Tom, Hook the 53132A calibrator that I sent you and check one of the calibrator outputs for signal goodness. It uses the sine-square circuit in the LPRO-101 manual (input cap connected to center of a 39K/39K voltage divider connected to a 74HC gate (74AC gates have some advantages and disadvantages here). It's the simplest excellent bang-for-the buck squarer (three passives and a single CMOS gate). You can use single-gate chips. I'm using the same circuit on the LPFRS/LPRO/OCXO interface board. I'm also pondering doing a small board with a sine/square wave input, square wave output, PICDIV, PICPET, and a 10 MHz square to sine filter. Attached is the xDEV plot of the calibrator (using TAPR-TICC, TADD2-mini, 5071A reference).