For DAB Mode I, the time structure is derived from the 2048 kHz clock reference, corresponding to a DAB clock period of 1/2048 kHz = 488.28125 ns.
In some DAB literature, this value is also written as 0.48828125 µs, sometimes with fewer decimal places, but the value above—with eight digits after the decimal point in µs—is 100% correct.
(It is not an irrational number; its decimals do not continue indefinitely. But exactly ending in 5)
In the transmitter, an oscillator running at eight times this frequency (16.384 MHz) is used, and its output is divided by 8 to obtain the required time period T = 488.28125 ns. The oscillator is synchronised to the 10 MHz time base provided by the atomic clocks in the GPS satellite constellation.
- 1 ms corresponds to 2048 ticks (orthogonal symbol),
- 24 ms corresponds to 49,152 ticks (audio frames, CIF frame, ETI frame)
- 96 ms corresponds to 196,608 ticks of this clock (transmission frame).
The main 16.384 MHz oscillator has a period of approximately 61 ns, and these ticks are used to determine the value of the TIST field in the ETI frame.
The complete time structure is illustrated in the diagram below.
