Looking at the radio section of the nrf52832 data sheet I see that in section 21.1.2 Packet configuration it is stated that "For all modes that can be specified in the MODE register, the PREAMBLE is one byte long."
However, in section 21.2.12 PCNF0 (the description of the PCNF0 register) the description for the PLEN field is
G RW PLEN Length of preamble on air. Decision point: Registers on page 208 task 8bit 0 8-bit preamble 16bit 1 16-bit preamble
which seems to suggest that a 2 byte preamble is possible.
Which is correct ?