Regarding the single turn versus multiple turn loop, I have done both.
For the multiple turn loop, 100 meter of 1.2 mm PCV clad electrical mains
wire was wound on a wooden frame with sides of 70 cm. This was a major
task in itself and called for a dedicated winding contraption.
The primary could be tuned from 120 - 600 kHz and the secondary was a
single turn winding. Output was fairly low and a broadband pre-amplifier
The single turn loop had a diameter of 1 meter and was made from the outer
shield of a length of RG213 coaxial cable. The stepup transformer was
wound on a 36 mm high mu (5000) toroid. The primary had 3 windings and the
secondary 90. Still a lot of turns, but more manageable tahn winding the
multiturn boxed loop. The output was fed into a high input buffer
amplifier (aka mini-whip). Though small, this loop provided ample output
and the output was shunted by a 33K resistor to give the same output at Lf
as my mini-whip. This is a broadband antenna and besides being plagued by
local noise, reception is excellent.
The multiturn tuned loop has the benefit of being very selective and is
nice to prevent IMD. The broadband loop is easier to use of course and
with the right gain setting will not cause IMD on most receivers.
The beauty of this hobby that most of the time we have a choice!
Roelof bakker, pa0rdt