Model 5601MSC
Model 5601MSC Master SPG/Master Clock System
OPERATION Revision 2.2 Page - 39
2.3.2. Coordinated Universal Time (UTC)
Coordinated Universal Time (UTC) is used worldwide as the basis of civil time and runs at the same
rate as International Atomic Time (TAI). Unlike atomic time, Coordinated Universal Time is kept within
one second of mean solar time, or Greenwich Mean Time (GMT). The rotation of the earth is very
slightly slowing which causes the solar day to lengthen by a fraction of a second. This introduces a
slight error between atomic time and solar time. Over weeks, months, and years, the error can add up
until atomic time is a full second ahead of solar time. Because UTC runs at the same rate as atomic
time, it must be slowed down if it is to match solar time.
Leap seconds are introduced periodically and cause UTC clocks to count one extra second in a day to
slow them down. The rotation of the earth is unpredictable which means the need for a leap second
cannot be predicted more than six months in advance. If a leap second is necessary, it will occur at the
end of the day usually on either June 30
th
, or December 31
st
. Refer to www.iers.org for more information
and bulletins on upcoming leap seconds. Leap seconds can cause complications with 25Hz LTC or
PAL VITC. See the timecode note in section 2.3.4.2.3 for more information.
The 5601MSC expects that the time reference provides UTC time. This is a requirement for the NTP
server or modem hosting using the NRC protocol. When either of these options are utilized, the time
reference source must provide UTC time.
2.3.3. Time Reference Sources
The system clock can be referenced in one of several ways. The reference type is selected in the
Time menu located in the INPUT root menu. The Reference Src menu item is used to select between
GPS, Modem, Syncro, LTC, VITC, IRIG, SNTP and None. See sections 2.3.3.1 to 2.3.3.8 for detailed
descriptions of each time reference type. Note that the time reference will be forced to GPS if the
frequency reference has been set to GPS, no matter what has been selected here.
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