Ian Drummond described something like this in an early issue of CREGJ.  I will 
see what I can find.

John G3PAI

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On 15/03/2005 at 09:01 Andy wrote:

Can anyone recall this equation, I know it was mentioned on this
reflector before...

What is the output voltage for an untuned small loop into an arbitrarily
high impedance?  It is proportional to H, and presumably F^2, and I seem
to recall it is an absolute value, virtually un-influenced by losses,
conductor diameter etc.  Therefore can be used for accurate H field (and
hence far field radiation) signal strength measurements.

Andy  G4JNT