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RF GROUNDING

Quoting Marcus Young <marcusy-at-ozemail-dot-com.au>

The conversation worked it's way around to RF grounds and ground
pathing...

> Also, should I then replace the braided ground wire for my 
> secondary with something solid or stranded? (Chip)

  > The lowest resistance conductor you can find is best! 
  > Also as short a run of the conductor as possible.

Agreed!

  > I will use an 8 foot earth rod directly underneath the         
  > secondary. The base of L2 will be literally soldered to the    
  > earth rod. I reccomend drilling a hole in the garage
  > floor, and hammering that sucker as deep as you can....just    
  > where you want it!  :)  Just ideas.........

A single 8 foot earthed rod is woefully insufficient for a 5 kVA
Tesla setup....

BEGIN IMPORTED TEXT

             RF GROUNDING FOR TESLA COILS

I get a lot of questions about safety, radio and TV interference, 
performance, and tuning problems in reference to Tesla coiling.
Nearly every one of these areas is affected by the quaility
and proper use of a dedicated RF grounding system.

A small coil can fire off a radiating counterpoise (insulated metal 
plate) a few feet square. But when you overload a counterpoise, you 
get a really wicked corona display around the counterpoise, and the 
coil will produce no additional spark at the discharger. Having set 
up various experiments to study this effect, including tracing the 
ground current, and using a current transformer to measure the RMS 
amps coming from the base of a Tesla secondary, I can tell you this.

There is no such thing as a RF "system" ground that is too heavy.

                   Not in Tesla coils!

This is another thing that Tesla went on and on about. But my
follow up experiments in this area, which have been quite
extensive, show that he knew what he was talking about.

I got extremely lucky in that I had a hydraulic car lift in our
back driveway. This consisted of a 5' steel cylinder 14" in diam..
In addition to the giant piston, there are buried oil and air
tanks with all of the associated plumbing. The lift controls are
sunk right where the house foundation drains, and it is in the
lowest spot in rear of the house. There are no electrical
connections made to this lift, air being supplied when needed by
a hose. This was my Tesla ground.

A good Tesla RF ground is usually developed, not happened upon.
It will require some digging and post driving. It needs to be
kept moist. Drive deep with copper pipe, or copper clad rod, and
keep adding to it. Metal culverts, metal sewer drain pipe should
be connected if available. Spread out! Do not drive rod or pipe
close together. Four or five 8' rods driven in a long row, or in a 
"cross" pattern with posts set 8' apart will work. A ground that 
you are absolutely sure will ground a bolt of natural lightning, 
will be heavy enough to ground most coils. DON'T CHINCH!

People have asked me if I get complaints about RFI. The answer is
no. The reason is that I isolate my coil (system) ground from the
copper water pipe and from the utility ground (which in my house
are the same). Here is a basic list of things that you DO NOT
CONNECT to the system RF ground: WATER PIPE, GAS PIPE, UTILITY
GROUND, ANYTHING THAT STICKS UP IN THE AIR (fences, gutters,
downspouts) TELEPHONE GROUNDS, & CABLE GROUNDS. Most anything
else is fair game, but use common sense.

You build or find a heavy ground and you ground your coil system
to it. The connections made to this RF ground are as follows:
SECONDARY COIL, SAFETY GAP, STEP UP XFRMR CORE, BYPASS CAPACITORS
(if using a center tap grnd xfrmr), SPARK GAP MOTOR HOUSINGS,
SPARK SHIELDS, AND ANY OBJECT SUBJECT TO BE STRUCK WITH DISCHARGE

I don't usually use my caps lock, but this is important. This
technique prevents RFI complaints, and will save valuable
electronic equipment in your area from destruction. It may save
you from the last shock of your life.

You ground your variac housing to your neutral wire. All other
coil controls, relay housings, control xfrmr cores, line RFI
filters (run backwards) are grounded to the variac housing. Strap
is taken from the variac housing to a well grounded water pipe.
This protects the coil operator and the control circuits from
kickback that may come down the line from the step up xfrmr.

Two 60 cycle cables are run from the variac, through reversed
line filters, out to the step up xfrmr. No ground connection is
made anywhere between the 60 cycle cabinet ground and the RF
system ground. Hot wires only are given to the primary of the
step up xfrmr, as well as any gap motors or other utility for the
coil tank circuit.

This is called the "two ground system" and it is highly recom-
mended. The idea of the two ground system is to send all of the
RF to a dedicated ground, and prevent bleedover into your house
wiring, control cabinet and/or water pipe. It also protects the
operator with two low potential grounds from the lethal possi-
bilities of a coil misfire or similar "incident".

People have told me I am crazy for messing with all of this HV.
I take NO CHANCES with my ground. The ground strap is literally
the "bottom line" in coil safety or any other HV apparatus. If an
accident occurs; a core shorts out, a capacitor blows, or the
secondary decides to dump a 10' spark back to the tank circuit;
I know my safety gap - RF ground will handle the load. My 60
cycle cabinet ground is my backup. With tank circuit energies in
the megawatt range you can't afford to have a weak point.

Keep the physical distance between the base of the secondary coil
and the system RF ground as short as possible. I try never to go
further than 20 feet for low power stuff, and 15' or less for the
high powered work. Use the heaviest SMOOTH strap possible. I run 
two heavy straps; one from the base of the secondary directly to
system ground, the second snakes around and grounds everything
else. It is recommended that the grounding path be wired with
solid smooth straps, such as the strips of aluminum or copper 
used for gutter and downspout flashing. Woven braid ground strap 
has a much higher impedance in this application than does the 
solid smooth strap. You will find the smooth strap is also
more cost effective. This is a high Q Tesla grounding system. It 
gives the best coil performance, the most safety for the coil 
operator, and guess what?

People in my house, and the neighbors next door, can watch TV or
listen to the radio, with no snow or static! Even during high
power operation! I never get spark from my coil controls. All of
the RF currents that are not expended in spark are directly,
positively, grounded through a high Q ground path to a high Q
ground that is electrically isolated from all other equipment.

*********************************************************************
EDITED FROM DISCUSSIONS OF RF GROUNDING TESLA COILS. A LOT OF 
INFORMATION WAS TAKEN FROM A HAM RADIO DISCUSSION, BUT THE 
METHODS OUTLINED HERE DO APPLY TO BUILDING DEDICATED RF GROUNDS 
FOR TESLA TANK CIRCUITS AND RESONATORS. 
**********************************************************************

Quoting Richard Quick

I grounded to a hydraulic vehicle lift buried deep in moist clay. The 
lift was situated just feet from a foundation drain. My connection 
was made at the lift controls where my straps were clamped to both a 
hard copper air pressure pipe and a 3" galvinized hydraulic pipe, 
both of which went down through a concrete pad and connected to 
underground metal holding tanks. The tanks were also pressure plumbed
to the 14" diameter by 8' long piston housing. This hydraulic lift 
was powered from a remote air compressor. Since the air was fed to
the lift controls by a rubber hose, there were no electrical con-
nections of any type made to it. When it was used as an RF ground, it 
was electrically isolated from the 60 cycle wiring, and any other 
condutors as well. I am moving, so read it and weep with me. 

July 2, 1995

For the better part of an hour today I was scrounging for copper.
I came with about 35 pounds of assorted tubing, pipe, and strap.
I also came up with about fifty feet of aluminum flashing. Off
to the new lot!

July 3          Building my new Tesla Ground

I got out to the new home site yesterday afternoon. Supplies that
I brought along included a shovel, large hammer, some large steel
gutter nails, propane torch, solder, sheet metal screws and a
permanent marker. I picked up a couple of shanks of rebar that
were laying about.

With half of the foundation already backfilled in I focused on
the remaining trench. The soil is mostly rock, but the clay
filling in the gaps is a very rich red and very moist. I tried
digging, but a pickaxe would have been a better tool...

After about an hours work, I had only suceeded in trenching in
one 10 foot section of 14" inch aluminum flashing. Too much time,
too few results. I decided to unroll a heavy copper strap that I 
had dropped into the copper salvage box. This had been a strap
primary, unrolled it was fifteen feet long by three inches wide.
It was made up from three thicknesses of 10 mil copper sheet that
are spot soldered to prevent separation.

The deepest section of the foundation trench is about eight feet
below the ground and near the northwest corner. The corner was
carved out of decaying limestone by the heavy equipment, but the
stone is layered with the pasty clay, and the backfill dirt they
are using is trucked in. Using a length of rebar and the heavy
hammer, I chiseled out a vertical groove to fit my copper strap.
The top of the strap reaches the ground level about a foot from a
marked surveyors flag. I placed the strap in the groove, and
using the gutter nails I hammered it securely into place in the
rotting stone. Then I split the laminations of the strap open,
and where possible I drove a couple of rebar shanks into the
crumbling rock to further hold the strap into place. I wrote the
lot number on the top of the strap with the marker, and labeled
it as an "RF GROUND" and added "DO NOT REMOVE".

At the bottom of the foundation trench I unrolled about forty
feet of aluminum flashing. I folded it over once to get around
the foundation corner. Where it passed over the copper strap I
used a large nail as a punch, then screwed the two together with
sheet metal screws. I finished off by chopping up large lumps of
clay and burying the entire length of flashing.

Today it is raining and I am nursing sore muscles and a few
blisters on my palms. My clothes were all but runined... But
hey! I have got a pretty decent RF ground. If I recover before
the holiday is over I will head back out and pull up the end of
the copper strap and solder on some radials made from sections of
soft copper tubing. 

Richard Quick

**************************************************************************
Richard Quick to Steve Roys about RF grounds:

 > At the bottom of the foundation trench I unrolled about forty
 > feet of aluminum flashing.

 SR> We are having an in-ground pool installed Real Soon Now, and 
 SR> I had been thinking about the best way for me to use this to 
 SR> get a decent RF ground good for multi-kVA experimentation    
 SR> installed.  I thought about laying down aluminum flashing    
 SR> like you did, but I didn't think that the current-carrying   
 SR> aluminum would last vZ_ong buried in the ground?   

Copper is by far the preferred conductor of choice for RF
grounding. Aluminum works fine for awhile, then begins to
oxidize. This is in addition to the problems of electrolysis
when aluminum/copper connections are made without using a oxide
inhibitor. Still, my experience is that aluminum is cost
effective for the amateur coiler in RF ground applications where
the expected life span of the ground system is not much in excess
of five years, or where badly oxidized conductors can be easily
replaced. However, I do not rely on aluminum alone. My new ground
employs a significant amount of copper already, and I plan on
driving in some 8' copper pipes into the fill areas around the
property as soon as the grading is completed. But when it comes
to bang for the buck, any aluminum flashing you can throw down a 
hole or trench will help.
***************************************************************************