[Raleigh]

It should be insulated, just a length of hook-up wire. It doesn't really matter what kind. You could use uninsulated wire, but then you'd have to be careful not to touch the coils together or touch anything live.

Yes, that 6 inch loop is essentially the same thing I'm suggesting. I don't think the dimensions or the shape are too critical. I made one from some scrap plywood about 6" by 6". I put a couple of small holes in the board, wrapped 4 turns of insulated wire around it about 1/4 inch apart, ran the wire through the holes and held it in place by tying knots in the wire so it would stay put. One end of the wire is unconnected to anything. The other goes to the signal generator through a .01 uF capacitor.

For this test you don't need the capacitor, but any time you attach the signal generator to any part of a radio you should isolate it with a capacitor. Often the alignment instructions will say so.

P.S. Mine is stranded, 20 ga., but I don't think it matters. Stranded is a little easier to tie knots in, but you could use tape or glue or tacks, or anything to hold the wire in place.