textfiles/science/teslacoil.txt

                                                                     
                                                                     
                                                                     
                                             
To: tesla-at-grendel.objinc-dot-com 
Subject: Tesla's RF Ground 
From: richard.quick-at-slug-dot-org (Richard Quick) 
Date: Thu, 6 Jul 1995 04:12:00 GMT 
>Received: from ns-1.csn-dot-net (root-at-ns-1.csn-dot-net [199.117.27.21]) by uucp-1.csn-dot-net (8.6.12/8.6.12) with SMTP id RAA07493 for <tesla-at-grendel.objinc-dot-com>; Fri, 7 Jul 1995 17:06:18 -0600 

--------------------------------------------------------------------------------

In re-reading the first fifty pages of The Colorado Springs Notes
(CSN), I have retraced again the construction and measurement of
the grounds that Tesla used there. In discussing this material
will quote Tesla's actual notes whenever possible.

On the first day that Tesla began coiling inside the building
at Colorado Springs (June 15, 1899), he had two metal to earth
connections available, the water pipe and the lightning arrestor
ground. Tesla notes: 

  "Sparks went over the lightning arrestors instead of going to
ground. This made it necessary to change the connection to the
ground, separating that of the secondary of the oscillator from
the ground of the arrestors. By connecting the secondary to a
water pipe, and leaving the ground of the arrestor as before, the
sparks ceased. This indicates a bad ground on the arrestors. THE
LATTER WORKED EXCEEDINGLY WELL. The ground connection was made by
driving in a gas pipe about 12 feet deep and gammoning coke
around it. This is the usual way as here practised."

First note that arcing was occuring from the earth connection
over the arrestors. This shows that the lightning arrestor
ground, an iron gas pipe driven twelve feet into the earth, was
insufficient for even a low power test. Tesla clearly recognizes
the differences between the two grounds he has available. The
capitalized sentence above was in italics in the original. His
setup is brand new. His tune is rough. 

The following day, June 16, 1899, he had workmen going full tilt
on a dedicated RF ground for his experiments.

  "A new ground connection was made by digging a hole 12 feet
deep and placing a plate of copper 20" x 20" on the bottom and
spreading coke over it again, as customary. Water was kept
constantly flowing upon the ground to moisten it and improve the
connection but in spite of this the connection was still bad and
to a remarkable degree. It is plain that the rocky formation and
dryness is responsible and I think that the many cases of damage
done by lightning here are partially to be attributed to poor
earth connections. By keeping the water constantly running the
resistance was finally reduced to 14 ohms between the earth plate
and the water main."

Tesla clearly notes the indivuality of the water pipe and the
earth plate, just as earlier he noted the difference between the 
arrestor ground and the water pipe. I will call the earth plate
the "dedicated RF system ground" or simply "system ground".
In text following the quote above, Tesla next refers to using a
"sensitive device" to determine the presence of a ground current
around the lab. I have used resonate pickup coils with a small
neon indicator bulb on the air terminal, or even a low pressure
gas tube to detect ground currents.

Apparently the water was turned off that night, for on the
following day, June 17, 1899:

 "Measurements of resistance between ground wire and water main
showed the surprising fact that it was 2960 ohms, and even after
half an hour watering it still was 2400 ohms, but then by
continued watering it began to fall rapidly. Evidently the soil
lets the water run through easily and being extremely dry as a
rule it is very difficult to make a good connection. This may
prove troublesome. The water will have to be kept flowing con-
tinuously. The high resistance explains the difficulty, from a
few days before, of getting the proper vibration of the second-
ary. The first good ground was evidently at the point where the
water main feeding the laboratory connected to the big main
underground and this was several hundreds of feet away. This
introduced additional length in the secondary wire which became
thus too long for the quarter of the wave as calculated. The
nearest connection to earth was as measured about 260 feet away
and even this one was doubtful."

OK, Tesla has said a mouthful. First his measure of resistance
when the water is off overnight skyrocketed. Though the water
expense was unbudgeted, it ran 24-7. (The bill was finally paid
when the wood used in construction was sold after the building
was dismanteled.). This shows that Tesla was determined that no
expense was to be spared in obtaining the lowest resistance
ground connection possible. 

Tesla then notes that the first true electrical ground point
occurs on the water main at the junction to the laboratory supply
pipe. He notes at the end of the quote that even this ground
point is doubtful, possibly because his equipment is powerful
enough to push the center of the "true electrical ground point"
further up the main. 

Tesla also notes that the ground path leading to the true
electrical ground point must be considered as a parasitic
conductor length in all secondary calculations. This distance
between the base of the secondary coil and the "true ground"
affected his ability to determine the resonate frequency of the
grounded coil and kept him from establishing a sharp tune in the
system. Add the fact that the location of the true electrical
ground point on the pipe may not be stable, and would possibly
move farther away with increasing power levels, meant that the
water pipe would be completely unsatisfactory for use as the
system RF ground.

To jump ahead to page 125, the section notes indicate that
stationary standing waves were observed on the water pipe, and
the exact electrical distance from the ground plate to the
electrical node on the pipe was determined to be 550 feet. This  
would be an unpleasant amount of uncoupled conductor to add to
any secondary coil.

In conclusion, Tesla recognized the need for a dedicated RF
ground in his coil systems. His specifications were such that the
true electrical ground point for the system ground had to lay as
close as possible to the base of the secondary coil. He
recognized the need for a highly conductive pathway adapted for 
low frequency high-voltage RF.

Reference:

> THE COLORADO SPRINGS NOTES, 1899-1900
By Nikola Tesla... Hardcover, 440pp, Published by NOLIT, Beograd,
Yugoslavia, 1978. Prefaced and annotated by Aleksandar Marincic,
Assoc. Prof. of EE Beograd Univ. and advisor to the Nikola Tesla
Museum, Yugoslavia

Richard Quick 

... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12


             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 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.
***************************************************************************
From Chip Atkinson
RE: RF Grounds

I was looking at a magazine and saw a little blurb in the handy tips 
from readers.  This blurb described how a guy puts in ground rods.  His
method works best in clay rich soils.  Here's what he does:

Dig a hole about a shovel wide and a shovel deep.  Fill this with water 
and push the ground rod in as far as you can.  This will be only about 
3" or so. Then pull the rod out of the hole and let the water fill it up.  
Then push the rod back into the hole.  From then on, don't pull the rod 
completely out of the hole, but just work it up and down, pushing it in 
a little farther each time.  He says that he can put in 8' ground rods 
by hand without pounding. I'll have to try that technique myself some-
time soon.

Chip
****************************************************************************
From K. Gakis:
 
The best grounding method I've heard of is to bury a 3'x3' piece of sheet 
metal about 3-4 feet into the ground, then drive a 8 ft stake down the 
center. One of my fellow hams used this at his station and I've never 
heard of any problems.

*****************************************************************************
From Mark Conway
RE: RF GROUNDS
 
Hi everyone,
 
Heres some more info on putting in ground rods etc that I got from
rec.radio.antennae*
  
Michael Marmor, mmarmor@pluto.njcc.com,
Subject:        Re: Best way to install ground rods?

>I recently bought an 8 foot copper ground rod to be used as my
>station ground.  Does anyone have any advice or tips on ways to
>install the rod?  I am concerned that it might bend if hit with a
>sledgehammer.  Also, does the 8 foot rod need to be driven all the
>way in to have an effective ground.  (I do not know how the soil
>conductivity is at the QTH here in Princeton, New Jersey; I imagine
>conductivity dictates how deep the rod must be to function
>effectively)
> 
>73
>Michael, AA2UJ
>mmarmor@pluto.njcc.com
 
I received many replies to my post about installing ground rods.  
Since this info may be of use to other amateurs installing antenna
systems I will post some of the replies I received.
 
Michael
______________________________________
 
From gsparks@ix.netcom.com  Thu Jan 12 10:25:28 1995
 
I don't know your soil.  I work in a clay Gumbo soil in Houton, Tx.
 
The way I install ground rods, I have 6 in a 1x3 meter square, is to 
take a water hose and soften the soil a bit, then just start pushing the 
rod a little, then lift it out of the hole, fill with water and repeat. 
Don't go over 4 or 5 inches at a time making sure the water lubricates 
the hole and rod.  This takes about 30 minutes, don't use to much water, 
you don't want to wash the hole out.
 
If this doesn't work build a driver for the rod, to do this take a peice 
of steel or iron pipe about 4' long, put a cap on one end, slip over the 
ground rod and use this to drive the rod, when you get to the 4' level 
you can use a shorter piece of heavier pipe, or a real good friend and a 
large hammer.  I dig a hole and bury my rods complete, along with the 
ground wire just for mowing and tripping reasons, in fact if I can't get 
the rod clear in, I cut if off with a torch.  I also Braise, not solder 
the ground wire and use #4 fine strand wire.
 
Sparky  KI5GY
 
-----------------
From: tigger@prairienet.org (Sean E. Kutzko)
 
Hi, Michael-
 
I was skeptical with this ground rod installation tip, until I tried it 
out. It REALLY does work:
 
Dig a little hole (say 6") where you want the rod to go in place. Get a 
large bucket of water and fill the freshly-dug hole with it. Jam the rod 
into the water-filled hole. Lift out and jam back in. Repeat as needed.
 
The secret here is to make sure the hole for the ground rod is kept VERY 
wet. This way, the water is doing all the work for you. I slapped an 
8-footer into the ground in 5 minutes this way; no sledge hammer needed.
 
Depending on the type of soil you have, you might need a sledge for the 
last foot or so. Once you hit it with a sledge, the back-and-forth 
jamming process won't work any more, so be sure you REALLY want to use a 
sledge on it.
 
BTW, get that sucker as far into the ground as you can. If it's an 
8-footer, then sink it 7 and a half feet.
 
Good luck,
 
Sean
_____________________
 
From: HarrisR@yvax.byu.edu (Richard Harris)
 
I drove my 8' ground rod using a fence post driver.  The post driver 
that I used is one that is made to drive T type metal fence posts.  
This allowed me to drive the post in about 6 feet or so and then I used 
a sledge to finish driving the rod.  I would drive it in all the way 
and make sure that it is at least 6 inches below grade.  I hope yours 
goes in better than mine.  I have very rocky soil and it took me 2-3 
hours.  I have put rods in soil without rocks in 10 minutes.
 
good luck and 73
 
Richard Harris
KJ7CU
____________________
 
From spikes@hpscit.sc.hp.com  Thu Jan 12 13:10:17 1995
 
You put it in with a ~2 foot piece of pipe with an end cap and a handle 
or two on it. You can rent 'em from rental places or sometimes the local
home Honey-Do Emporium. Wear the thickest, foamiest gloves you have so 
you'll be able to feel your hand when done pounding. How far in depends 
on your year-around soil moisture conditions....yup, all the way in, 
unless you hit an aquafer!  :)  Leave about 6" out for connecting your 
wire and then spray paint it to keep the oxidation down. On the same day, 
once a year,when you change the batteries in your smoke detectors, go out 
and check/tighten it.
 
I put a BLUNT point on mine to help go arount the rocks and hardpan. A 
sharp point makes it wander too much.
 
The latest one was for 240VAC hot tub gounding. It has GOTTA work!
 
Bill
wb6rzg
_________________________
 
From hamilton@BIX.com  Thu Jan 12 13:43:10 1995
 
You should be able to drive the ground rod directly with a sledge
hammer unless when you say it's a copper rod, you mean REALLY
copper (pretty unlikely), not copper-clad steel.  It's best if
you pick a day when the ground is somewhat wet as that'll make
it easier.
 
The only really tough part comes if you hit a big rock.  You may
be able to break right thru it if you keep banging with the sledge
but depending on what you've hit, you may be forced to pull the
rod back out and try somewhere else.  If you're already down 4
or 5 feet, pulling it out can take some real work!  You may have
to dig it out!
 
In answer to your other question, yes, you do want to get it down
all the way into the ground, but part of that's just because having
it stick up out of the ground looks terrible. :-)
 
I just moved so I've been redoing my grounding also.  In my case,
I went with the solid brass rods from I.C.E.  These are available
only in 6' lengths (they're cut from 12' stock), so to make up for
that, I got 4 of them, which I arranged as one in the center and
the others every 120 degrees at a roughly 2' radius then joined
with 1/2" copper tubing to the center, where other connections
are made.  (Actually, btw, I am curious if others have comments on
the I.C.E. ground rods.  I was attracted by the non-corroding aspect
of a solid brass rod but disappointed not to be able to buy it in
an 8' length.   OTOH, if it's sold by I.C.E., I was hopeful they
should know what they're doing.)
 
Also, in my case, I wanted to but my rods under some decking right
behind the house since that'd be both closest to the shack and
out-of-sight and not a hazard someone might trip on.  But since
the deck only allows about 5' of headroom under it, I first just
used a shovel to dig down about 3' before driving the rods with
a sledge; once they were in far enough, I could push the soil
back in place.  Digging out that first few feet had the side
benefit of giving me some idea of how much rock I was likely to hit.
 
Regards,
Doug Hamilton  KD1UJ  hamilton@bix.com  Ph 508-440-8307  FAX 508-440-8308
_________________________
 
From rossi@VFL.Paramax.COM  Thu Jan 12 15:02:27 1995
 
Is this by chance a Radio Shack 8 ft ground rod?
 
I bought 2 of them.  Not bad, but a few weeks later I found virtually 
the same thing at the new Home Depot for less than 1/2 the price :-)
 
Anyway...  I drove 2 of them in but in both cases, they had a 2-3 foot 
head start (started from the bottom of a hole).  I got up on my 8 ft 
step ladder at the beginning and used an 8 lb sledge hammer.
 
It is kind of hard to get them started since after each wack they tend 
to >>> boing / wobble <<< around after they are hit.  Makes aiming the 
next wack a bit difficult.  I did it all by myself.  I certainly would 
be easier with a helper to hold the rod (then I can hit his hands when 
I miss :-) )
 
One thing I have read, and I did once before (I expect to try this 
for the 4 more that I have to drive in) is to get a short section of 
threaded steel pipe with an ID just large enough to fit over the ground 
rod, and put an end cap on the steel pipe then slide it over top of the 
ground rod. It will give you a slightly larger target to hit.
 
Once you get the rod started you just have to keep at it.  Take your 
time. Try not to miss.  You will feel it go in with each wack but you 
will also feel it when it hits a rock (very rocky soil around here).  
But I kept wacking away and it would start to go down again..  I got 
both of them in the full 8 feet.  My goal is to have 4 8 footers at the 
base of my tower and at least 2 more 8 footers where the cables enter 
the house. 
 
I would do what you can to go the full 8 feet if you really want them 
to do the job.  If you really can't go 8 feet then (and you know this 
in advance) the next best thing would be to go with twice as many 4 
footers (or 6 foot). If necessary buy/borrow/rent/steal:-) a bigger 
sledge hammer.  I would say 8 pound is minimum.  A 12 or 16 pounder 
should drive a rod through almost anything short of thick concrete :)
 
One more thing.  The radio shack ground rods had a reasonably nice point
on the ends.  The ones at Home Depot did not.  You should try to grind a
point on them if you can ESPECIALLY IF YOU HAVE ROCKY SOIL.
 
It goes without saying.  Don't drive in any ground rods if there is
any chance of hitting anything below.  Saftey glasses are not a bad
idea too :-)
 
Pete Rossi - WA3NNA
---------------------------

 > I have considered jetting down a ground rod but I don't think 
 > the contact with the ground would be as good as a driven rod.

I have heard exactly this.  In fact, the ARRL made mention of it in a 
past issue, that in many types of soils, most of what is left after 
using water pressure to make the hole, is stones.  All of the con-
ductive earth is washed away, and the worse conductors are left in 
contact with the ground pipe.  Measured ground conductivity is worse 
after using the water method.  The other thing is that pipe tends to 
clog, then freeze, and split open.  I much prefer the 5/8" galvanized 
ground rods that are commercially sold.  Yes, you have to beat on them 
for 10 minutes to getone in, but unlike pipe, they don't buckle under 
the beating, and they last.
 
Bruce N9EHA
 
Remember that a lightning bolt has a surge current of around
8,000 amperes. You have to size and bond your conductors to
handle this load. The duration of the pulse is short, however,
only about 20 coulombs of charge is exchanged in the typical
strike, so the conductors don't have to be large enough to
handle the surge *continously*. Copper conductors equivalent
to #6 solid wire are sufficient. 
 
Lightning is RF, though most of its energy falls below 2 MHz, 
so the skin effect must be considered. That's why solid strap 
is preferred over round wire. Strap has a larger surface area, 
pound for pound, than round copper wires. Copper pipe can also
be used, but it's surface area will be half that of copper
strap with a width equal to the pipe circumfrence. That's 
because the *inner* surface of the pipe forms a waveguide 
beyond cutoff for the lightning RF currents, and isn't effective
at carrying away the surge. Strap, on the other hand, can fully
exploit *both* surfaces. (Pipe *does* have somewhat lower inductance,
so there is a tradeoff here.)
 
Woven braid conductors should be avoided for grounding runs because
braid has about 5 times the impedance of smooth solid strap on a
pound for pound of copper basis. There are a couple of reasons
for this. First, the braid strands weave in and out, adding inductance,
and second, because the skin effect tries to force currents to the
surface, while the individual strands keep diving into the middle
of the bundle, the currents try to flow from strand to strand along
the outside of the braid. Since the mechanical connections of one
strand to another are fairly loose, a high resistance path is formed.
Fully *tinned* braid is better, since the strands are now bonded 
to each other better. However, solder *will* melt during a strike,
and you should plan to depend only on mechanically bonded connections,
IE clamps or cadwelding.
 
Since you are building your house, you have an opportunity now to
install a *Ufer ground*. Mr. Ufer developed this technique during
WWII for army ammo bunkers. The NEC approves its use for commercial
and home grounding systems. In essence, a Ufer ground is just rebar
in concrete. When the builder is preparing to pour your slab, make
sure all the rebar in the slab is bonded together, either cadwelded
or mechanically clamped, before the pour. And make sure to leave a
convienent attachment point exposed. A rule of thumb for a Ufer
ground is that it takes about 20 feet of 0.5 inch rebar to absorb
8,000 amperes of surge. More is better. The rebar should be embedded
in at least 4 inches of concrete.
 
The way a Ufer ground works is through two paths. First it forms
a large capacitance to Earth. This is an excellent RF coupling.
Second, concrete's ions generally are more conductive than native
soils, so you have a large number of virtual resistors in parallel
connected to Earth that offer a lower resistance than would a
smaller collection of driven rods. Earth is actually a lousy 
conductor. Most currents are dissipated through Earth by capacitive
coupling and arcing from soil grain to soil grain. Concrete is a 
better conductor since the grains are tightly bound together.
 
Gary
************************************************************************** 
Quoting Richard Quick to Mark Conway:

This was some excellent information. Thanks Mark for posting this
up. More than a few people here are either building coil systems,
or upgrading to higher power levels. I have always said that
Tesla coils literally have to be hand built from the ground up.
 
 MC> Over on the radio amateur echo somebody was saying that this 
 MC> method <soaking the soil> is not the best for putting in     
 MC> ground rods as the soil does not make good contact with the  
 MC> rod as the water washes the soil away from the rod.
 
Just a heavy soaking is not going to hurt. The practice that I
think was specifically being advised against was pressurizing
a pipe with water and then using the water flow to assist in
getting the pipe into the soil.
 
Bruce N9EHA said:
 
 > the ARRL made mention..., that in many types of soils, most of 
 > what is left after using water pressure to make the hole, is   
 > stones.  All of the conductive earth is washed away. 
 
But, a good soaking brings particulate dirt and clay in close
contact to the conductor. 
 
Then quoting Gary Coffman KE4ZV
 
 > Lightning is RF, though most of its energy falls below 2 MHz, 
 > so the skin effect must be considered. That's why solid strap 
 > is preferred over round wire. Strap has a larger surface area, 
 > pound for pound, than round copper wires. Copper pipe can also
 > be used, but it's surface area will be half that of copper
 > strap with a width equal to the pipe circumfrence. 
 
This is why I used 15 foot long by 3 inch wide copper strap for
the center of my new ground. Again quoting Gary Coffman:
 
 > Woven braid conductors should be avoided for grounding runs    
 > because braid has about 5 times the impedance of smooth solid  
 > strap on a pound for pound of copper basis. There are a couple 
 > of reasons for this. First, the braid strands weave in and     
 > out, adding inductance, and second, because the skin effect    
 > tries to force currents to the surface, while the individual   
 > strands keep diving into the middle of the bundle, the         
 > currents try to flow from strand to strand along the outside   
 > of the braid. Since the mechanical connections of one strand   
 > to another are fairly loose, a high resistance path is formed.
 
This is a pretty good argument for using wide smooth strap in the
ground path. I have known for some time that strap performs
significantly better than round wire, and have said that the
widest possible strap is better than the skinny stuff (this is
easily experimentally verified). 
 
One other thing that I thought someone might mention, but
considering the different applications that grounding is used for
perhaps not; the use of salt in RF grounding applications. Rock
salt or water softener salt can be buried around the ground
conductor. A depression in the surface of the ground is left and
the area is given a good soaking before firing. A section of PVC
pipe could be partially buried around the ground conductor,
filled with salt, and then soaked before firing. The other way is
to perforate the end of a grounding pipe before planting it and
then rig up a simple gravity pump with a saturated saline
solution.
 
Salt plumes are fairly inexpensive and easy to build up in the
subsoil. They are non-toxic, with the exception perhaps of a tree
root passing directly through it. The presence of an established 
salt plume will really increase the local conductivity. Watering
the ground before firing makes an excellent connection between
the ground conductor and the salt plume. 
 
Richard Quick
**************************************************************************

Richard Quick on the salt pipe RF ground.

This is one of the easiest, cheapest, and most effective RF grounding
techniques for Tesla coilers. This ground is not cost effective for use 
24-7, but when used occasionally (daily for a few hours) for RF ground-
ing tank circuits and secondary coils you will get a lot of "bang for 
the buck". This ground also improves over time.

It is best to select a low spot or natural drainage area that is as 
close as possible to the base of the Tesla coil. Try to get the inital
placement within 15 - 20 feet of the Tesla lab. You will need the 
following materials:
----------------------------------------------------------------------------
TWO, 8 FOOT COPPER CLAD STEEL GROUND RODS, (good)
OR
TWO, 8 FOOT LONG BY 3/4 INCH DIAM. HARD COPPER WATER PIPES (better) 
or
ONE, 8 FOOT LONG BY TWO INCH DIAMETER GALVINIZED STEEL PIPE (best)
-----------------------------------------------------------------------
TWO HUNDRED POUNDS OF ROCK SALT OR WATER SOFTENER SALT
-----------------------------------------------------------------------
ONE HUNDRED POUNDS OF COARSE SAND AND A FEW BUCKETS OF GRAVEL
-----------------------------------------------------------------------
A FOUR FOOT LENGTH OF VERY LARGE DIAMETER PIPE (10 INCHES DIAM. MIN)
-----------------------------------------------------------------------
ONE ROLL OF FOUR INCH or SIX INCH WIDE ALUMINUM STRAP (gutter flashing)
-----------------------------------------------------------------------
ELECTRICAL OXIDE INHIBITOR
-----------------------------------------------------------------------
HOSE OR OTHER CLAMPS FOR THE ROD OR TUBE CONDUCTORS 
-----------------------------------------------------------------------
DIGGING AND TRENCHING TOOLS
----------------------------------------------------------------------------

Start by digging a hole at least four feet deep that will accept the 
large diameter pipe. It is advisable that a two foot or three foot 
diameter pipe be used. PVC, corrugated culvert, concrete, iron, 
really any type of pipe may be used depending on what is available.

Once the hole is dug, case or line the hole with the pipe, then fill 
with water. Do not allow too much of the casing pipe to remain above
ground level, a few inches is OK. Next, work (or drive) the rod (or 
tube) conductor(s) into the earth at the bottom of the cased and water 
filled hole. It is important that as much conductive rod or tube as 
possible be in contact with the earth. Place the vertical conductors
near the edge of the cased hole. If two vertical conductors are used 
then place them on opposite sides of the hole.

Once the vertical conductors are in place, trench a path back to the 
Tesla work area. Make the trench wide enough to accept the four inch
or six inch smooth alumium strap (gutter flashing). Make sure the 
trench is below the sod level. 

Smear the top(s) of the vertical conductors with a light coat of
electrical oxide inhibitor. This compound is used to prevent 
corrosion whenever electrical connections between disimilar metals 
are made. Once smeared with inhibitor, wrap one end of the aluminum 
strap around the vertical conductor and clamp into place with a hose
(or other) clamp. Verify the connection with a VOM. If two verticals 
are used then use two separate lengths of aluminum strap. Place the 
strap into the prepared trench back to the Tesla work area and back-
fill the area in.

Next pour a few inches of gravel into the bottom of the cased ground
hole. Begin to backfill the cased hole by alternating shovels of salt
with half shovels of sand and gravel. Continue until the hole is filled.

The ground is left dry when not in use. Before firing coils, fill the 
ground hole with water. The water will dissolve the salt which then 
migrates downward to form a conductive "plume" in the subsoil. The salt 
will require periodic replenishment. Over time, and with continued use,
the salt plume will make contact with bedrock or the water table. 

The vertical conductors will corrode fairly quickly in the presence of
the moist salt. After a few years new vertical conductors should be 
driven in and connected alongside the old ones. The alumium strap that
is used to make the run between the lab and the ground pipe will also
corrode and will need to be renewed after a few years.

Improvements to this ground may be made by substituting copper strap
for aluminum strap in the construction. Copper will last longer and 
will make a better connection to the verticals. As mentioned above
the best connection is braised. Another improvement can be made by 
clamping a conductive mesh screening to the vertical conductor in 
the cased ground hole. This will allow a greater surface area of 
contact with the salt water. The best mesh is either copper, steel
or stainless steel harware cloth. Do not use aluminum screening.

The purpose of the sand and gravel is to prevent caking of the salt
which will prevent water from passing through the ground hole. When 
the salt is replenished it is a good idea to remove some of the sand
amd gravel or otherwise mix the sand and salt together. Dumping in
a large quantity of salt all at once without some inert filler will
cause a salt block to form that is difficult to break up or dissolve.

The theory of operation is pretty simple. The casing pipe prevents 
the salt from migrating sideways in the surface soil where grass, 
bushes, and tree roots would be poisoned. The salt dissolves and
travels downwards into the moist subsoil, while at the same time
spreading out laterally. When the "plume" contacts the water table
a connection is made. If the soil is very dry and shallow the plume 
will desend to the bedrock and will then expand laterally which forms
an underground plane. In either case the ground that is formed is
high quality, and is ideal for even very high powered Tesla coiling 
without modifications.

Richard Quick

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