As know, FSK and OOK are the modulation types that can be configured in the radio by setting the bits 4-3 from the RegDataModul register, as shown in below picture taken from Reference Manual:
A common inquire you could have is: what modulation should I use? Let's first understand how these modulations work.
Frequency Shift Keying is a modulation type that uses two frequencies, for 0 and 1.
In a spectrum analyzer we can see a spectrum similar to the next picture, where the frequency for 0's is separated from the central frequency with FDev, and same case for the frequency for the 1's:
On Off Keying is a modulation type that represents a logic 1 with the presence of the carrier frequency and a logic 0 with the absence of it.
In a spectrum analyzer we can see a spectrum similar to the next picture, where the central frequency represents a logic 1. We can not see a logic 0 in the spectrum due to it's represented as the absence of power.
Then what modulation should I use?
FSK is most commonly used because is more spectral efficient so has better sensitivity.
In the other hand, OOK modulation is commonly used in applications where the frequency accuracy can not be guaranteed. It also helps in conserving battery power due to the power absence for the logic 0's.