It is obvious, that changing the RF frequency is a fundamental requirement of frequency hopping systems. Therefor programming the RF frequency is the aim of this exercise. Programming the RF frequency is done according chapter 9.1.2 of CC1200 Users Guide.
In detail, the HF $f_{RF}$ frequency is computed by:
$$ f_{RF}=\frac{f_{VCO}}{LO\ Divider} $$
where $f_{VCO}$ is the frequency of the “Voltage Controlled Oscillator (VCO)” and will be computed by $$ f_{VCO} = \frac{FREQ}{2^{16}} . f_{XOSC} + \frac{FREQOFF}{2^{18}} . f_{XOSC}$$
In this two equations $f_{XOSC}$ is the crystal frequency of the TI boards and equals to $40 MHz$. LO Divider determines the frequency band of the CC1200 and can be obtained in the FSD_BANDSELECT part of the “Frequency Synthesizer Configuration” register (FS_CFG register).
FREQ is the 24 bit VCO frequency and computed by the FREQ0 (bits 16-23 of VCO frequency), FREQ1 (bits 8-16 of VCO frequency) and FREQ2 (bits 0-7 of VCO frequency) registers. FEQOFF is intended for fine tuning the RF frequency caused by tolerances of the crystal and can be neglected.
This task requires