Some N*O*R*D*IC RF modules have a 4MHz crystal but they send and receive information with a 433MHz frequency.
How is this possible? how can i get a 433MHz signal with a 4MHz crystal oscillator as reference??
the input of a VCO is a voltage ...
not a frequency...
I have no quick schematics...
as an little overview:
a PLL needs 4 blocs :
- a VCO : produce your final frequency
- a frequency divider : divide the final frequency to be equal to your ref freq
- a phase comparator : to produce a signal "proportional" to the difference between the ref and the divided freq
- a filter : to produce the voltage for the VCO
a quick look on google for PLL schematic should help you
It looks like this could be a superhetrodyne system. The IF frequency is selected to make the on the air frequency 433.936 even though the local oscillator is a multiple of 4.