This manual was very clear and complete, the prices can't be beat, great to have older manuals available!
Text excerpt from page 56 (click to view)
GEX-P900DAB
3) Guard interval The time 25% more than the sampling time required for processing DAB signals by FFT is called "guard interval." For multipath within the time of guard interval, errors can be corrected in most cases, regardless of the D/U ratio. Mode 1 2048 points (1 ms): Number of samples required for FFT 512 points (250 µs): Guard interval
Delayed multipath wave S1 S2 Actual DAB signal S1 S2 Direct wave (OFDM wave)
Interference between different symbols (effect of delay) Time required for FFT (1 ms)
Guard interval (250 µs)
S1
S2 Received DAB signal
Time required for FFT for every symbol
The time of guard interval depends on modes. Different time of guide interval is used for transmitting frequency, receiving speed (vehicle speed), etc.
