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