[Elecraft] Random Wire???

[Stuart Rohre]

A quarter wave of wire is not a hard thing to tune, it should be about the
impedance of the base of a ground mounted vertical antenna, depending on its
orientation, surrounding objects etc. An impedance from 30 to near 50 ohms.

Half wave wires are theoretical infinite impedances on their end, and are
the wire that is hard for some transmatches to tune.   Using ODD multiples
of a quarter wave will allow the end impedance that is matchable to 50 ohms
to repeat.  Ie, low end impedance is found for quarter wave, 3/4 wave wire,
1 1/4 wave wire, etc.

Even multiples are the half wave, full wave, etc.; each with thousands of
ohms of end impedance.

However, in all cases if a random wire does not tune with a given
transmatch, simply add more length to move the end impedance to a value that
is matchable.  Other techniques that work are to top couple to a LC network,
(high impedance end), whose coupling to station feeder is link coupled coax,
or a link tap up on the bottom of the L in the parallel network.  The half
wave wire is usually considered to be from 3000 to 5000 ohms end impedance
because of coupling to earth, end insulators, etc.

End coupled antennas require due attention to using a good RF ground as a
reference.  This may need to be quarter wave insulated wires from the
chassis of the transmitter strung out around the shack, or outside under the
"random wire" or run in another direction outdoors.  Multiple quarter wave
counterpoises or "radials" will allow the working on all bands for which you
provide an RF reference.  This will reduce the RF on the tuner chassis or
transceiver chassis that is always seen with end fed wire and inadequate RF
ground.

72, Stuart K5KVH