Re: Need help with Telemetry/ Data transmission thru FM or
An easy way for FSK modulation is to inject the data into the PLL loop filter. The data must be scrambled (DC free, no long strings of 1 or 0) and you can do this with 4B5B encoding, manchetser encoding, or a PRN code.
There are some fractional-N PLLs that lock fast enough so the divider registers can be toggled to produce FSK so you can go down to DC, but the data slicer on the RX side will still be AC coupled so you'll still need scrambling.
For receiving I'd use one of the FSK receiver ICs that has built in mixer, limiters, discriminator, and data slicer. Of course you'll need a PLL too for the recieve LO, and a micro-controller to do clock recovery and de-scrambling.
All this can be done in FPGAs too but that would be wasted resources wasted on FSK.