I have posted up some more pictures of the 8568 TG project here:
/g/HP-Agilent-Keysight-equipment/album?id=78668
The pictures show kind of what it looks like so far. Also included is a comparison at 1 dB/div between flatness of the TG/8568 combo, versus typical 8568 independent flatness. The TG shot has some tilt correction applied to compensate for internal and external cable loss - it would drop about a dB lower toward the top end otherwise. The TG/8568 combo result looks a lot like the 8568 example alone, and fits within the 2 dB p-p spec.
This is for the original amplifier and leveling system, more or less - I tried to keep the new PIN leveling section compatible with the rest for now. Ultimately I expect to redo the whole thing to include the low band amplifier's directional detector, but that needs more complexity. For now, in the low band mode, the leveling is open-loop, using manually adjustable power level. Even so, it turns out to be quite good, around the same 2 dB p-p flatness, from nearly zero up to around 400 MHz. Doing true leveling all the way down to nearly DC becomes problematic, and needs an auto-tuning control loop, so that will come later. I mainly want to get it usable and more or less complete for now. Ultimately, I'd like to build a single amplifier/detector module to do the whole works, instead of the two-band system.
Ed
