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Re: Spark Gap Oscillator Efficiency

Tesla List wrote:
> 
> Original Poster: "Steve Young" <youngs-at-konnections-dot-com>
> 
> Coilers,
> 
> I have wondered just how efficient a disruptive TC is in converting input
> power to RF power. 
> Has anyone done this, or otherwise measured the efficiency?  How does
> disruptive TC coil efficiency compare to tube coil efficiency?  Seems like
> I remember a Class C RF amplifier is around 70% efficient.

A spark gap excited resonant circuit is actually a pretty efficient way
to generate RF, if (and only if) you don't care about the spectral
characteristics. The RF power is spread over a wide band and isn't
uniformly distributed. If you get the Q of your primary up high enough,
it becomes more efficient, and the spectral purity is better.

However, if you look at DC power in to RF power out IN A SMALL BANDWIDTH
the tube circuit is much better, and, what is more important for
practical use in the RF world, it is more consistent and controllable
(i.e. you can modulate it more easily).

A class C amplfier is almost the same as a spark gap LC circuit. The
tube is acting like a switch, putting periodic pulses into a resonant
circuit. Because the tube is a switch, and not acting as a linear
amplifier, the losses in the tube are low (it is either all the way on,
or all the way off, and spends little time in between). The spark gap is
the same.

WHen you need a linear amplfier, which is what most RF amplifiers are
these days ( Nobody except for hobby types broadcast in morse code or AM
anymore (even commercial AM is really independent sideband and needs a
linear amp)(except television, but that is a different story)), you have
to go to class B or AB, and the efficiency drops way off (although,
there are lots of schemes to gang up multiple efficient class C amps to
make a quasi linear amp)

All in all though, a spark gap and a tuned circuit is a pretty efficient
way to generate RF power.


-- 
Jim Lux                               Jet Propulsion Laboratory
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