Hit the issue with nothing coming out of the mixer. Using the signal injector feeding into the RF input port, I could hear RF static type noises.
So, I spoke to a few folks at the last AHARS meeting. Specifically what drive level from the LO is needed to turn on the 1N4148s. Jim, VK5TR suggests that I will need +7dB. Darryl, VK5JDS suggest about +6dB.
So I made an RF probe, a 10nF capacitor / 1N34 diode / 47M resistor style probe that I attached to the front of the DVM. A simple T shaped arrangement, on a little scrap of copper clad board and put a BNC socket on one end for a CRO probe, the other to a pair of banana plugs to attach to the DVM.
Wonderful; 0.4 volts from the LO. Now to match +7dB up to what volts output that should be...