The Flex 5000 is one of those pieces of engineering for which I hold great admiration. This is quite natural. My grandfather, a true man of vision, believed strongly in taking things on and owning the issue. I worshiped him until he died before my teenage years. He often asked me, when I was half assing something if I "knew the difference between interested and committed? The chicken that gave you the egg for breakfast was interested. The pig that gave the bacon was committed!" To SDR I am committed, and the Flex Radio company is, to a large extent, responsible. My work was also strongly encouraged by my life long friend, Tom Clark, NASA astronomer, avid amateur, and a fantastic polymath.
The Flex 5000 has my fingerprints all over it. I did not pick the parts that established the circuit functionality in it, but I was most definitely involved in its design. It was a serious step towards a radio device that would meet my needs and allow me to establish certain goals for radio equipment of this type. Gerald Youngblood has been and continues to be a great friend.
Now with all of that behind us, one should never be afraid to admit that there is a thorn on the rose. The quadrature sampling detector is a marvel. It is not perfect, but its perfection is achievable in so many ways with hardware modifications and software additions, it will cause the world to sit up and take notice. It already has and it is 20 dB from its ultimate physical limits of performance.
The quadrature sampling exciter is and will be a mistake. Its imperfections, also correctable, are much more difficult to achieve for many reasons. Slight imperfections, amplified by multi kilowatt amplifiers, are glaring. These are also fixable, primarily in software, but there is no need.
Penelope and any other D/A driven digital up converter is the appropriate foundational element for excellent exciters.
I worked for hours today to put into place a fix for a wart in the 5000 QSE based exciter. It works. But again, this work is putting a band aid, albeit a brilliant one, on an existing device in an existing code base, rather than inventing the new or implementing the "known needed algorithms".
I am sure this message is getting through.