How does your circuit differ from the simple circuit used by AAVSO (i.e. "CAP's design")?

The original AAVSO circuit has about the same range as ours because the diodes drop and limit the upper and lower parts of the signal. We made our own minor improvements and put the detector portion (D1 & D2) of the circuit and the signal-level capacitor (C2) in a shielded box along with the opamp instead of the way done in the original AAVSO design. In the original, the long unshielded 4-conductor cable caused oscillations back to the antenna. When we redid this minor arrangement of the components to only send back DC levels across the wires, we realized considerable improvement.