IRIG-B code protocol is a commonly used serial transmission mode in time system of modern science and technology. Compared with parallel transmission mode, its physical continuity is simple, transmission distance is far, interface standardization is international.

According to the general specification of GJB2991A-2008B time code interface terminal, the actual product is extracted as follows:

The B code interface terminal provides standard frequency and time signals for measurement, control, computation, communication and other equipment to achieve time synchronization with the system.

The B code output format can be selected by national standard GJB2991A -2008 or IEEE 1344.

Product model: SYN1204 IRIG-B code generator

Code element

Each pulse in the B code is called a symbol, and the punctuality point of each symbol is the leading edge of the pulse. The repetition rate of the symbol is called the symbol rate, and the symbol rate of the B code is 100pps.

Index count

Each symbol ordinal number is determined by index technology. The index technology starts with the frame datum and counts from 0, and adds 1 to the end of the frame.

Location identifier

The width of the location identifier is 0.8 times that of the index technology interval. The location identifier P0 is ahead of the reference symbol Pr, an index technology interval, and the rest of the location identifiers (P1, P2...) appear in 10 index techniques sequentially, and the repetition rate of the location identifier is 1/10 of the code source rate.

Time coding

The time code in B code is based on UTC. The symbol of time information is called time coding. Time coding uses BCD encoding to identify the number of days, years, years and years in the year. Time code is coded by pulse width modulation. The symbol width is 0.5 times the index base interval, the symbol binary number is 1, and the pulse width is 0.2 times the index base interval, the symbol identifier binary number 0.

The number of years and the ten bits of BCD code alternatively appear in the 45~48 position of the index base, and the bits in the year appear in the same frame with even seconds. When the ten bits of the symbol 1 were in the year, the 45~48 bits of the index count represented ten bits of the year. When the ten of the year could not correspond to odd seconds, the ten place of the year was abandoned.

Leap second sign

The leap second flag is used to control the B code interface terminal to perform the leap second adjustment. The symbol of the leap second symbol is the two symbol corresponding to the index number 27 and 28. When the B UTC transmission time needs to be adjusted by backward leap seconds, the leap second flag is encoded to 01. When the forward leap second adjustment is needed, the leap second flag is encoded as 10.

Special control information

The special control information is used to issue a unified start signal to the user equipment, or send special mark signals to the user equipment to mark some special events. For the master station or independent station, the special control information is 3 symbols corresponding to index technology 76, 77 and 78.

amplitude modulation

The amplitude of the B code is modulated by the forward wave. The frequency of the sine wave is closely related to the symbol rate, which is ten times the symbol rate. At the same time, the orthogonal zero crossing of the sine wave is consistent with the front edge of the modulated format symbol.