On Jul 14, 11:05 pm, Bill B wrote:
I made a 15 inch square (broadcast band) loop antenna using 2 crossed
pieces of wood and about 14 turns of number 18 copper wire. I added
spreaders in the center sections to increase the spacing between the
windings and reduce the distributed capacitance. Works well and has a
Q factor of 100 or more at 600 KHz. I get about 800mV from a local
50KW station.

But the wire is concentrated around the outside perimeter of the loop
and I'm wondering if there is an advantage in winding the loop so that
the wire occupies more of the interior space. This would require a
longer winding to maintain the same inductance and would further
reduce the distributed capacitance, but would also increase the total
resistance somewhat. Seems like a longer winding in the same space
would produce a larger voltage, but at the expense of some additional
resistance which may degenerate it somewhat.

What would be the optimum given a 15X15 inch square space?

-Bill

Optimum is wire around the outside. You want to capture as much of
the field as you reasonably can. Imagine it this way: if you have a
15x15 loop and put say a 5x5 loop inside it, co-axial with it, and put
the two in series, you get the sum of the two. But what is the
performance of a 5x5 loop relative to that of a 15x15 loop (given that
both are much smaller than a wavelength)? There's still some question
about the optimum arrangement of the wire around the outside, though.
The largest area (the largest total field flux) enclosed by a fixed
length perimeter would be where the perimeter is a circle, so there's
some advantage of making the loop more circular. It's not terribly
likely you'll notice much difference from your square, though. But
you might find it useful to download one of Reg Edwards' legacies,
RJELOOP3.EXE, "Multi-turn, square, frame (or loop), receiving
aerials." It will let you play with different wire sizes, numbers of
turns and wire spacings, and give you a good approximation of the
expected Q, equivalent shunt capacitance and efficiency.

Small loops at low frequencies can be useful at rejecting locally
generated noise from things like electric motors or even
microprocessors, because that near-field noise tends to be
predominantly electric field which is vertically polarized, but to do
that well, the loop must be symmetrical about a vertical axis.

Cheers,
Tom