[Elecraft] OT: SGC Coupler / Small Wire Loops

[Stuart Rohre]

The low series impedance in the conductor circumferential length is to allow
the current to circulate at low loss, but the impedance at the gap across
the open spot in the loop goes toward infinity, (open circuit, right?)

A cap bridging that spot then will see a high potential difference at the
spot opposite the feedpoint location.  Some loops are fed by a tap
moved around the loop feedpoint side, as in a gamma match.  One
experimenter has another scheme, which is an insulated conductor
wrapped around part of the loop.  I have never  seen a picture of it,
and the description made it sound like it originates on one side at the gap
in
the loop where the cap for tuning goes, and winds for a portion of the
circumference.

Our laboratory has been experimenting will various small HF Antennas for
over a couple of years.  Many copper pipe loops have been built to
compare them to our staff member, Bob Rogers's invention of the FLEX
Folded Helical Conical vertical.  This antenna has much less height
than typical single turn HF loops, at greater efficiency when measured
in the Wheeler Cap, a large can used to enclose an antenna for
efficiency computation by comparing open field S parameters to
enclosed field S parameters.  Some of the Loops are small enough
to be measured in the largest Wheeler Cap we built.  (We have two).

Perhaps the best description of the advantage of the large conductor
element loop, is that it is capable of passing high currents in that
region of the loop where the current peaks, and also the large
conductor lessens the chance of corona discharge at the gap in
the loop.  Breakover in the capacitor and losses at that gap can
nullify the size of advantage of the loop, by limiting the power that can
be transmitted.

73, Stuart K5KVH