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[4]
ICMP TIMESTAMP	RFC 0792, page 16
IP TIMESTAMP option	RFC 0791, 3.1, page 16

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,[5] 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[6]). The Garmin GPS 18x LVC[7][8][9] 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, see speaking clock#United States.

North American Time Synchronization Sources

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: ZTI Z050 GPS dongle[10] Garmin GPS 18x OEM[7][8][9]	Gpsd plus ntpd with the GPSD NG client driver[11]	NMEATime2[12] COAA's GPSTime[13] F6CTE's CLOCK[14] ToyNTP[15] BktTimeSync by IZ2BKT[16]
WWVB	UTC(NIST)		60 kHz AM	IRIG "H" PWM time code with PM BPSK signal overlaid.[17]	Radio-controlled clock: NIST list of receivers[18] AC-100-WWVB Time Receiver AC-500-MSF Time Receiver		ClockWatch Radio Sync[19] F6CTE's CLOCK[14]
WWV			2.5, 5, 10, 15, and 20 MHz AM	Voice with modified IRIG-Hformat 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[20] F6CTE's CLOCK[14]
WWVH			5, 10, and 15 MHz AM	Voice with modified IRIG-Hformat 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 Protocol	UTC (variant depends on server's time source)						ClockWatch Pro for Windows[21]
Time Protocol
Network Time Protocol			pool.ntp.org		Computer with NTP client that syncs at least once an hour.	ntpd, sntp, ntpdate	Meinberg NTP[22] NetTime[23] ToyNTP[15] BktTimeSync by IZ2BKT[16]
NTPSec
Precision Time Protocol							Domain Time II[24]
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[25]		ClockWatch Pro for Windows[21]
NIST Telephone Time of Day Service[26]	UTC(NIST)		[phone] [phone]	Voice announcement with sync pips.	Telephone connection, ear	n/a	Manual sync only.
NIST Automated Computer Time Service (ACTS)[27]			[phone] [phone]		Windows computer with dialup modem.	ntpd with NIST/USNO/PTB Modem Time Services driver	ClockWatch Pro for Windows[21]
USNO Master Clock modem time[28]			[phone]		Computer with Bell 212A or CCITT V.22 compatible modem
US Naval Observatory time service	UTC(USNO)		[phone] [phone] (Washington, D.C.) [phone] (Colorado Springs)		ear	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

1. "US Naval Observatory Precise Time Department".
2. ITU Radio Regulations, CHAPTER II – Frequencies, ARTICLE 5 Frequency allocations, Section IV – Table of Frequency Allocations
3. "ITU-R TF.460".
4. https://ofr.ebay.com/ws/eBayISAPI.dll?EbayTime
5. "VisualGPS NMEATime2 - More Information and Help".
6. "nptd Compatible GPSes".
7. "Garmin GPS 18x OEM".
8. "Time synchronization with a Garmin GPS".
9. "Windows Serial Port GPS/PPS reference clock for NTP".
10. "ZTI Communications Z050 GPS Dongle".
11. "GPSD NG client driver".
12. "NMEATime2".
13. "GPS Time".
14. "CLOCK".
15. "Afreet Software: ToyNtp 1.2".
16. "BktTimeSync".
17. "WWVB Time Code Format".
18. "Manufacturers of Time and Frequency Receivers".
19. "ClockWatch Radio Sync".
20. "Radio Clock".
21. "ClockWatch Pro for Windows".
22. "Meinberg NTP".
23. "NetTime client".
24. "Greyware Automation Products, Inc".
25. "eBay Time".
26. "Telephone Time-of-Day Service".
27. "Automated Computer Time Service (ACTS)".
28. "USNO Master Clock modem time".

External links

• Recommendation ITU-R TF.768, Standard Frequencies and Time Signals