IRIG timecode

Last updated September 26, 2024

Inter-range instrumentation group timecodes, commonly known as IRIG timecode, are standard formats for transferring timing information. Atomic frequency standards and GPS receivers designed for precision timing are often equipped with an IRIG output. The standards were created by the Tele Communications Working Group of the U.S. military's Inter-Range Instrumentation Group (IRIG), the standards body of the Range Commanders Council. Work on these standards started in October 1956, and the original standards were accepted in 1960.

The original formats were described in IRIG Document 104-60, later revised and reissued in August 1970 as IRIG Document 104-70, upgraded later that year as the IRIG Document to the status of a Standard, IRIG Standard 200-70. The latest version of the Standard is IRIG Standard 200-16 from August 2016.

Timecodes

The different timecodes defined in the Standard have alphabetic designations. A, B, D, E, G, and H are the standards currently defined by IRIG Standard 200-04.

The main difference between codes is their rate, which varies between one pulse per minute and 10,000 pulses per second.

IRIG timecode
Code	Bit rate	Bit time	Bits per frame	Frame time	Frame rate
A	1000 Hz	1 ms	100	0.1 s	10 Hz
B	100 Hz	10 ms	100	1 s	1 Hz
C^{[upper-alpha 1]}	2 Hz	0.5 s	120	60 s	1⁄60 Hz
D	1⁄60 Hz	60000 ms	60	3600 s	1⁄3600 Hz
E	10 Hz	100 ms	100	10 s	0.1 Hz
G	10000 Hz	0.1 ms	100	0.01 s	100 Hz
H	1 Hz	1000 ms	60	60 s	1⁄60 Hz

↑ C^{[upper-alpha 2]}^{[upper-alpha 3]} was in the original specification, but was replaced by H.
Grohman, Richard O.; Mellenbruch, Larry L.; Sowic, Felix J. (14 March 1974). Special Hardware for ARL Analysis of ACODAC Data (pdf) (Technical report). Texas University at Austin. ARL-TM-74-12. Archived from the original on 8 April 2013. Retrieved 23 December 2011.
Handbook of Time Code Formats (PDF) (Seventh ed.). Datum Inc. 1987. p. 18. Archived (PDF) from the original on 8 March 2023. Retrieved 18 March 2024– via vk7krj.com.

The bits are modulated on a carrier. A three-digit suffix specifies the type and frequency of the carrier, and which optional information is included:

Modulation type

DC level shift (DCLS) (pulse width coded without carrier)
Sine wave carrier (amplitude modulated)
Manchester modulated

Carrier frequency

No carrier (DCLS)
100 Hz (10 ms resolution)
1 kHz (1 ms resolution)
10 kHz (100 μs resolution)
100 kHz (10 μs resolution)
1 MHz (1 μs resolution)

Coded expressions

Binary-coded decimal (BCD) day of year, hours, minutes, and (for some formats) seconds and fractions are always included. Optional components are:

Year number (00–99; century is not coded)
User-defined "control functions (CF)" occupying bits not defined by IRIG
"Straight binary seconds (SBS)", a 17-bit binary counter that counts from 0 to 86399.

The types are:

BCD, CF, SBS
BCD, CF
BCD
BCD, SBS
BCD, BCD_Year, CF, SBS
BCD, BCD_Year, CF
BCD, BCD_Year
BCD, BCD_Year, SBS

The recognized signal identification numbers for each format according to the standard 200-04 consist of:

Permissible Code Formats
Format	Modulation Type	Carrier Frequency	Coded Expressions
A	0,1,2	0,3,4,5	0,1,2,3,4,5,6,7
B	0,1,2	0,2,3,4,5	0,1,2,3,4,5,6,7
D	0,1	0,1,2	1,2
E	0,1	0,1,2	1,2,5,6
G	0,1,2	0,4,5	1,2,5,6
H	0,1	0,1,2	1,2

Thus the complete signal identification number consists of one letter and three digits. For example, the signal designated as B122 is deciphered as follows: Format B, Sine wave (amplitude modulated), 1 kHz carrier, and Coded expressions BCDTOY.

The most commonly used of the standards is IRIG B, then IRIG A, then probably IRIG G. Timecode formats directly derived from IRIG H are used by NIST radio stations WWV, WWVH and WWVB.

For example, one of the most common formats, IRIG B122:

IRIG B122 transmits one hundred pulses per second on an amplitude modulated 1 kHz sine wave carrier, encoding information in BCD. This means that 100 bits of information are transmitted every second. The time frame for the IRIG B standard is 1 second, meaning that one data frame of time information is transmitted every second. This data frame contains information about the day of the year (1–366), hours, minutes, and seconds. Year numbers are not included, so the timecode repeats annually. Leap second announcements are not provided. 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. Typical commercial devices will synchronize to within 1 microsecond using IRIG B timecodes.

Timecode structure

IRIG timecode is made up of repeating frames, each containing 60 or 100 bits. The bits are numbered from 0 through 59 or 99.

At 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). The signal is disabled (carrier attenuated at least 3×, DC signal level lowered, or Manchester 0 bits transmitted), at one of three times during the bit interval:

After 0.2 of a bit time, to encode a binary 0
After 0.5 of a bit time, to encode a binary 1
After 0.8 of a bit time, to encode a marker bit

Bit 0 is the frame marker bit P_r. Every 10th bit starting with bit 9, 19, 29, ... 99 is also a marker bit, known as position identifiers P₁, P₂, ..., P₉, P₀. Thus, two marker bits in a row (P₀ followed by P_r) marks the beginning of a frame. The frame encodes the time of the leading edge of the frame marker bit.

All other bits are data bits, which are transmitted as binary 0 if they have no other assigned purpose.

Generally, groups of 4 bits are used to encode BCD digits. Bits are assigned little-endian within fields.

Bits 1–4 encode seconds, and bits 6–8 encode tens of seconds (0–59)
Bits 10–13 encode minutes, and bits 15–17 encode tens of minutes (0–59)
Bits 20–23 encode hours, and bits 25–26 encode tens of hours (0–23)
Bits 30-33 encode day of year, 35-38 encode tens of days, and bits 40–41 encode hundreds of days (1–366)
Bits 45–48 encode tenths of seconds (0–9)
Bits 50–53 encode years, and bits 55–58 encode tens of years (0–99)
Bits 80–88 and 90–97 encode "straight binary seconds" since 00:00 on the current day (0–86399, not BCD)

In IRIG G, bits 50–53 encode hundredths of seconds, and the years are encoded in bits 60–68.

Not all formats include all fields. Obviously those formats with 60-bit frames omit the straight binary seconds fields, and digits representing divisions less than one frame time (everything below hours, in the case of IRIG D) are always transmitted as 0.

No parity or check bits are included. Error detection can be achieved by comparing consecutive frames to see if they encode consecutive timestamps.

Unassigned 9-bit fields between consecutive marker bits are available for user-defined "control functions". For example, the IEEE 1344 standard defines functions for bits 60–75.

IRIG timecode

IRIG A time code structure
Bit	Weight	Meaning	Bit	Weight	Meaning	Bit	Weight	Meaning	Bit	Weight	Meaning	Bit	Weight	Meaning
00	P_r	Frame marker	20	1	Hours (0–23)	40	100	Day of year (1–366)	60	0	Unused, available for Control Functions	80	1	Straight Binary Seconds (0–86399)
01	1	Seconds (00–59)	21	2		41	200	Day of year (1–366)	61	0		81	2
02	2		22	4		42	0	Unused	62	0		82	4
03	4		23	8		43	0		63	0		83	8
04	8		24	0		44	0		64	0		84	16
05	0		25	10		45	0.1	Tenths of seconds (0.0–0.9)	65	0		85	32
06	10		26	20		46	0.2		66	0		86	64
07	20		27	0	Unused	47	0.4		67	0		87	128
08	40		28	0	Unused	48	0.8		68	0		88	256
09	P₁	Position identifier	29	P₃	Position identifier	49	P₅	Position identifier	69	P₇	Position identifier	89	P₉
10	1	Minutes (00–59)	30	1	Day of year (1–366)	50	1	Year (00–99)	70	0	Unused, available for Control Functions	90	512
11	2		31	2		51	2		71	0		91	1024
12	4		32	4		52	4		72	0		92	2048
13	8		33	8		53	8		73	0		93	4096
14	0		34	0		54	0		74	0		94	8192
15	10		35	10		55	10		75	0		95	16384
16	20		36	20		56	20		76	0		96	32768
17	40		37	40		57	40		77	0		97	65536
18	0	Unused	38	80		58	80		78	0		98	0	Unused
19	P₂	Position identifier	39	P₄	Position identifier	59	P₆	Position identifier	79	P₈	Position identifier	99	P₀	Position identifier

IRIG J timecode

IRIG standard 212-00 defines a different time-code, based on RS-232-style asynchronous serial communication. The timecode consists of ASCII characters, each transmitted as 10 bits:

1 start bit
7 data bits
1 odd parity bit
1 stop bit

The on-time marker is the leading edge of the first start bit.

IRIG J-1 timecode consists of 15 characters (150 bit times), sent once per second at a baud rate of 300 or greater:

<SOH>DDD:HH:MM:SS<CR><LF>

SOH is the ASCII "start of header" code, with binary value 0x01.
DDD is the ordinal date (day of year), from 1 to 366.
HH, MM and SS are the time of the start bit.
The code is terminated by a CR+LF pair.

At the end of the timecode, the serial line is idle until the start of the next code. There is no idle time between other characters.

IRIG J-2 timecode consists of 17 characters (170 bit times), sent 10 times per second at a baud rate of 2400 or greater:

<SOH>DDD:HH:MM:SS.S<CR><LF>

This is the same, except that tenths of seconds are included.

The full-timecode specification is of the form "IRIG J-xy", where x denotes the variant, and y denotes a baud rate of 75×2^y.

Normally used combinations are J-12 through J-14 (300, 600, and 1200 baud), and J-25 through J-29 (2400 through 38400 baud).

Combination J-xy	variant (x)	y	2^y	Baud = 75 × 2^y
J-12	1	2	4	300
J-13	1	3	8	600
J-14	1	4	16	1200

J-25	2	5	32	2400
J-26	2	6	64	4800
J-27	2	7	128	9600
J-28	2	8	256	19200
J-29	2	9	512	38400

Related Research Articles

Linear Timecode (LTC) is an encoding of SMPTE timecode data in an audio signal, as defined in SMPTE 12M specification. The audio signal is commonly recorded on a VTR track or other storage media. The bits are encoded using the biphase mark code : a 0 bit has a single transition at the start of the bit period. A 1 bit has two transitions, at the beginning and middle of the period. This encoding is self-clocking. Each frame is terminated by a 'sync word' which has a special predefined sync relationship with any video or film content.

MIDI time code (MTC) embeds the same timing information as standard SMPTE timecode as a series of small 'quarter-frame' MIDI messages. There is no provision for the user bits in the standard MIDI time code messages, and SysEx messages are used to carry this information instead. The quarter-frame messages are transmitted in a sequence of eight messages, thus a complete timecode value is specified every two frames. If the MIDI data stream is running close to capacity, the MTC data may arrive a little behind schedule which has the effect of introducing a small amount of jitter. In order to avoid this it is ideal to use a completely separate MIDI port for MTC data. Larger full-frame messages, which encapsulate a frame worth of timecode in a single message, are used to locate to a time while timecode is not running.

<span class="mw-page-title-main">Vertical interval timecode</span> Type of timecode in a video signal

Vertical Interval Timecode is a form of SMPTE timecode encoded on one scan line in a video signal. These lines are typically inserted into the vertical blanking interval of the video signal.

<span class="mw-page-title-main">Frequency-shift keying</span> Data communications modulation protocol

Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is encoded on a carrier signal by periodically shifting the frequency of the carrier between several discrete frequencies. The technology is used for communication systems such as telemetry, weather balloon radiosondes, caller ID, garage door openers, and low frequency radio transmission in the VLF and ELF bands. The simplest FSK is binary FSK, in which the carrier is shifted between two discrete frequencies to transmit binary information.

SMPTE timecode is a set of cooperating standards to label individual frames of video or film with a timecode. The system is defined by the Society of Motion Picture and Television Engineers in the SMPTE 12M specification. SMPTE revised the standard in 2008, turning it into a two-part document: SMPTE 12M-1 and SMPTE 12M-2, including new explanations and clarifications.

AES3 is a standard for the exchange of digital audio signals between professional audio devices. An AES3 signal can carry two channels of pulse-code-modulated digital audio over several transmission media including balanced lines, unbalanced lines, and optical fiber.

The Time from NPL is a radio signal broadcast from the Anthorn Radio Station near Anthorn, Cumbria, which serves as the United Kingdom's national time reference. The time signal is derived from three atomic clocks installed at the transmitter site, and is based on time standards maintained by the UK's National Physical Laboratory (NPL) in Teddington. The service is provided by Babcock International, under contract to the NPL. It was funded by the former Department for Business, Innovation and Skills; as of 2017 NPL Management Limited (NPLML) was owned by the Department for Business, Energy and Industrial Strategy (BEIS), and NPL operated as a public corporation.

WWV is a shortwave radio station, located near Fort Collins, Colorado. It has broadcast a continuous time signal since 1945, and implements United States government frequency standards, with transmitters operating on 2.5, 5, 10, 15, and 20 MHz. WWV is operated by the U.S. National Institute of Standards and Technology (NIST), under the oversight of its Time and Frequency Division, which is part of NIST's Physical Measurement Laboratory based in Gaithersburg, Maryland.

WWVB is a time signal radio station near Fort Collins, Colorado and is operated by the National Institute of Standards and Technology (NIST). Most radio-controlled clocks in North America use WWVB's transmissions to set the correct time.

JJY is the call sign of a low frequency time signal radio station located in Japan.

DCF77 is a German longwave time signal and standard-frequency radio station. It started service as a standard-frequency station on 1 January 1959. In June 1973 date and time information was added. Its primary and backup transmitter are located at 50°0′56″N9°00′39″E in Mainflingen, about 25 km south-east of Frankfurt am Main, Germany. The transmitter generates a nominal power of 50 kW, of which about 30 to 35 kW can be radiated via a T-antenna.

In a digitally modulated signal or a line code, symbol rate, modulation rate or baud rate is the number of symbol changes, waveform changes, or signaling events across the transmission medium per unit of time. The symbol rate is measured in baud (Bd) or symbols per second. In the case of a line code, the symbol rate is the pulse rate in pulses per second. Each symbol can represent or convey one or several bits of data. The symbol rate is related to the gross bit rate, expressed in bits per second.

<span class="mw-page-title-main">ALS162 time signal</span> French longwave time signal radio station

ALS162 is a French longwave time signal and standard-frequency radio station and is used for the dissemination of the Metropolitan French national legal time to the public. TéléDiffusion de France broadcast the ALS162 time signal, provided by LNE-SYRTE and LNE-LTFB time laboratories under ANFR responsibility, from the Allouis longwave transmitter at 162 kHz, with a power of 800 kW.

GPS signals are broadcast by Global Positioning System satellites to enable satellite navigation. Receivers on or near the Earth's surface can determine location, time, and velocity using this information. The GPS satellite constellation is operated by the 2nd Space Operations Squadron (2SOPS) of Space Delta 8, United States Space Force.

The pulse-code modulation (PCM) technology was patented and developed in France in 1938, but could not be used because suitable technology was not available until World War II. This came about with the arrival of digital systems in the 1960s when improving the performance of communications networks became a real possibility. However, this technology was not completely adopted until the mid-1970s, due to the large amount of analog systems already in place and the high cost of digital systems, as semiconductors were very expensive. PCM's initial goal was to convert an analog voice telephone channel into a digital one based on the sampling theorem.

IEEE 1344 is a standard that defines parameters for synchrophasors for power systems. The standard added extension to the IRIG-B time code to cover year, time quality, daylight saving time, local time offset and leap second information. IEEE 1344 was superseded by IEEE C37.118 in 2005 and the time extensions were adopted as part of the IRIG timing standard in the 2004 edition.

RBU is a time code radio station located in Moscow. It transmits a continuous 10 kW time code on 66⅔ kHz. This is commonly written as 66.66 or 66.666 kHz, but is actually 200/3 kHz. Until 2008, the transmitter site was near Kupavna 55°44′04″N38°9′0″E and used as antenna three T-antennas spun between three 150 metres tall grounded masts. In 2008, it has been transferred to the Taldom transmitter at 56°44′00″N37°39′48″E.

BPC is the callsign of a time signal broadcasting from the BPC Shangqiu Low-Frequency Time-Code Radio Station, cooperatively constructed by the National Time Service Center of the Chinese Academy of Sciences and Xi'an Gaohua Technology Co., Ltd., beginning April 25, 2002.

JN53dv is the Maidenhead grid square of an experimental shortwave time signal station in Italy. It is located in the town of Corsanico-Bargecchia near Massarosa and operated by Italcable

References

Sources

Telecommunications and Timing Group (August 2016), IRIG Serial Time Code Formats (PDF), U.S. Army White Sands Missile Range, New Mexico: Range Commanders Council, IRIG standard 200-16, archived from the original on 2018-08-26, retrieved 2024-05-27{{citation}}: CS1 maint: bot: original URL status unknown (link)
Telecommunications and Timing Group (November 2000), IRIG J Asynchronous ASCII Time Code Formats, U.S. Army White Sands Missile Range, New Mexico: Range Commanders Council, IRIG standard 212-00, archived from the original (DOC) on 2013-02-17, retrieved 2011-10-01

External links

IRIG information — IRIG information page with diagrams
The IRIGB standard site - The site dedicated to IRIGB standard Time code

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.

[CH-1] C^{[upper-alpha 2]}^{[upper-alpha 3]} was in the original specification, but was replaced by H.

[2] Grohman, Richard O.; Mellenbruch, Larry L.; Sowic, Felix J. (14 March 1974). Special Hardware for ARL Analysis of ACODAC Data (pdf) (Technical report). Texas University at Austin. ARL-TM-74-12. Archived from the original on 8 April 2013. Retrieved 23 December 2011.

[3] Handbook of Time Code Formats (PDF) (Seventh ed.). Datum Inc. 1987. p. 18. Archived (PDF) from the original on 8 March 2023. Retrieved 18 March 2024– via vk7krj.com.

[upper-alpha 1]

[upper-alpha 2]

[upper-alpha 3]

IRIG timecode

Contents

Timecodes

Timecode structure

IRIG timecode

IRIG J timecode

See also

Related Research Articles

References

Sources

External links