Re: slow-wave helical resonator

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Gary,

On 16 Aug 2002, at 23:01, Tesla list wrote:

> Original poster: "Gary Peterson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <glpeterson-at-tfcbooks-dot-com>
> 
> > . . . The 17% in-coil velocity is a little quick.  A typical TC
> > secondary would have a so-called velocity factor more like 0.1%,
> > compared with 95% for an open wire and perhaps some 10%-90% for
> > a helical antenna.
> 
> Thanks much for the great info.  I've modified the glossary entry
> accordingly.
> 
> > For magnifier operation, the extra coil combined with the secondary
> > must have a total electrical length of 1/4 wave. . . .
> 
> For maximum spark length this may be true.  However, for a magnifying
> transmitter the tuning is different.  Here are Tesla's instructions from the
> July 24, 1899 C/S diary entry:
> 
> ". . . the excited [extra] coil must be such as to vibrate in accord with
> the secondary or (inasmuch as the secondary vibration is affected by the
> primary) the free vibration of the excited coil must be the same as that of
> the combined primary and secondary system.  When the vibration in the
> secondary is exactly the same as the free vibration of the excited coil the
> maximum rise will be obtained on the coil, in any event, but for the best
> result the secondary must also be tuned to the primary so that greatest
> impressed e.m.f. is secured on the coil.
> 
> "In cases where the secondary is in such intimate inductive connection with
> the primary then the latter condition need not be considered and it is only
> necessary to adjust the coil so that it will have the same period as the
> oscillation in the secondary.  In fact, I believe this will be, in the end,
> the best condition in practice for, if the transformer be efficient, the
> connection between the primary and secondary must be a very close one.  In
> such a case the high impressed e.m.f. on the excited coil will be obtained
> only by transformation and not by resonant rise."
> 
> That is to say, first increase your power supply voltage by transformer
> action with a 'master oscillator,' then use it to drive a 1/4-wave helical
> resonator.
> 
> Gary

It took about five minutes with an oscilloscope to find out that this 
recipe doesn't work for anything. In treating the pri-sec system as a 
master oscillator, the assumption is made that the primary is driven 
by a voltage source and that the pri-sec behaves like a voltage 
source. Unfortunately, neither is true. The primary is driven by a 
charged capacitor which runs down as energy is transferred, and 
coupling constant between primary and secondary of less than 1 or 
close to it also causes the system to deviate from the properties of 
a voltage source.

Regards,
malcolm