Re: RF ground - what if you can't use a ground rod?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 05:51 PM 6/28/2005, you wrote:
> Original poster: Ed Phillips <evp@xxxxxxxxxxx>
>
>
> 1. For efficiency at RF ground radials should be as long and as frequent
> as space and economics will permit.  As you point out, the point of
> diminishing returns is when they a somewhat longer than the antenna (or
> coil) height.  It's common in big antenna systems to have the radials in
> the form of a "counterpoise" mounted high enough that the electric field
> from the antenna doesn't encounter anything like grass, which can
> introduce significant losses.



Or, for that matter, the soil.   For a TC or an antenna, in both cases one 
would want to minimize the losses in the soil.


> 2. TC's are extremely lousy radiators and I doubt that the power loss
> due to radiation from any coil is significant compared to other circuit
> losses, particularly in the primary gap.  Loss in the streamers really
> represents loss in the desired output and, of course, doesn't count.
> Look up the charactistics of "Helical Radiators" in a communications
> handbook.  If their length is only a hundredth of a wavelength (say 5
> feet at 200 kHz) their radiation resistance is negligible (less than 32
> milliohms).

I suppose that I was making the point that the design goals for antenna 
counterpoises, groundplanes, radial systems, are very different from those 
for TCs.  Interestingly, TCs DO radiate fairly well at VHF frequencies, but 
I think that's mostly accidental, and there's not much power there, so 
radiative "losses" are neglible in any case.

> 3. The analogy between the ground plane and the plate of a capacitor is
> a good one, and pretty much tells the whole story.  I maintain that the
> ground plane should also be connected to a power ground for safety.

I forgot to mention that, but it is very, very important.



> Ed