CC1200 frame format

From the CC1200 User Guide (www.ti.com/lit/swru346)

page 83: number of preamble bytes from 0.5 bytes to 30 bytes. 0.5 byte preamble (4 bits) is sufficient unless you use FB2PLL feature (see User Guide for description). Then the minimum is 4 bytes.

page 81: number of sync word bits is 11, 16, 24, or 32. The sync word detection circuitry is very robust so even 11 bits will give robust performance (i.e. limited false sync word detection). We use 4 bytes sync word in our SW examples.

The above is if you use the packet handling features in CC1200. If you have other sync word length you can disable the automatic sync word insertion and instead write the sync word to the TX FIFO before transmitting the data.

Check 6.7 in the UserGuide and the register description for SYNC_CFG1.

PREAMBLE_CFG1 sets the predefined preamble lengths, others are possible.