TC Resonance and Topload Measurements

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

Original poster: "Kevin Ottalini by way of Terry Fritz <twftesla-at-uswest-dot-net>" <ottalini-at-mindspring-dot-com>

All:
	I just completed a small coil setup specifically
to test resonance with and without a topload, and coupling
between primary and secondary.

Rather than use the 60Hz high-current method that Terry,
et. al. have been using for the ACMI testing, I instead
used my Tek Oscilloscope and B&K function generator to
check behavior at 60Hz as well as at higher frequencies.

Although it was my intent to verify the 60Hz behavior, I
found that I was unable to get any significant coupling
with a 60Hz sinewave running at 1Vpp and at 10Vpp what I
saw could only be regarded as 60Hz patterned noise.

(My apologies Terry!)

However, after sweeping the coil from 30Hz up to 20MHz,
I found only one peak at 927.3KHz. I adjusted the primary
up and down the secondary to maximize the output,
and then moved wires and the entire setup until there were
no significant influences from test equipment or wires or
tables, etc. then I re-adjusted the input to exactly 1.00Vpp.

At this point, all influences (hands, wires, etc.) had the
universal effect of lowering the resonant frequency, never
raising it.

With exactly 1.00Vpp sinewave input (verified sine with
no obvious distortion), I was getting approximately 48Vpp
output into a 9pf, 10Mohm scope probe.

I then added a small 12" diameter smooth aluminum toroid
to the top and found that the resonant peak had moved down
to 642.5KHz. The output was now running about 40Vpp.

I then removed the toroid and added a Jennings variable
vacuum capacitor (10pf to 900pf) from the top winding to
ground and adjusted it until I got a peak at 642.5KHz.

I then measured the capacitor with my B&K precision
capacitance meter (good to 0.1pf).  The matching value
I measured was 15.9pf.

I then went back to a no-topload setup (back to 927KHz)
and raised the secondary until I saw a significant drop
in output (~52%).  At this point (25Vpp output) the
bottom secondary winding was 1.25 inches above the
topmost primary winding.

One observation here is that the Peak-to-Peak output
voltage seen in the max coupled position is close to
the Ls/Lp ratio of 51 (p-p ratio not RMS).

Another important observation here is that once everything
was "tuned", the system was reasonably insensitive to the
setup placement height above ground and proximity of test
equipment and wires.

Here are the coil specs:
========================
Primary:
--------
        Diameter:  6.00 inches (uniform coaxial)
           Turns: 13.00
          Height:  1.75 inches (uniform coaxial)
            Wire: 12 gauge solid copper PVC insulated, tight wound
      Inductance: 35.4uH (1KHz) Minimal coupling position
      Inductance: 35.6uH (1KHz) Maximum coupling position
*   Solenoid Est: 34.2uH (L(uh) = R^2 * N^2 / 9R + 10H)
      Resistance:  0.100 ohms (120Hz)

Secondary:
----------
        Diameter: 3.5" PolyCarbonate Coilform, spiral grooved
   Circumference: 11.0" verified exactly in the groove.
           Turns: 270.0
             TPI:  27.0
          Length:  10.0 Inches of turns (12 inches overall)
            Wire:  22 gauge magnet wire
      Inductance:  1.801 mH (1KHz) Minimal coupling position
      Inductance:  1.809 mH (1KHz) Maximum coupling position
*    Wheeler Est:  1.900 mH
      Resistance:  4.462 ohms (120Hz)
*   Medhurst Est:  5.2pf (self capacitance)
*  Resonance Est:  960.0 KHz unloaded and 660.0 KHz loaded (15.9pf)
Actual Resonance:  927.3 KHz unloaded and 642.5 KHz loaded (15.9pf)

Minimum coupling height: 1.25 inches above top winding of primary.
Maximum coupling height: primary situated 3.5" to 5.25" up from
                         bottom of secondary.

Smooth Aluminum Toroid:
-----------------------
            Diameter:  12.0"  (3"x6"x3")
     Capacitance Est:  13.3 pf (Bert Pool)
Capacitance Measured:  15.9 pf

Test Equipment:
---------------
       Oscilloscope: Tektronics 2215 (60MHz) 10Mohm, 9.0pf probe
 Function Generator: B&K 4040 (20MHz)
Universal LCR Meter: B&K 878
  Capacitance Meter: B&K 810B

(Hmmm ... someone might think I owned stock in B&K!)

Best,
	Kevin

*---------------------------*
* Kevin Ottalini            *
* High Voltage with Style!  *
* ottalini-at-mindspring-dot-com   *
*---------------------------*