This generator from Rohde & Schwarz works from 100Khz at 1GHz. The generation of signals is made by three VCO whose operating ranges are nested into each other over the entire operating range of the equipment.

This is a trick for the generation of RF signals over a wide operating range but it slightly complicates the repair of a classic failure of this device : the loss of lock on one or more PLL that drive the three VCO.

I had to readjust these VCO twice in 5 years. Indeed, the VCO drift with use to a point where the PLL is no long able to hang. At this time, the generator reports an lock error and does not generate anything (or in some cases a free signal on a different frequency that the one set on the front panel).

To resolve this problem, this is how I did it :



In doing so, we get a few years of operation with a good signal generation across the range of use of SMX.