N*O*R*D*IC RF modules have a 4MHz Strange..

[oigres]

hi

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??

Thank you in advance

 

[samsuffy]

With a PLL (Phase-Locked loop)

 

[oigres]

ok, with a PLL, but i must have a VCO with a frequency greater than 433MHz
am i right ? anyone could send a schematic for this?

 

[samsuffy]

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

 

[flatulent]

having a IF frequency

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.

 

[jwei363]

re

maybe they have OSC inside.

 

[flatulent]

yes they do

Here is a data sheet that shows the internal PLL and just a few external parts.
**broken link removed**