frequency fref 1 of the first time based oscillator 16 is selected to occur so that spurs 30 occur at different locations than the spurs 35 of oscillator 18 operating at fref 2 by using different fref 1 and fref 2 values and corresponding frequency division values nw and nf df the output frequency fo boundary spurs 30 shown in fig2 a in hashed lines can be pushed over in frequency far enough to avoid spurs 35 in fig2 b to let the phase locked loop entire circuit of fig1 reject them in one embodiment the time base 16 is selected by switch 20 while the switch 20 is transitioned to connect time base 18 at frequencies where spurs 30 occur a controller 22 is programmed to control the switch 20 as well as the frequency division values nw and nf df in frequency dividers 12 and 14 to provide a range of frequencies fo without encountering spurs the controller can also vary the frequency f osc of oscillator 2 which in exemplary circuitry can be set from 1 5 3 ghz the controller can be a microprocessor digital signal processor or other control device that can store control software and provide signals to control external devices of the phase locked loop programming of the controller can be done to avoid frequency spurs while providing a desired frequency spectrum for the synthesizer output fo fig3 illustrates how frequency values can be calculated to enable selection of time base reference frequencies and other values for the circuit of fig1 to push spurs out of range first of all the spurs are identified by hatched lines along an amplitude vs frequency plot the unacceptable.