A dibit is a pair of bits represented by one transmitted symbol.1 In the
four-level modulations used by P25 (C4FM)
and DMR (4FSK), each of the four
symbol states maps to one of the four dibits 00, 01, 10, 11.
Each of the four C4FM/4FSK levels carries one dibit, so the bit rate is twice the symbol rate.
Overview
Because each symbol carries two bits, a four-level signal’s bit rate is twice its
symbol rate — which is why P25 Phase 1’s 4800-baud C4FM
runs at 9600 bits per second.
Sources
Dibit — Wikipedia, for the two-bits-per-symbol definition. ↩
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