Re: Tesla Coil RF Transmitter

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Bob (R.A.) Jones" <a1accounting@xxxxxxxxxxxxx>


Hi Jim,

> Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>
>
> At 10:51 AM 9/18/2005, Tesla list wrote:
> >Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
> >
> >Hi Jim,
> >
> >Is another differentiator between near and far fields is where the
> >wave impedance becomes 377 (impedance of free space, iirc) ohms???
>
> The wave impedance is everywhere 377 ohms, independent of whether you
> are in the reactive near field or radiating far field.  All that
> impedance tells you is the relative strength of the E and H fields of
> a "propagating" EM wave.  If I set up a nifty magnetic probe and an
> electric probe in the same location with all manner of waves rushing
> by, the V/m should be 377 (more properly 120 pi) times the A/m at
> that location.

Thats correct if all the waves are going by in one direction.

>
> In the reactive near field, this isn't necessarily the case (or maybe
> it is.. I'll have to think about it), because you can have fields

It is similar the characteristic impedance of a transmission line or a Tesla
coil. Some times referred to as the wave impedance.
But if you measure the ratio of V and I along a shorted or open transmission
line it can be very different than the characteristic impedance.
This is caused by the summation of the forward and  reflected wave i.e. a
standing wave. The ration of the voltage and current (and phase) vary along
the line.
Similarly the near field is a supposition of waves. Hence if you measure the
ratio you may not get the usual wave impedance.
There is only one set of Maxwell's equations and all space including that
next to a dipole/conductor obey them.

Robert (R. A.) Jones
A1 Accounting, Inc., Fl
407 649 6400