Just to give an update...

I got a response from Randy Yates in the comp.dsp group who gave me a
formula for the loop antenna signal strength which I'm including below
for reference. He said it came from the ARRL Handbook.

They dedicate an entire chapter (5) to loop antennas. Equation one
is the voltage at the loop terminals:

V = (2 * pi * A * N * E * cos(theta)) / lambda,

where

A = area of loop, in m^2
N = number of turns in loop
E = RF field strength in V/m
theta = angle between plane of the loop and the signal source
lambda = wavelength in meters.

Note that I know nothing about antennas - just acting as a scribe...
This is the expression for an untuned antenna. Shortly after this, they
provide the equation for a tuned antenna, which is identical except for
the addition of a Q in the numerator.
-- Randy Yates Digital Signal Labs http://www.digitalsignallabs.com

I did the calculations and at 100 uV/m with 50 foot of coax in a two
turn loop I get a bit over 1 uV, not so good. I'm going to see what I
can find about the signal level from ferrite cores. I had the
impression they would be lower, but I seem to recall better numbers than
this in the ones I've seen before.

Rick