Re: Tesla Coil RF Transmitter

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Antonio Carlos M. de Queiroz" <acmdq@xxxxxxxxxx>

Tesla list wrote:
> Original poster: "Gary Peterson" <gary@xxxxxxxxxxxx>

> > MIT has a couple of very cool antenna animations which demonstrate
> > part of the idea that short antennas aren't necessarily "short":
> >
> > quarter-wave antenna animation, 2megs
> > http:/web.mit.edu/8.02t/www/802TEAL3D/visualizations/light/QuarterWaveAntenna/QuarterWaveAntenna.htm 
> >
> > short antenna animation, 2megs
> > http:/web.mit.edu/8.02t/www/802TEAL3D/visualizations/light/dipoleRadiationReversing/DipoleRadiationReversing.htm 
> The caption associated with the second animation doesn't say 
> anything about the antenna being electrically short.  It looks to me 
> like the thing is just drawn to a smaller scale than 
> previously.  Also, these animations represent the operation of a 
> dipole "antenna" (in the sense used above) in free space. This is an 
> inaccurate representation of the launching structure of a Tesla-coil 
> transmitter, which is grounded and by my definition is NOT an "antenna."

The pattern of a grounded antenna is just one half of the pattern of
a dipole antenna, with some distortion due to the nonzero resistance
of the ground. The high reactance of the short antenna can be recognized
in the animations by the electric field lines that form loops that grow
and then return to the antenna instead of detaching and forming
electromagnetic waves. Note that a similar animation appears in Maxwell's
book, so this is nothing new.

Antonio Carlos M. de Queiroz