Tektronix SPG8000 Technical Reference page 17

System timing
GPS RCVR. Option GPS is required to use the GPS Receiver feature. The GPS
signal can be selected as the source for a time of day clock used for timecode
outputs, and as a phase reference for video outputs. The GPS signal carries the
time represented as the number of weeks and number of seconds since the GPS
Epoch (0:00:00 UTC, January 6 1980). For example, 12:00:00 UTC on November
5, 2008 is represented as 1504 weeks plus 302,400 seconds. An additional 14 leap
seconds that have passed between January 1980 and November 2008 are also
signalled in messages from the GPS satellite system.
Internal Time Set *. Option GPS is required for the GPS/NTP portion of the
Internal Time Set feature. If you want to set Time Setup to internal mode, enter the
current date and time and then set the Time Setup to Internal in order to transfer
that time to the Master Time. The time zone offset and leap second information is
used to convert local time to a master time that is equivalent to GPS time. This
allows the Epoch and NTP processes to work the same for both internal and GPS
time modes. Set the local time zone offset before setting the internal time.
VITC Reader. When the SPG8000 is genlocked to NTSC or PAL, the Vertical
Interval Timecode on the genlock reference input can be decoded and used as the
time source. This time can be viewed on the status bar, and is used as the time
source for all the time code outputs. Since the phase of the video signals are set by
the genlock, the epoch system does not operate from the VITC input.
LTC Reader. When the reference source is set to INTERNAL, NTSC, PAL or
HD SYNC, the LTC signal applied to the LTC 1 input can be used at the time
source. This time can be viewed on the status bar and is used as a time source for
all the time code outputs. Since the LTC reader does not provide date and time
information, the epoch system does not operate from the LTC input.
Time Setup Selection. Option GPS is required to use GPS as the reference source.
The possible Time code sources depend on the selected Reference source. If GPS
signal is the selected reference source, then GPS or internal time is available. If
Genlock is the selected reference source, then VITC or internal time is available. If
Internal is the selected reference source, then internal time is the time code source.
If VITC is the time code source, then the time synchronization Mode needs to be
set. There are three choices. Synchronize now sets the time when the user presses
the ENTER button (if the incoming time is valid and stable). Synchronize once
sets the time once when a valid and stable time code is detected. Follow sets the
time every time a new stable and valid time is detected.
Master Time. The Master Time is the basis for all timecode outputs and for the
phase reference of all video outputs.
Leap Seconds. Leap second information is stored and then updated by satellite
every 20 to 30 minutes.
SPG8000 Technical Reference 5