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Re: This phase shift stuff...

Hi,

I already have a 4.25 inch diameter x 26.125 inch coil with about 700+
turns of #24 on it.  This should be fine for such an experiment.  The
resonances you menation are well known but the phase differences along the
coil are the real question.  Is the phase going from 0 to 90 along the
lenth of the coil as would be the case in a 1/4 wave whip antenna. Or, is
the phase locked in sync as in the case of standing waves on a string
musical instrument?  A continous wave may develop large standing resonant
voltages that would not be realistic, but a number of 555 timers and some
gates should be able to give some pretty close pulses.  Even using a tuned
primary circuit (at low voltage) and an high frequency amplifier could
provide a very realisitic signal if experimentation shows the need...

	Terry


At 01:59 PM 2/18/99 -0800, you wrote:
>Tesla List wrote:
>
>>         A long thin secondary with no top load may be the best example
to be
>> studied.  I worry about a probe disturbing the fields around the coil and
>> causing false measurements.
>> A physically large coil will be less
>> susceptible to this however.  Fiber optic probes made for the task (small)
>> may have very negligable efects.  A continuous sine wave may not be the
>> signal of choice.  Perhaps a pulse generator or arbitrary signal generator
>> would be the best thing to use even though that is on of the few toys I
>> still don't have ;-(
>
>Some extra comments:
>There is no need for a long thin secondary. The effects appear in any
>form. I used a secondary with 12.5" of length and 3.5" of diameter.
>The excitation of the primary with shorted gap by a slow square wave
>current source allows extremely sensitive measurement of resonances,
>because perfect beats (observed over the low-impedance primary) 
>appear only at these frequencies, and they are practically not
>affected by losses (they decay faster as the frequency increases, of
>course). Losses cause the same measurements made with sine waves
>far less clear.
>I made the measurements using a simple 555 oscillator driving a
>current source made with two transistors in cascode configuration.
>No special signal generator was used.
>And note also this: There are high-order resonance modes in coils
>with large top loads too. It happens, however, that these modes
>"see" the large top capacitance as a practical short-circuit to
>ground, and put a voltage zero close to the top of the coil instead
>of a voltage maximum. The frequencies of these resonances are
>close to 2x, 4x, 6x, ... the main resonance frequency of the coil
>without top load.
>But do these high-order modes have influence in the operation of
>normal coils? Ideally no, but they can explain why some coils show 
>sparks along their lenght. If the primary is tuned to about twice the
>correct frequency, this can cause a voltage maximum close to the 
>middle of the secondary. Maybe sparks can also excite these modes.
>
>Antonio Carlos M. de Queiroz
>
>
References: