My doubler circuit is just a 74HC86. One gate connects to the input 10 MHz signal and is used as the squarer / buffer. I'm using the squarer from the LPRO-101 manual / Wenzel web site. It can be configured as either version shown in the LPRO manual, or a hybrid of the two. Two gates are used as a delay line. The squared signal and the delayed signal go the 4th XOR gate. The output is a narrow pulse that clocks a 74AC74 D flip flop to get complementary 10 MHz outputs.