Time synchronization in North America

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Time synchronization in North America can be achieved with many different methods, some of which require only a telephone, while others require expensive, sensitive, and rare electronic equipment. In the United States, the United States Naval Observatory provides the standard of time, called UTC(USNO), for the United States military and the Global Positioning System, [1] while the National Institute of Standards and Technology provides the standard of time for civil purposes in the United States, called UTC(NIST).

Contents

ITU-R Standard Frequency and Time Signals

A standard frequency and time signal service is a station that operates on or immediately adjacent to 2.5 MHz, 5 MHz, 10 MHz, 15 MHz, 20 MHz, and 25 MHz, as specified by Article 5 of the ITU Radio Regulations (edition 2012). [2] The US service is provided by radio stations WWV (Colorado) and WWVH (Hawaii).

The methods below provide either Coordinated Universal Time (UTC), which is defined by Recommendation ITU-R TF.460, [3] or the official U.S. implementation of UTC, officially labeled UTC (NIST).

Internet time sources

Several different time synchronization protocols exist on the Internet, including:

ProtocolRFCsAccuracyPortsTime servers
Daytime Protocol RFC 868 Nearest secondTCP port 13
Time Protocol (a.k.a. NETDATE) RFC 868 Nearest secondTCP/UPD part 37
NTP RFC 1305, RFC 5905
SNTP RFC 1769, RFC 2030
ICMP TIMESTAMP RFC 0792, page 16
IP TIMESTAMP option RFC 0791, 3.1, page 16

GPS time synchronization

GPS receiver requirements

Utility frequency

In 2009 the Federal Energy Regulatory Commission made time error correction (TEC) of the power grid frequency mandatory. [9] While TEC does not provide full synchronization (date and time) and synchronization is lost in case of a power outage it provides an inexpensive way to maintain high long term accuracy of synchronous clocks found in most household appliances. Once the initial time is set the power grid will typically maintain the accuracy within 10 seconds relative to UTC by adjusting frequency. [10]

All time sources

Several different organizations provide publicly accessible recorded voice time sources, including the NIST Telephone Time of Day Service, see speaking clock. Other sources include GPS, terrestrial radio time signals, and internet services, as listed below.

North American Time Synchronization Sources
Time SignalTime ProvidedAccuracySourceSignal FormatHardware RequirementsLinux/Unix SoftwareWindows Software
GPS UTC(USNO)1575.42 MHz NMEA 0183 sentences, 1PPS signal.Minimum: GPS receiver that works with one's chosen software; this requires some combination of GPGGA, GPRMC, GPZDA, GPGSA, and GPGSV, sentences.

Ideal: GPS receiver (OCXO/DOCXO disciplined clock preferred) with NMEA 0183 output on RS-232 or USB, with GPZDA sentence sent at least once a second, and 1PPS signal on DCD, which includes at least these devices:

  • Gpsd plus ntpd with the GPSD NG client driver [12]
WWVB UTC(NIST)60 kHz AM IRIG "H" PWM time code with PM BPSK signal overlaid. [18] Radio-controlled clock:
  • NIST list of receivers [19]
  • AC-100-WWVB Time Receiver
  • AC-500-MSF Time Receiver
  • ClockWatch Radio Sync [20]
  • F6CTE's CLOCK [15]
WWV 2.5, 5, 10, 15, and 20 MHz AMVoice with modified IRIG-H format time code on 100 Hz sub-carrier (CCIR code)
  • HF radio and antenna (plus software if automatic updating of computer time is desired)
  • TrueTime TL-3 WWV Receiver
  • ntpd with Radio WWV Audio Demodulator/Decoder (driver can tune ICOM HF radios via C-IV)
  • COAA's Radio Clock [21]
  • F6CTE's CLOCK [15]
WWVH 5, 10, and 15 MHz AMVoice with modified IRIG-H format time code on 100 Hz sub-carrier (CCIR code)
  • HF radio and antenna (plus software if automatic updating of computer time is desired)
  • TrueTime TL-3 WWV Receiver
CHU 3.33 MHz, 7.85 MHz, 14.67 MHz Bell 103 modem tones, decodable by most computer modems
  • ntpd with Radio CHU Audio Demodulator/Decoder driver (driver can tune ICOM HF radios via C-IV)
Daytime ProtocolUTC (variant depends on server's time source)
  • ClockWatch Pro for Windows [22]
Time Protocol
Network Time Protocol pool.ntp.org Computer with NTP client that syncs at least once an hour. ntpd, sntp, ntpdate
NTPSec
Precision Time Protocol
  • Domain Time II [25]
NIST Telephone Time of Day Service [26] UTC(NIST)
  • +1-303-499-7111
  • +1-808-335-4363
Voice announcement with sync pips.Telephone connection, earn/aManual sync only.
NIST Automated Computer Time Service (ACTS) [27]
  • +1-303-494-4774
  • +1-808-335-4721
Windows computer with dialup modem.
  • ntpd with NIST/USNO/PTB Modem Time Services driver
  • ClockWatch Pro for Windows [22]
USNO Master Clock modem time [28] +1-202-762-1594Computer with Bell 212A or CCITT V.22 compatible modem
US Naval Observatory time serviceUTC(USNO)
  • +1-202-762-1401
  • +1-202-762-1069 (Washington, D.C.)
  • +1-719-567-6742 (Colorado Springs)
earn/a

See also

Related Research Articles

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<span class="mw-page-title-main">Leap second</span> Extra second inserted to keep civil time in sync with the Earths rotation

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<span class="mw-page-title-main">Radio clock</span> Type of clock which self-synchronizes its time using dedicated radio transmitters

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<span class="mw-page-title-main">WWV (radio station)</span> U.S. government shortwave radio station

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.

<span class="mw-page-title-main">WWVH</span> Radio time signal station in Kekaha, Hawaii, United States

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<span class="mw-page-title-main">JJY</span> Japanese time signal radio station

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<span class="mw-page-title-main">DCF77</span> German time signal radio station

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<span class="mw-page-title-main">Standard frequency and time signal service</span> Radiocommunication service for scientific and other purposes

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