"Owen" wrote
Reg, I mentioned in an earlier post that I was concerned about the
estimate of the loop inductance.

Owen,

The HF inductance of a square loop is -

L = 0.8 * H * ( Ln( 4 * H / D ) - 1.467 ) microhenries,

where H is length of one side,

and D is diameter of circular conductor,

both dimensions are in metres.

There are half a dozen other formulas which at first appear to be
different from the above but can be mathematically transformed to be
identical. And then there are imperial and metric units.

I got it out of one of one of my old notebooks. It's what I use in my
programs. I think I stole it from Terman. And Terman stole it from
Grover. So it's sure to be accurate enough for anything you are ever
likely to use it for.

It is obviously an approximation because when a large conductor
diameter is comparable with a very short length of side, the
inductance has a negative value.

As a sanity check, compare it with whatever formula you have used up
to now.
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Reg, G4FGQ