[Elecraft] K2 fixed, but now what?

[Ron D'Eau Claire]

Excellent comments George. I'm sure that you remember when a "dipole"
meant that it was a HALF WAVE radiator. Whether or not it was fed at the
center, at one end or somewhere in between did not matter. Accordingly,
an antenna was not a half wave long is NOT a dipole, even if it's fed in
the center or sold with "Dipole" written all over the packaging. 

Well, that's still true in Engineering circles, but out here in "hamdom"
the meanings get changed radically. It's with some trepidation that I
start allowing "ham" definitions into my vocabulary because it makes
life so darn confusing when talking with engineers. 

You make an excellent point about "counterpoises",  It's one that I've
gotten careless with. 

Following up on your statement, it might be useful for ops just
discovering them that one of the best ways to "adjust" such a "floating
ground wire" for the best length is to adjust it for maximum current
flowing into it at the rig end. The idea is to have the lowest possible
r-f impedance at the rig end. Lowest impedance = largest r-f current for
any given power level and minimum r-f voltage at the rig end. That's the
idea. Keep the rig cabinet at r-f "ground" or as close to it as
possible. 

You can adjust the length of the...er....ahhh.."counterpoise"  wire for
maximum current or use a simple little "matching" network. MFJ makes a
so-called "artificial" ground which employs a simple L/C network to
adjust a "counterpoise" wire for maximum current. I have one such
"artificial ground" built into an MFJ 934 ATU that works very well.
Another approach is to use a slightly short wire and a small coil to
bring it up to "resonance". 

The MFJ comes with a rudimentary but effective r-f current meter for
adjusting it for peak current.  With a homebrew circuit, maximum current
is easily measured with a 50-cent r-f ammeter - what most of use
recognize as a flashlight bulb. At QRP levels such a device works very
well to indicate r-f  current when placed in series with the wire.
Remove it from the circuit when you have 'tuned' for maximum brightness.
Buy two, at least. It's amazing how easy it is to burn them out <G>.

73,

Ron AC7AC
K2 # 1289

-----Original Message-----

The term "counterpoise" has come to mean many things in amateur radio
usage and I will steer clear of trying to give any sort of generally
accepted technical definition for the term. The function of a true
counterpoise differs from that of the wire under discussion, but it
matters little what we decide to call it - the wire works the same
regardless.

Historically, the term "counterpoise" originally was used to describe a
system of wires placed near but not on the ground to provide an r-f
connection to ground by means of the capacitance between the
counterpoise and the actual ground.... 

The purpose of the wire that Tom is recommending is not primarily to
provide a capacitive connection to the Earth (which it does to a degree)
but rather is to place the cabinet, chassis, etc. of the K2 -
specifically the GND post on the rear panel - at as near zero r-f
potential as possible. ...

If the wire is 1/4-wavelength long at the operating frequency, has its
far end insulated and is not too close to the ground or metallic
structures - either of which would serve to detune it - then in the
near-field of the radiating portion of the antenna system, the wire has
current induced in it. This current sets up a voltage gradient along the
wire, with the "far end" having a voltage maximum and the end connected
to the radio a near zero voltage level, due to its 1/4-wavelength
dimension.
...
<steps down from pulpit>

73/72, George