Re: slow-wave helical resonator

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

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