Lee,

Using the loop indoors, at ground-floor level, at 20MHz, on a
groundwave path, is not inconsistent with what you get. Get it
high-up, outdoors, and it will make a big difference.

The capacitor is made from a length of coax. I wonder how long it is
and how it is located relative to the loop? Wherever it is, being
unbalanced coax it will unbalance the loop.

But what worries me, the very thin coaxial inner conductor is in
series with the main loop conductor. It may have a loss resistance
several times greater than the large diameter main loop. You could be
losing a lot of decibels.
----
Reg, G4FGQ.