Shift PLL FM transmitter frequency to Make FSK
I made research in this great forum about FSK nothing helpfull .
I have PLL FM transmitter and 9,7 kbs FSK 433.92 Mhz receiver .
I want to convert the FM transmitter to FSK by shift VCO or PLL +/- 100 Khz to make space and mark but so confused where to make this shift ?
here is a block diagram and a schematic :
I'm afraid that if i vco frequency the pll will re correct it cuz it closed loop , there is shift line in the vco what maybe it do ?
I can inject small voltage change in varactor diodes but also afriad from pll ?
how i can determent the speed of pll ic ( I mean the time need to correct the frequency if it change ) ?
best regards .
The circuit has already a FM input DEV. It should work for FSK as well. The FM input suggests that the PLL bandwidth is low enough not to work against the modulation. You would preferably use a DC-free modulation scheme, either using Manchester encoding or some kind of "whitening".
The DEV FM input is about 10Khz +/- cuz this is the bandwidth of the transmitter .
I need 200 Khz +/- ?
Why did you double the frequency shift specification? +/- 30 kHz sounds more like a reasonable range for 433 MHz band.
Anyway, if the DEV input isn't suited to achieve the intended shift, you need to modify the transmitter circuit.
My FSK 433.92Mhz receiver have a bandwidth of 200KHz , so if I use 10 Khz maybe it wont Demodulate the mark and space or what u think ?