Re: SSTC As a transmitter.

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

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<jimlux-at-earthlink-dot-net>
> 
> >
> > > a vertical conducting rod extending about 1800 feet above the
> > > earth's surface and excited at a frequency of 136 kHz would be
> > > a fairly efficient radiator.
> >
> > Certainly would.
> >
> > > a much shorter Tesla-type transmitting structure, say, about 50'
> > > overall height... would not be as efficient a radiator.
> >
> > Indeed.  

	It would be only 0.0069 wavelengths long!!!!!!!!!

> Actually, as far as radiating power uniformly in all directions (i.e. an
> isotropic radiator) goes, they're equally good. What DOES change is the
> various losses. The physically small radiator will have a low radiation
> resistance, implying high currents, which makes the power loss due to the
> inevitable resistance in physical structures greater (quickly... I^2*R adds
> up fast). If you could build your antenna out of superconductors, it would
> make no difference (for transmitting... receiving is another story).
> 
> The other practical side effect is that the impedance of a full size antenna
> varies less as a function of frequency than a small radiator, making the
> small radiator tougher to drive with a good impedance match (with mismatch
> also resulting in loss)... The large reactive component also contributes to
> loss from the circulating currents in the resistive components.
 
	Tesla's "radiator" was so small a fraction of a wavelength at any
frequency he proposed that this effect would be magnified to
unbelievable levels!  An even more serious problem is that the bandwidth
of the tuned circuits is exceedingly small when the operating Q is high
enough to minimize losses.  Since the transformation ratio varies with
the Q, which in turn varies with the power being drawn, it's hard to see
how the setup could ever be practical.  On top of all of that, the
resonant frequency is a function of the capacitance loading on the
secondary, which in turn is a function of the "conducting layer" which
Tesla proposed to use for one leg of his transmission circuits.  That
height varies by as much as 2:1 from day to night, and under differing
solar flux.  Since Tesla was intimately familiar with the application of
resonance, it's puzzling that he never mentions the tuning problem in
any of his publications.

	I've run some simple calculations based on determing the reactive power
which would be involved in the capacitance at reasonable "conducting"
layer heights and they indicate that operating Q's in excess of 10^7
would be required to achieve the losses he mentions.  At an operating
frequency of 100 kHz that would mean an effective bandwidth of about
0.01 Hz, and a required tuning accuracy of about a part in 10^8.  I
can't imagine how that would ever be possible.

> As always though,
> bandwidth gets narrower, and resistive losses increase.  But, for low
> frequencies, atmospheric noise dominates, so giving up some capture area is
> probably not a big deal, for communications, but of course, complete fouls
> up the power transmission aspect.

	Unescapable law of nature!

Ed