I've been incrementally stuffing and testing the controller board. First was the power supply section; it works fine. The 10V intermediate rail came right up, and from that the 5V rail was trivial. The 8V rail required that I force the 8V rail enable transistor (doh - should have had a test point there) Q5 on. I trimmed that rail to 8V without issue. Not tested is the 24V high-side switch; need to find the chip in my messy shop.

Next, I stuffed the 10 MHz distribution circuitry. This is a 2-way splitter right from the 10 MHz Rb oscillator. One branch (the "analog branch") gets amplified up and then fed into a 4-way splitter. The other branch (the "digital branch") gets Z matched to about 1.5K ohms and fed into a 74AC08 gate to convert from sine to square. I used my HP 8660 sweeper to feed in a 10 MHz test signal at -20dBm, and used my HP 8557 spectrum analyzer to check levels along the analog path. Then increased the power to +13 dBm (about the same as the Rb oscillator) and saw that I was getting the expected levels at all four outputs of the final passive splitter. The digital branch is working, also, but I think I'd like to play with the DC level to get the duty cycle on the 10 MHz square output closer to 50%.

It's hard to test the comb generator without the microcontroller up and running, so I'll focus on the micro next. The comb generator needs an 8:1 multiplexor forced to select the comb rate (100kHz ... 10 MHz) so that's the holdup there. So, next steps are getting the control program written to allow switches to turn on/off outputs, etc.