Re: Tesla simulations vs. scope traces (fwd)
From: Antonio Carlos M. de Queiroz[SMTP:acmq-at-compuland-dot-com.br]
Sent: Sunday, December 21, 1997 11:49 PM
To: Tesla List
Subject: Re: Tesla simulations vs. scope traces (fwd)
Tesla List wrote:
> 1) With a digital scope (500mhz) I captured some traces of my 8X6 coil
> operating and ran the output through a FFT program at work. The scope was
> triggering on a 4MHz ring-up , followed by a 100KHz sine wave.
Be very careful with digital scopes, specially when analyzing noisy signals (and
the vicinities of a Tesla coils are certainly very noisy).
They like to "invent" signals...
> 4) A distributed ladder network of series inductors simulating the bottom of
> the coil equal to the total secondary inductance/2 then /4 ,/8, etc..with
> capacitances to ground starting at the top equal to total secondary self-
> C/2+Toroid-C then self-C/4,/8, etc...showed a 91.58KHz component for the
> Inductor L7 at the top of the coil, and also 1,2,3,and 4MHz spikes for the
> Inductor L1 at the bottom of the coil...simillar to the scope traces from the
> real coil.
I looked at the model at your site and repeated the analysis with another
program. That circuit really shows a set of very high Q resonances above 1 MHz, as
your analysis showed. The problem is that the model is wrong. The inter-winding
capacitances should be connected across the R-L-R sections, not to the ground.
Also, the value of the first capacitor should be 0.140625 pF and the last inductor
should be 0.578125 mH.
With this all the sections resonate at the same frequency, and the circuit
reduces to a single section (this is why inductors with distributed capacitances
and resistances can be considered as simple LC tanks).
The transfer function to the output shows a high peak at 121 kHz and a notch
at 2.15 MHz. Nothing more.
It is true that nonlinearities (spark gap, sparks) in the primary and secondary
circuits can generate other frequency components than those of the usual resonances,
but this is not considered in this analysis.
Antonio Carlos M. de Queiroz