary/toroid back into the center of the primary and connect the
RF earth-ground to the base of the secondary coil. Now adjust the signal
generator to measure the two points of lowest current - these should be
approximately centered around the previous primary and secondary
frequency. The greater the seperation between the lower and upper
"sideband" frequencies, the greater the degree of magnetic coupling
between the primary and secondary coil. Assume you measure sideband
frequencies Flow and Fhigh. The coupling coefficient, "k", can now be
found as:

       k = (Fhigh - Flow)/Fo

Certain values of "k" will tend to cause better operation, with 0.153,
0.18 or 0.22 being a few of the "magic" values.

Hope this helps!

Safe coilin' to ya', Bert!

-- Bert --