Joel Kolstadt wrote:
"Hmm...how about...three! ground radials?"

Three radials should be fine where they are elevated to such height that
they capture all the electric lines of force from the vertical
radiator.Radials are balanced and their currents travel in offsetting
directions. The radial system does not radiate itself because of its
offsetting balances. Elevated radials must shield the earth from induced
current. This requires few radials when the radials are far above the
earth, but where the radials are near to the earth, many radials are
needed to capture all the electric lines and shield the earth from lossy
currents.

The number of radials and their effect on pattern and efficiency of
radiation from a vertical antenna is well addressed by ON4UN in
"Low-Band DXing". This is found in Chapter 9 of my 2nd edition. Choose
the efficiency and elevation angle you are willing to accept ftom the
graphs and tables presented.

Best regards, Richard Harrison, KB5WZI