[zh3]

That is great stuff, many thanks for it. While not in such depth, for a precision timing network covering multiple sensors our analysis also showed that the delays and variation inherent in most higher-level radio protocols are far too high for microsecond-level synchronisation.

For this reason, we use the nRF52 radio peripheral directly (i.e. barebones C) which means we know exactly when the packet was sent and - at the other end - when it was received. Details are in the Production Specification document, which also shows how long it takes for the transmit to spin up (turn on, transmit pre-amble and so on).