Untuned loops like to be large single turn things.
I taped two 4 ft long fiberglass driveway marker rods
for a 7 foot span last night and draped wire off the ends.
A 2 turn, 3inch diameter coil was wound onto one side,
to couple to the pocket radio.
The reception boost was fantastic.
3-4 turns on a 24inch square were not even close.
It's awkward to find supports and clearance, but ~18 ft
of wire straight across a 7 ft top boom, hanging down
(with the mentioned coupler to radio) is a fantastic
BCDX loop antenna. It would make a great thing to
take camping away from houses and wiring, since
it packs up into a hand-reel (of 22ga) of wire, some
tape, and two fiberglass rods. You could kite-string it
from a tree and tune the continent for $5-10, plus
a pocket radio like the $10 Sony.