![]() The bits are numbered from 0 through 59 or 99.Īt the start of each bit time, the IRIG timecode enables a signal (sends a carrier, raises the DC signal level, or transmits Manchester 1 bits). IRIG timecode is made up of repeating frames, each containing 60 or 100 bits. Typical commercial devices will synchronize to within 1 microsecond using IRIG B timecodes. Although information is transmitted only once per second, a device can synchronize its time very accurately with the transmitting device by using a phase-locked loop to synchronize to the carrier. Leap second announcements are not provided. Year numbers are not included, so the timecode repeats annually. This data frame contains information about the day of the year (1–366), hours, minutes, and seconds. The time frame for the IRIG B standard is 1 second, meaning that one data frame of time information is transmitted every second. This means that 100 bits of information are transmitted every second. IRIG B122 transmits one hundred pulses per second on an amplitude modulated 1 kHz sine wave carrier, encoding information in BCD. Timecode formats directly derived from IRIG H are used by NIST radio stations WWV, WWVH and WWVB.įor example, one of the most common formats, IRIG B122: The most commonly used of the standards is IRIG B, then IRIG A, then probably IRIG G. For example, the signal designated as B122 is deciphered as follows: Format B, Sine wave (amplitude modulated), 1 kHz carrier, and Coded expressions BCDTOY. Thus the complete signal identification number consists of one letter and three digits. The recognized signal identification numbers for each format according to the standard 200-04 consist of: "Straight binary seconds (SBS)", a 17-bit binary counter that counts from 0 to 86399.User-defined "control functions (CF)" occupying bits not defined by IRIG.Year number (00–99 century is not coded).Sine wave carrier ( amplitude modulated)īinary-coded decimal (BCD) day of year, hours, minutes, and (for some formats) seconds and fractions are always included.DC level shift (DCLS) ( pulse width coded without carrier).A three-digit suffix specifies the type and frequency of the carrier, and which optional information is included: The main difference between codes is their rate, which varies between one pulse per minute and 10,000 pulses per second.īit rate = 100 Hz = 100 × (1 / second) = 100 / second = 100 / 1000 ms = 1 / 10msīit time = 1 / (Bit rate) = 1 / (1 / 10 ms) = 10 msįrame time = (Bits per frame) × (Bit time) = 100 × 10 ms = 1000 ms = 1 secondįrame rate = 1 / (Frame time) = 1 / 1 second = 1 Hz A, B, D, E, G, and H are the standards currently defined by IRIG Standard 200-04.Ĭ was in the original specification, but was replaced by H. The different timecodes defined in the Standard have alphabetic designations.
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