resonance frequency

[Steph]

I think (if I have it right) that a single turn loop is seen electrically as a half wave stub antenna with one end being 0v (ground) and the other end being 'hot' at the resonant frequency,

That would be a quarter-wave-loop, which has low impedance without imaginary component, but is not in resonance. The resonant half-wave-loop has high impedance at the feeding point and the current antinode is on the opposide side of the feeding point. But in both ways, you're right, for our use it's impossible to build a loop in that dimension, since it would be kilometers

Feasible are single-turn loops with a transformer or multiturn loops. On the first, the resonance frequency depends on the trafo design, on the second on the loop design. In both cases it is not so easy to calculate the resonance frequency, because of the many variables. I have some wires here and could do a measurement if that helps. But it will work just fine if you follow the examples in the documentation. Better antenna does not neccessarily mean better locating; more important is a noise-free environment.