The SFD delay should be fairly constant after the issue of the STXON strobe using the CSP, the delay is a few microseconds .
From User's Guide:
Transmission of preamble begins 192 μs after the STXON or STXONCCA command strobe. This is
referred to as TX turnaround time in [1]. There is an equal delay when returning to receive mode.
When returning to idle or receive mode, there is a 2-μs delay while the modulator ramps down the signals
to the DACs.
The down ramping happens automatically after the complete MPDU (as defined by the
length byte) has been transmitted or if TX underflow occurs. This affects:
• The SFD signal, which is stretched by 2 μs.
• The radio FSM transition to the IDLE state, which is delayed by 2 μs.
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