The text and the figures of this page are reproduced and translated from an italian publication of the National Electrotecnical Institute "G. Ferraris" (IEN).
The time signal generated by IEN and broadcasted by RAI (the public
radio and television broadcaster of Italy) consists of a date code divided
into two segments of binary data, starting at seconds 52 and 53, and of
six acoustic pulses starting at seconds 54, 55, 56, 57, 58 and 00 of each
minute. Figure 1 shows the timing scheme of the several parts forming the
Codified RAI Signal (SRC). The six acoustic pulses, that formed the old
version of the signal before the introduction of the date code, consist
of 100 sinusoidal cycles at 100 Hz; each pulse has a duration of 100 milliseconds.
The date code is formed by a first segment of 32 bits of data, starting at second 52 and by a second segment of 16 bits of data starting at second 53 of each minute, the two segments last respectively 960 and 460 milliseconds. The binary coding is obtained inserting a 2000 Hz tone for each logical level "0" and a 2500 Hz tone for each logical level "1", one tone has a duration of 30 milliseconds.
Fig. 1 - Comprehensive Diagram of codified RAI signal
The first segment of code begins with the two identification bits "01". The parity bits (odd parity) are put in the middle and at the end of the segment. The segment carries the hours (from 0 to 23), the minutes, the month number, the day number of month, the day number of week, the type of time: solar time (Central Europe mean Time) or day-light saving time.
Fig. 2 - Diagram of the first segment (S1) of Codified RAI Signal
The second segment of code begins with the two identification bits "10", making it different from the first one. A parity bit (odd parity) is put at the end of the segment. The segment carries the year (tens and units), the forewarning of change from solar time to day-light saving time or viceversa, in advance of six days, the forewarning of leap second insertion. Figures 2 and 3 shows the signal coding at 19:26:52 of Sunday, May 1st 1994, with day-light saving time and without any forewarning about time change or leap second insertion.
Fig. 3 - Diagram of the second segment (S2) of Codified RAI Signal
The signal is generated every minute by IEN and it is generally broadcasted before the news by RAI; the mean number of daily broadcasts is 15-25 for each radio network and 2-3 for each television network. The user receives this signal with a maximum delay (in Italy) of about 12 milliseconds, while the synchronization accuracy is better then 1 millisecond.