Re: Tesla Coil RF interference 2

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

Original poster: "Antonio Carlos M. de Queiroz" <acmdq-at-uol-dot-com.br> 

Tesla list wrote:
 >
 > Original poster: "Gary Weaver" <gary350-at-earthlink-dot-net>
 >
 > Transmitters use to be Spark Gap type transmitters way back when.  The
 > Titanic had a spark gap transmitter as I recall.  I wonder if an LC circuit
 > could be attached to a TC spark gap and transmit on a certain frequency.  I
 > just did some calculations and I get 900 MHZ with 1pf cap and 3 turns of
 > .018 dia. wire .125" OD .250" long.  Wonder if a cell phone would pick that
 > up.  I might build an LC circuit on my TC for a certain radio frequency and
 > see if it will transmit to a radio.   I did a little research on spark gap
 > transmitters it seems to be only a spark gap connected to an LC circuit
 > with an antenna.   Simple technology.

The most primitive tuned spark transmitters were just an inductor
connected
to an antenna, with a spark gap to ground. A charging circuit across the
spark gap, much as used in Tesla coils, were used to charge the antenna
to high voltage. In this system, when the gap fires the antenna
discharges
through the inductor, causing oscillations that decay exponentially with
time. The inductor can be omitted, but then the oscillation frequency
and Q of the circuit is determined only by the antenna.
A simple vertical 900 MHz antenna (1/4 wave = 7.5 cm) with a spark gap
to
a ground plane below it would transmit significant power. Transmitters
at frequencies that are integer fractions of 900 MHz would too, because
an exponentially decaying sinusoid generates lots of harmonics, and
there are thousands of Volts at the antenna.

A Tesla coil configuration, where the antenna replaces the terminal at
the top of the secondary coil, allows much higher voltage at the
antenna,
and so much greater output power, at the cost of transmission at two
frequencies before the quenching of the primary gap, and at one after.
But the structure seems difficult to make for 900 MHz.

Antonio Carlos M. de Queiroz