Re: Radial Horizontal Ground Rods (RHGRs :-)

From: 	Jim Lux[SMTP:jimlux-at-earthlink-dot-net]
Sent: 	Friday, December 12, 1997 10:38 AM
To: 	Tesla List
Subject: 	Re: Radial Horizontal Ground Rods (RHGRs :-)

> From: 	Sulaiman Abdullah[SMTP:sulabd-at-hotmail-dot-com]
> Sent: 	Friday, December 12, 1997 6:00 AM
> To: 	tesla-at-pupman-dot-com
> Subject: 	Re: Radial Horizontal Ground Rods (RHGRs :-)
> Greetings, I suspect the "best" horizontal grounding would be as if
> you were building an r.f. transmitter, i.e. the horizontal elements
> should be 1/4 wavelength long, the same as the length of wire used to
> wind your secondary coil. (or as long as possible if not achievable)
> Sulaiman. 

Actually, I wouldn't think that 1/4 is optimum. 1/4 is good if you are
creating suspended radials below a 1/4 vertical antenna to reduce radiation
resistance. Also, at 300 kHz, that 1/4 wave radial will be 250 meters long,
unlikely to fit in the average back yard. There are various schemes for
creating physically short but electrically long radials, like helical
loading (just like the tesla secondary), but they are lossy.

Go back to why you want the ground. If it is there to work the capacitance
of the top load against and to provide an even field distribution, then
some chicken wire or reinforcing mesh (4x4" mesh for concrete) laid out in
a circle diameter at least 3-4 times the height of the top of the secondary
should work. If you really wanted to spend some money, you could go buy
many square meters of copper flashing.... various types of perforated metal
decking are also available.

You do want a low RF impedance for this sort of application, so braid isn't
particularly great. Try the mesh, chicken wire (aka aviary netting ) is
cheap, it rolls up when you are done, etc. It has lots of parallel
conductors so the impedance is fairly low. BTW chicken wire is lousy for
shielding, though, because the wires are woven and signals can propagate
from one side to the other through the holes.

For a really off the wall scheme, how about hosing the area down with a
salt solution. If you pick a suitable salt, you can fertilize the lawn at
the same time as increasing the surface conductivity. Or, if you want that
scorched-earth post-apocalyptic look that is so trendy now, use ordinary
table salt.