The CN0239 document states that the circuit works as either a UP or a DOWN converter. In fact, EVERY frequency indication, including the graphs all indicate performance up to 4 GHz. However, the output transformer, TC4-1W+, is rated for 3 to 800 MHz.
Can you verify if the Upconvert mode only works from 3 to 800 MHz ??
If I am correct, please add notes in the Diagram to show the IF output frequency limit, since that would apply to both the UP and the DOWN converter modes of operation.
Regards, Jim Pennell