[Elecraft] Counterpoises and Grounding

[Jim Brown]

On Sat,6/10/2017 11:40 AM, Stan GW3SRM wrote:
> I note that the subject of counterpoises has been debated many times in this
> forum but I have not seen the subject of tuneable artificial grounds
> discussed.

Fundamental concepts like this are very well addressed in the classic 
references on antennas. Your use of the word "counterpoise" is precisely 
correct. Your use of the word "ground" is absolutely and totally WRONG.

A connection to Mother Earth does NOT make a transmitting antenna work 
better. The earth is a big resistor. Shoving TX RF into it wastes TX 
power by warming worms.

What IS needed, no matter where you operate, is a return for antenna 
current -- SOMETHING to act as the other half of the antenna. Antennas 
like a dipole inherently provide that; with an end fed antenna, we must 
supply that "other half," and the correct name for it is "counterpoise."

Transmitters are designed to work into some defined load Z, usually 50 
ohms, but with some tolerance. That tolerance is often defined by the 
apparent SWR as measured at the transmitter. The function of an antenna 
tuner is to transform the Z at the transmitter end of the feedline to 
the Z that the transmitter want to see -- that is, the Z into which it 
will provide the most power, and do so without stressing the output 
transistors or tubes. The so-called "artificial grounds" provide the 
same function, but in a different way -- they vary the electrical length 
of the counterpoise so that the combination of the "intentional antenna" 
(the end fed wire) and the counterpoise make the Z at the transmitter as 
close as possible to 50 ohms. This allows the TX to put power into the 
antenna. That counterpoise, whatever it is, is PART OF THE ANTENNA. And 
that's true whether we CALL it "ground" or counterpoise.

Another point. ALL end-fed antennas must put their return current 
SOMEWHERE. If we don't provide a "good" path  (like a good 
counterpoise), mother nature will take over and put the current where 
SHE wants it to go, like anything attached to the chassis of the 
transmitter. This can be a coax shield, the power system protective 
earth (green wire), a wire going to a ground rod, even telephone wiring 
or CATV wiring connected to that ground rod. (Remember, the earth is a 
big resistor). KK9H, a fairly smart engineer who is one of my old 
buddies in Chicago, intentionally uses the HVAC air ducts in his home as 
a counterpoise for a 160M wire. At my last Chicago QTH, I used a big 
wrought-iron fence running around the front of my lot as a counterpoise 
on 160 and 80 for a Tee-vertical.

A connection to mother earth is important for only two reasons. First, 
and most important, for lightning protection and electrical safety. 
Second, for SOME receiving antennas, where the resistance of the ground 
makes the antenna work, or where the loss of efficiency caused by adding 
the resistance to an RX antenna doesn't matter.

SO -- let's stop using (or thinking about) the word "ground" in 
conjunction with TX antennas, and in stead, talk (and think) of 
counterpoise.

73, Jim K9YC