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IRIG-B time code: formats, connection and use

IRIG-B is the standard time code for timing over coax. What do B00x and B12x mean, which connection do you use, and when do you choose IRIG over NTP or PTP?

Choose your reading level

IRIG-B is a time code: a signal that carries the exact time over a simple cable (usually coax). Where NTP and PTP work over a network, IRIG-B sends the time as an analogue or digital signal, ideal for measurement equipment, defence and industrial systems that need a direct time reference without a network.

The code exists in variants: the number (B000, B120, B122...) indicates whether the signal is digital or modulated and what information it carries. The most common are the unmodulated DCLS variant (B00x) and the amplitude-modulated variant (B12x) over coax.

Unsure whether you need IRIG, NTP or PTP? We are glad to help. Ask for advice.

IRIG-B is the most common time code for distributing time over a direct connection (coax), independent of an IP network. This guide explains the formats, how you connect, and when to choose IRIG over NTP or PTP.

What is IRIG-B?

IRIG (Inter-Range Instrumentation Group) is a family of time codes; IRIG-B is the variant that broadcasts a full timestamp once per second. It is widely used in measurement systems, defence, energy and broadcast where devices need a common time without the complexity of a network.

The formats (the number)

The IRIG-B number describes the shape and content of the signal:

B00x (unmodulated, DCLS): a digital pulse signal, usually over a separate line. Accurate and simple.
B12x (amplitude-modulated): a 1 kHz carrier over coax, suitable for longer distances.
The last digits indicate which extra information (year, control bits, straight binary seconds) is carried.

Connection

IRIG-B usually runs over coax (BNC) for the modulated variant, or over a twisted pair for the DCLS variant. Mind cable length, termination and grounding: as with an antenna, the weakest link determines quality.

IRIG, NTP or PTP?

IRIG-B: direct time distribution without a network, ideal for measurement equipment and legacy systems.
NTP: time over an IP network, millisecond accurate. See NTP vs PTP.
PTP: time over an IP network, sub-microsecond.

Many installations combine them: a grandmaster provides both PTP/NTP and an IRIG-B output.

Masterclock and IRIG-B

Our GMR grandmasters and time-code products deliver and process IRIG-B. Not sure which output you need? Tell us your setup.

IRIG-B encodes a full timestamp in a 1-second frame, with or without 1 kHz amplitude modulation. The choice between DCLS (B00x) and AM (B12x) is a trade-off between accuracy and distance/cable convenience.

Frame and modulation

An IRIG-B frame contains 100 bits per second (10 ms per bit), encoded via pulse width: index count, position identifiers, BCD time (seconds to days), optional year and straight binary seconds (SBS). The DCLS variant (B00x) provides the sharpest edge and therefore the best accuracy; the AM variant (B12x) modulates the same code on a 1 kHz carrier, easing transport over coax and longer distances at the cost of demodulation uncertainty.

Accuracy and chain

The achievable accuracy depends on cable delay, termination and demodulation. For DCLS the determining factor is edge detection; for AM the zero-crossing detection of the carrier. Compensate known cable delays where the application requires it.

Position in the time chain

IRIG-B is usually an output of a disciplined grandmaster (GNSS-disciplined, traceable to UTC). The code itself carries no uncertainty budget; the traceability comes from the source. See GNSS disciplining and stratum levels.

Migration

Many legacy installations run on IRIG-B. When modernising, an IRIG-B output is often still needed alongside NTP/PTP; choose a grandmaster that provides both. See replacing your time server.

Sources: IRIG Standard 200 (Range Commanders Council); IEEE 1588-2019; NIST Time & Frequency Division.