Re: Power output

["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: "Alexander Rice by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <alex-at-rices.myip-dot-org>
> 
> >       So.  How COULD the _power_ be measured?
> >       Sort of need to do it pre breakout, which
> may be of
> >       no interest.  What kind of
> instrumentation?
> >       An interesting complement to the
> discussion of gap losses.
> >
> >       (best i can think of, post break out, is
> some sort of bizarre,
> >       huge, calorimeter.  Not Practical...)
> >
> >       best
> >       dwp
> 
> Maybee a better method might be to measure
> everything that is NOT going into the
> streamers, for a start you could measure gap
> losses calorifically without too much
> dificulty, you cam amke a pretty good
> guestimate of cap losses, a lot to peole have
> meen modelling e-fields so we should be able
> to figure out how much of the energy is being
> radiated. Then measure input power, taking
> into account transformer losses and presumably
> what is left must be useful power out. This
> would be much easier with a coil like thor
> that is heavily instrumented. Althought this
> would be rather laborious it is more practiacl
> than trying to masure output directly.
> 
> Just a (less than original) idea
> 
> Alex

	Direct measurement is probably impossible.  To that list I'd add
inductor losses which are probably equal to or bigger than the gap
loss.  Because all of our coils are very short compared to a wavelength,
radiation loss is so small that it's not worth calculating. (Formulae
for radiation properties of short helical vertical antennas can be found
in many handbooks.  Bottom line is that electrically short antennas are
very lousy and inefficient radiators.)

	It used to be common to determine ("measure") the power output of large
transmitters by an approach essentially identical to that which you
suggest.  The DC power input was easy to measure, the circuit losses
could be calculated from known circuit parameters, and the loss in the
amplifier tube(s) was measured by observing the temperature of their
plates.  Running the tubes on measured DC with that gave the same
temperature permitted estimation of the power loss (plate dissipation)
and the net output power was the input power less all of the losses. 
This method is probably about as good as any, even today, if the
measurements are made carefully and the instruments are well calibrated.

	REcognize one thing, though.  TC's aren't very efficient devices.

Ed