Time synchronization in North America
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).
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 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:
Protocol | RFCs | Accuracy | Ports | Time servers |
---|---|---|---|---|
Daytime Protocol | RFC 868 | Nearest second | TCP port 13 | |
Time Protocol (a.k.a. NETDATE) | RFC 868 | Nearest second | TCP/UPD part 37 | |
NTP | RFC 1305, RFC 5905 | |||
SNTP | RFC 1769,RFC 2030 | |||
eBay time |
GPS time synchronization
GPS receiver requirements
- Minimum: GPS receiver that works with your chosen software; this requires some combination of GPGGA, GPRMC, GPZDA, GPGSA, and GPGSV sentences. This provides accuracy of between 1 and 2 seconds, and includes most, but not all modern GPS receivers.
- Better: USB GPS receiver with the NMEA 0183 GPZDA sentence sent at least once a second. The developer of the Windows software NMEATime2 recommends GPS units with the U-blox 7 receiver,[4] and this software uses a control loop to analyze the text of the GPS timing sentence, and claims to achieve 1 ms accuracy with the technique.
- Better yet: RS-232 GPS receiver with the NMEA 0183 GPZDA sentence sent at least once a second, plus a 1PPS signal on DCD (1 μs accuracy possible with a real RS-232 port not on the USB bus; 1 ms possible with a RS-232 to USB adapter[5]). The Garmin GPS 18x LVC[6][7][8] appears to be the only such device that is generally available to consumers, but this then needs an external 5 V DC power source.
- Best: Higher accuracy is possible with a high-end GPS receiver designed for time signal use, but these are very expensive (around $1000), feature OCXOs (oven-controlled crystal oscillators), and often require special software and physical RS-232 ports not connected via a USB bus to achieve that accuracy.
Telephone time sources
Several different organizations provide publicly accessible recorded voice time sources, including the NIST Telephone Time of Day Service,
Time Signal | Time Provided | Accuracy | Source | Signal Format | Hardware Requirements | Linux/Unix Software | Windows 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: |
|||
WWVB | UTC(NIST) | 60 kHz AM | IRIG "H" PWM time code with PM BPSK signal overlaid.[16] | Radio-controlled clock:
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WWV | 2.5, 5, 10, 15, and 20 MHz AM | Voice with modified IRIG-Hformat time code on 100 Hz sub-carrier (CCIR code) |
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WWVH | 5, 10, and 15 MHz AM | Voice with modified IRIG-Hformat time code on 100 Hz sub-carrier (CCIR code) |
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CHU | 3.33 MHz, 7.85 MHz, 14.67 MHz | Bell 103 modem tones, decodable by most computer modems |
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Daytime Protocol | UTC (variant depends on server's time source) |
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Time Protocol | |||||||
Network Time Protocol | pool.ntp.org | Computer with NTP client that syncs at least once an hour. | |||||
NTPSec | |||||||
Precision Time Protocol |
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eBay protocol | San Jose, CA local time | HTTP | Computer with Web browser and TCP port 80 open for HTTP traffic and able to reach the eBay Time page[24] |
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NIST Telephone Time of Day Service[25] | UTC(NIST) |
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Voice announcement with sync pips. | Telephone connection | n/a | Manual sync only. | |
NIST Automated Computer Time Service (ACTS)[26] |
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Windows computer with dialup modem. |
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USNO Master Clock modem time[27] | +1-202-762-1594 | Computer with Bell 212A or CCITT V.22 compatible modem | |||||
US Naval Observatory time service | UTC(USNO) |
|
n/a |
See also
- Time signal
- Atomic clock
- Network time protocol
- Radio clock
- List of radio time signal stations
- WWV (radio station)
- WWVH
- WWVB
- Extended Data Services (XDS "Time-of-Day Packet")
- Standard frequency and time signal service
- Coordinated Universal Time
- List of UTC timing centers
- Time transfer
- Time and frequency transfer
- Time synchronization
- Time synchronization over radio
References
- ^ "Department of the Navy Time Serice Department".
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(help) - ^ ITU Radio Regulations, CHAPTER II – Frequencies, ARTICLE 5 Frequency allocations, Section IV – Table of Frequency Allocations
- ^ "ITU-R TF.460".
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(help) - ^ "VisualGPS NMEATime2 - More Information and Help".
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(help) - ^ "nptd Compatible GPSes".
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(help) - ^ a b "Garmin GPS 18x OEM".
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(help) - ^ a b "Time synchronization with a Garmin GPS".
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(help) - ^ a b "Windows Serial Port GPS/PPS reference clock for NTP".
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(help) - ^ "ZTI Communications Z050 GPS Dongle".
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(help) - ^ "GPSD NG client driver".
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(help) - ^ "NMEATime2".
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(help) - ^ "GPS Time".
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(help) - ^ a b c "CLOCK".
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(help) - ^ a b "Afreet Software: ToyNtp 1.2".
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(help) - ^ a b "BktTimeSync".
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(help) - ^ "WWVB Time Code Format".
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(help) - ^ "Manufacturers of Time and Frequency Receivers".
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(help) - ^ "ClockWatch Radio Sync".
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(help) - ^ "Radio Clock".
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(help) - ^ a b c "ClockWatch Pro for Windows".
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(help) - ^ "Meinberg NTP".
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(help) - ^ "NetTime client".
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(help) - ^ "Greyware Automation Products, Inc".
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(help) - ^ "eBay Time".
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(help) - ^ "Telephone Time-of-Day Service".
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(help) - ^ "Automated Computer Time Service (ACTS)".
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(help) - ^ "USNO Master Clock modem time".
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