Editing IRIG timecode (section)

== 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.

{|class="wikitable sortable"
|+IRIG timecode
! Code || Bit rate || Bit time || Bits per frame || Frame time || Frame rate
|-
! A
| 1000&nbsp;Hz || 1 ms || 100 || 0.1 s || 10&nbsp;Hz
|-
! B
| 100&nbsp;Hz || 10 ms || 100 || 1 s || 1&nbsp;Hz
|- style="text-decoration:line-through"
! C{{efn-ua|name=CH}}
| 2&nbsp;Hz || 0.5 s || 120 || 60 s || {{frac|60}}&nbsp;Hz
|-
! D
| {{frac|60}}&nbsp;Hz || 60000 ms || 60 || 3600 s || {{frac|3600}}&nbsp;Hz
|-
! E
| 10&nbsp;Hz || 100 ms || 100 || 10 s || 0.1&nbsp;Hz
|-
! G
| 10000&nbsp;Hz || 0.1 ms || 100 || 0.01 s || 100&nbsp;Hz
|-
! H
| 1&nbsp;Hz || 1000 ms || 60 || 60 s || {{frac|60}}&nbsp;Hz
|}

{{notelist-ua|name=CH|refs=
{{efn-ua|name=CH|C<ref>{{cite tech report |url=https://apps.dtic.mil/sti/pdfs/ADA000295.pdf |archive-url=https://web.archive.org/web/20130408112407/http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA000295 |url-status=live |archive-date=April 8, 2013 |format=pdf |title=Special Hardware for ARL Analysis of ACODAC Data  |first1=Richard O. |last1=Grohman |first2=Larry L. |last2=Mellenbruch |first3=Felix J. |last3=Sowic |date=1974-03-14 |publisher=Texas University at Austin |id=ARL-TM-74-12 |access-date=2011-12-23 | df = dmy-all }}</ref><ref>{{cite book | title = Handbook of Time Code Formats | url = http://www.vk7krj.com/ham_stuff_pics/Handbook_of_Time_Code_Formats.pdf | publisher = Datum Inc. | edition = Seventh | year = 1987 | page = 18 | access-date = 2024-03-18 | archive-url = https://web.archive.org/web/20230308040915/https://www.vk7krj.com/ham_stuff_pics/Handbook_of_Time_Code_Formats.pdf | archive-date = 2023-03-08 | url-status = live | via = vk7krj.com | df = dmy-all}}</ref> was in the original specification, but was replaced by H.}}
}}

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:
<ol start=0 type=1>
<li>[[Direct current|DC]] level shift (DCLS) ([[Pulse-width modulation|pulse width coded]] without carrier)</li>
<li>Sine wave carrier ([[amplitude modulated]])</li>
<li>[[Manchester code|Manchester]] modulated</li>
</ol>

;[[Carrier frequency]]:
<ol start=0 type=1>
<li>No carrier (DCLS)</li>
<li>100&nbsp;Hz (10 ms resolution)</li>
<li>1&nbsp;kHz (1 ms resolution)</li>
<li>10&nbsp;kHz (100 μs resolution)</li>
<li>100&nbsp;kHz (10 μs resolution)</li>
<li>1&nbsp;MHz (1 μs resolution)</li>
</ol>

;Coded expressions
:[[Binary-coded decimal|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:<ol start=0 type=1><!--
--><li>BCD, CF, SBS</li><!--
--><li>BCD, CF</li><!--
--><li>BCD</li><!--
--><li>BCD, SBS</li><!--
--><li>BCD, BCD_Year, CF, SBS</li><!--
--><li>BCD, BCD_Year, CF</li><!--
--><li>BCD, BCD_Year</li><!--
--><li>BCD, BCD_Year, SBS</li><!--
--></ol>

The recognized signal identification numbers for each format according to the standard 200-04 consist of:
{| class="wikitable" border="1"
|+ 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&nbsp;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 station]]s [[WWV (radio station)|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&nbsp;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.