IEN Codified RAI signal

The text and the figures of this page are reproduced and translated from an italian publication of the National Electrotecnical Institute "G. Ferraris" (IEN).

Technical description

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

• S1 = first 32 bits segment
• S2 = second 16 bits segment
• RP = reference acoustic pulses

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

• ID = code segment identifier
• OR = hours (tens and units)
• MI = minutes (tens and units)
• OE = day-light saving time (1), solar time (0)
• P1 = parity for the first part of the segment
• ME = month (tens and units)
• GM = day of month (tens and units)
• GS = day of week (1 = Monday)
• P2 = parity for the second part of the segment

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 1^st 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

• ID = code segment identifier
• AN = year (tens and units)
• SE = forewarning of time change solar/day-light saving
  111 : no change within 7 days
  110 : change within 6 days
  ...
  001 : change within 1 day
  000 : at 02:00 comes day-light saving time or at 03:00 comes back solar time.
  
• SI = leap second forewarning
  00 : no leap second this month
  01 : 1 leap second added at the end of the month
  11 : 1 leap second subtracted at the end of the month
  
• PA = parity

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.