Ground-Plane - RF Construction & Testing
Date: July 12, 04. One can not really compare resonance transformer grounds with commercial power. The freq difference between 60 Hz and 500 KHz demands a much better ground system on the secondary inductor. Conductivities at 60 Hz are inconsequential to good RF design. HF RF requires the best ground that one can provide. Use the hole, throw in a tablespoon of salt, add some water, and the re-drive the ground. The migrating sodium ions will help provide a much more effective ground plane and a bit of water also helps. Better grounds usually equal slightly longer sparks. We always use a pair of copper rods with salt and water. The copper rods are driven approx 20 feet apart and connected with 2 ought welding cable. Dr. Resonance.
Date: Sat, 10 Jul 2004, 22:17:25 -0600, Subject : Re: An Electrolytic ground plane: Just like in high voltage transmission lines, the voltage is very high but the current is low. Thus, a bunch of resistance in your ground plane is not going to matter much. Wet dirt is far overkill!!! Search the web of the term "counterpoise tesla". Radial wires give a very good ground plane while avoiding circular eddy currents that may steal power from the primary coil. Cheers, Terry.
July 11, 04: The above is is what I did today, two 7' lengths of 1/4" k type cu tubing with about 5 inches soldered to the cleaned 8' ground rod, and a 3" wide cu strap soldered around the top for a better contact. I critically measured the connections from both secondary coils to the ground rod and will repeat the measurements shortly. John C.
Date: Sun, 6 Dec 1998, Tesla List wrote: A counterpoise usually consists of a radial network of wires starting from the base of a vertical antenna, and extending out to a radius of at least the antenna height. The purpose is to reduce the losses due to current flowing in the ground. Where the ground resistance is high enough it is common practice to mount these wires on short poles above the ground. In the case of a Tesla coil the ground does two things. It certainly provides a return for the current which flows through the coil, and for that purpose a wire screen of radius equal to the height of the coil should do a commendable job. (I guess really it would be better to extend it beyond the range of the longest streamers.) The second purpose of the ground is safety - to keep any part of the coil from having high power line voltage on it if for any reason the power transformer inadvertently becomes connected where it shouldn't. A counterpoise won't take care of that at all, so some sort of fairly low resistance ground is needed to make sure the operator and his friends stay alive in case something fails. Ed.
Resent-Date: Sun, 6 Oct 2002 22:08:04 -0600: Why bother? Just get a six foot grounding rod from your local Home Depot, pound it into the ground, and attach a thick braided wire from it to your RF ground on the Tesla's secondary. No need for fancy or heavy grounds. Sure, a lot of people on this group think you need some serious ground with serious ribbon type grounding cable, but I operate my coils (currently up to 5kVA) with a simple set-up shown above. Also, one coiler I know runs his coils (up to 20kVA) using only a 12 AWG solid ground cable to a similar rod and that guy is getting some serious output - no problems there.
July 14, 2004. Tesla List. Hello all, It is my experience that one copper tube in salt seawater is no good as a HF ground. I had to use several pieces of galvanized or chicken-wire, connected together, as a counterpoise in harbour along the North Sea coast. I was using the au mast of my sailboat as an antenna on a frequency of several MHz. As a tip on the use of HF earth electrodes: Drive several copper tubes in the ground with the help of water pressure. Flatten the end and turn the tube a little with some pumping during the action. Then fill the tube with one pound of copper-sulfate and pump this with the water pressure into the ground. This will make the ground better conducting and also keep the tube from being corroded. Salt is not so good as it will be leaching away and help corrode the electrode. The copper sulfate will stay in place in the ground for a long time. As an alternative, make a small deep hole along each driven electrode , put a handful of copper-sulfate crystals in each hole and water these regularly. This tip comes from an old ARRL book. Regards, Willem, PA0TW
July 11, 2004.
Original poster: Jim L. What you describe makes a fine DC ground,
and might provide a suitable
connection for grounding lightning impulses, but doesn't do much for RF.
The RF ground properties are going to be more determined by the type of soil you
have, and most particularly, the water content. All an electrolytic ground
will do is dissolve your ground rod more quickly. For RF grounding, what
you want is a GOOD conductor that is CLOSE to the coil (i.e. a short wire from
bottom of secondary to ground), as in directly underneath it. Sheets of
aluminum or copper would work quite nicely. Chicken wire/aviary netting
would be a close second. Unless you are making sparks 50 feet long, the
earth properties aren't going to be all that important.
Of course, if you dispense with the ground plane, and run a wire to a ground
stake, then what you are really depending on is the RF conductivity from that
rod to the floor under your coil. If you run your coil over a concrete floor,
then you're actually in pretty good shape, because concrete is a fairly good
conductor.
It's important to remember that Tesla Coils are neither electric power grids nor
HF antennas, and most of the literature you will see on grounding pertains to
those two applications. Even if you look at MF and LF antenna grounding
systems, they're not really relevant, since in the antenna case, what you're
interested in doing is propagating a wave away from the antenna. However,
in the sense that the typical broadcast worker wants to minimize IR losses in
the antenna system, as you do with a Tesla Coil, then the advice is sound. The
classic George Brown 120 radials scheme would work fine. Note that in his
work, and in much subsequent analysis (Rudy Severns did some nice work in
connection with vertical antennae for hams) some general expressions for the
current density induced in the earth are derived, allowing you to optimize the
length and number of the radials. In general, extending the radials a bit more
than the height of the antenna is warranted.
Taking this for the TC world, it would turn into the usual recommendation that
the conductive counterpoise/ground plane should extend out as far from the TC as
the top of the TC is above the counterpoise. If you have a 4 foot high TC
sitting on a 2 foot high table, your counterpoise should be on the order of 12
feet in diameter.
For safety, you should connect your RF ground to the "green wire" ground, but
that can be a high RF impedance. It's to keep you from getting zapped by 50/60
Hz line current. In fact, a choke might not be a bad idea, to keep RF out of
the green wire ground.
July 12, 04. RF Ground plane