Time from NPL (MSF): Difference between revisions
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The '''National Physical Laboratory time signal''' is a broadcast from the [[Rugby VLF transmitter]] near [[Rugby, Warwickshire]] based on [[time standard]]s maintained by the British [[National Physical Laboratory, UK|National Physical Laboratory]]. The transmitted signal has an [[effective radiated power]] of 15 [[kilowatt|kW]], on a frequency of 60 [[kHz]], the same frequency used by [[WWVB]]. |
The '''National Physical Laboratory time signal''' is a broadcast from the [[Rugby VLF transmitter]] near [[Rugby, Warwickshire]] based on [[time standard]]s maintained by the British [[National Physical Laboratory, UK|National Physical Laboratory]]. The transmitted signal has an [[effective radiated power]] of 15 [[kilowatt|kW]], on a frequency of 60 [[kHz]], the same frequency used by [[WWVB]]. The signal strength is greater than 10 mV/m at 100 km and greater than 100 μV/m at 1000 km from the transmitter. The signal is widely used in northern and western Europe. The carrier frequency is maintained at 60 kHz to within 2 parts in 10<sup>12</sup>. |
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The transmitter’s [[callsign]] is MSF. It is not an abbreviation: ‘M’ is one of the [[ITU prefix|prefixes]] allocated to the [[United Kingdom]], and the letters 'SF' were randomly allocated. However, [[General Post Office|Post Office]] staff that operated the station in 1951 insist that the name derives from the Modulated Standard Frequency scientific reference transmissions started in that year. |
The transmitter’s [[callsign]] is MSF. It is not an abbreviation: ‘M’ is one of the [[ITU prefix|prefixes]] allocated to the [[United Kingdom]], and the letters 'SF' were randomly allocated. However, [[General Post Office|Post Office]] staff that operated the station in 1951 insist that the name derives from the Modulated Standard Frequency scientific reference transmissions started in that year. |
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==Protocol== |
==Protocol== |
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Signal is transmitted at one bit per second, where a long pulse (200 ms) is 1 and a short pulse (100 ms) is 0. The entire message is 43 [[bit]]s long, and starts on the 17th second of each minute. Each field is coded in [[Binary numeral system|binary]], with the [[most significant bit]] earliest. [[DUT1]] is sent in seconds one through sixteen inclusive past the minute, by using two short pulses per second for each tenth of a second of the value of DUT1, and encoding the sign of DUT1 by putting the double pulses in seconds one to eight for positive, and seconds nine to sixteen for negative. |
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[[Image:Time_signal.jpg]] |
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{| border=1 |
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|- |
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!Field |
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!Length |
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!Starting in the |
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!Range |
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|- |
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| Year |
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| 8 bits |
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| 17th second |
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| 00-99 |
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|- |
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| Month |
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| 5 bits |
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| 25th second |
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| 1 (January) - 12 (December) |
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|- |
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| Day |
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| 6 bits |
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| 30th second |
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| 1-31 |
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|- |
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| Weekday |
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| 3 bits |
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| 36th second |
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| 0 (Sunday) - 6 (Saturday) |
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|- |
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| Hour |
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| 6 bits |
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| 39th second |
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| 0-23 |
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|- |
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| Minute |
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| 7 bits |
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| 45th second |
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| 0-59 |
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|- |
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| [[Magic number (programming)|Magic number]] |
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| 8 bits |
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| 52nd second |
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| = 126 (01111110 in binary) |
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|} |
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The [[MSF]] time and date code format is summarised in the diagrams above. Simple on-off carrier modulation is used, the rise and fall times of the carrier are determined by the combination of antenna and transmitter. The timing of these edges is governed by the seconds and minutes of [[Coordinated Universal Time]] (UTC), which is always within a second of [[Greenwich Mean Time]] (GMT). Every UTC second is marked by an 'off' preceded by at least 500 ms of carrier, and this second marker is transmitted with an accuracy better than ±1 ms. |
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Notes |
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* Centuries are not represented in this transmission |
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The first second of the minute begins with a period of 500 ms with the carrier off, to serve as a [[minute]] marker. The other 59 (or, exceptionally, 60 or 58) [[seconds]] of the minute always begin with at least 100 ms 'off' and end with at least 700 ms of carrier. Seconds 01-16 carry information for the current minute about the difference (DUT1) between atomic and astronomical time, and the remaining seconds convey the time and date code. The time and date code information is always given in terms of UK clock time and date, which is UTC in winter and UTC+1h when Summer Time is in effect, and it relates to the minute following that in which it is transmitted. |
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* The 1s in the magic number can contain additional information, by encoding 0 as 200 ms 0, and 1 as 300 ms: |
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** Bits 54-57 are checksums |
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Bits 17B-*51B inclusive, and bits 01A-*16A inclusive, are currently set to '0', but may be used in the future. Bits *52B and *59B are currently set at '0' but they may be used in the future. |
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** Bit 58 is 1 during [[British Summer Time]] and 0 during [[Greenwich Mean Time]] |
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* The number of [[second]]s in a [[minute]] can be between 59 and 62, so a [[leap second]] will typically not be noticed until at least 17 seconds after it happens |
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'''Minute Identifier''' |
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* Consumer clocks typically update once an hour from this signal, and use a standard [[quartz]] crystal to keep time between updates or when the signal is unavailable. |
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Bits *53A, *54A, *55A, *56A, *57A and *58A are all set permanently at '1', and are always preceded by bit *52A at '0', and followed by bit *59A at '0'. This sequence 01111110 never appears elsewhere in bit A, so it uniquely identifies the following second 00 minute marker. |
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- *In minutes lengthened or shortened by a positive or negative leap second all these numbers are correspondingly increased or decreased by one (i.e. during these 61- or 59- second minutes the position of the time and date code is shifted by one second relative to the start of that minute). |
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==See also== |
==See also== |
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Revision as of 17:21, 15 November 2006
The National Physical Laboratory time signal is a broadcast from the
kHz, the same frequency used by WWVB
. The signal strength is greater than 10 mV/m at 100 km and greater than 100 μV/m at 1000 km from the transmitter. The signal is widely used in northern and western Europe. The carrier frequency is maintained at 60 kHz to within 2 parts in 1012.
The transmitter’s
callsign is MSF. It is not an abbreviation: ‘M’ is one of the prefixes allocated to the United Kingdom, and the letters 'SF' were randomly allocated. However, Post Office
staff that operated the station in 1951 insist that the name derives from the Modulated Standard Frequency scientific reference transmissions started in that year.
Early in 2007 the NPL will start new time signal transmissions from the
kHz
. The formal inauguration of the relocated facility will be 1 April 2007, when the name of the service will change to "The time from NPL" and the signal from Rugby will be switched off.
There will be a series of tests in the run up to the changeover, information on these is available from the
National Physical Laboratory
.
Protocol
The MSF time and date code format is summarised in the diagrams above. Simple on-off carrier modulation is used, the rise and fall times of the carrier are determined by the combination of antenna and transmitter. The timing of these edges is governed by the seconds and minutes of Coordinated Universal Time (UTC), which is always within a second of Greenwich Mean Time (GMT). Every UTC second is marked by an 'off' preceded by at least 500 ms of carrier, and this second marker is transmitted with an accuracy better than ±1 ms.
The first second of the minute begins with a period of 500 ms with the carrier off, to serve as a
seconds
of the minute always begin with at least 100 ms 'off' and end with at least 700 ms of carrier. Seconds 01-16 carry information for the current minute about the difference (DUT1) between atomic and astronomical time, and the remaining seconds convey the time and date code. The time and date code information is always given in terms of UK clock time and date, which is UTC in winter and UTC+1h when Summer Time is in effect, and it relates to the minute following that in which it is transmitted.
Bits 17B-*51B inclusive, and bits 01A-*16A inclusive, are currently set to '0', but may be used in the future. Bits *52B and *59B are currently set at '0' but they may be used in the future.
Minute Identifier Bits *53A, *54A, *55A, *56A, *57A and *58A are all set permanently at '1', and are always preceded by bit *52A at '0', and followed by bit *59A at '0'. This sequence 01111110 never appears elsewhere in bit A, so it uniquely identifies the following second 00 minute marker.
- *In minutes lengthened or shortened by a positive or negative leap second all these numbers are correspondingly increased or decreased by one (i.e. during these 61- or 59- second minutes the position of the time and date code is shifted by one second relative to the start of that minute).