Time to yell Uncle! The MHST has been relegated to the Shelf of Shame. After two months of toil, consternation, abject failure and losing some hair I am throwing in the towel. I must apologize as this could have been a pretty nifty project, but I have exhausted my tribal knowledge base and am just plain stumped as to what to try next.
Maybe at some future time I will trip over some unrelated project that suddenly like a missive from the Oracle at Delphi reveals the root cause. It is likely some simple thing -- I just don't see it.
Yesterday I fiddled and fooled with signal levels out of the I and Q channels as well as the quadrature LO level. This was to assure that each ADE-1 was not being overdriven which could result in spurs. All that did was reduce the amplitude of the spur (and the desired signal) but the spur always slightly stronger than the desired signal.
Thusly the MHST joins a host of other failed projects with a prominent place on the Shelf of Shame. It was a hairbrained idea that never made the grade. That said I remembered the urban legend story of Thomas Edison. One day a very shaken assistant came into Edison's office and said: "Sir, I have some very bad news, the storage warehouse containing many of your projects burnt down."
Edison smiled and said please repeat what you said. The assistant did so, and Edison said Thank God, and went on to say that the warehouse contained stuff that didn't work. He just didn't have the heart to rid himself of all that junk and now it was done for him. So maybe I am having an opportunity much like Edison.
Sometimes despite what you know you can't make things go. Sayonara MHST!
73's
Pete N6QW