Tektronix TG700, Руководство пользователя

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GPS7 GPS Synchronization and Timecode Module
GPS RCVR.
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 *.
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 SNTP 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 GPS7 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.
Time Setup Selection. 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
Offset to TAI. TAI is the International Atomic Time, represented as the number of
seconds since the epoch of 0:00:00 January 1, 1958. Proposed standard SMPTE
404M de
fi nes the SMPTE Epoch at that same moment. There are exactly 8040
days and 19 leap seconds between the SMPTE Epoch (TAI) and the GPS Epoch.
Epoch Calculations.
The number of seconds since the SMPTE Epoch is used
to precisely align video frames with the Master Time clock. For example, an
NTSC system operates at 29.97 frames per second (30 fps/1.001), so there are
precisely 30,000 frames every 1001 seconds. By knowing the total number of
seconds since the SMPTE Epoch, when all video frames were perfectly aligned,
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