Technical data

Installation & Operation Manual GM-TTT
Page 68
5.7 Real Time Coupling of Time Code and Video
The safest method to generate a real time coupled time code which is in sync with the video
signal is to synchronise the video sync generator (SPG) to real time. Some DCF77 or GPS
systems offer a stable 10MHz output, and some SPG's may also be coupled by using these
10MHz. Furthermore, a stable seconds pulse is used, which is output from the DCF77 or GPS
receiver. A wiring option is shown in the chapter entitled “System Overview“.
If this system shall only be locally operated, no special alignment of the systems will be
required:
• In the SET - ... - LOCK menu of the GM-TTT, select genlock = bb and confirm with enter.
Press the genlock button.
• Switch the SPG to 10MHz genlock. Does the system accept this reference?
• At the GM-TTT the difference between the seconds pulse and the V1 pulse can be
measured: in the TEST - 3 menu. Is this value stable?
During power-on and after every change of the synchronisation mode, the GM-TTT measures
the phase relationship of the sync pulse compared to the seconds pulse during about 15
seconds (intern button, genlock button). Then an optimum time is selected for the transfer of
real time into the LTC, to avoid any frame jumps during normal operation. The phase relation-
ship of the sync pulse compared to the seconds pulse may be any within ± 20 ms (the 10MHz
coupling frequency only avoids any drift of the signals), therefore the LTC may constantly differ
from the real time by up to one frame - or four frames when colour lock is used. As an
optimum adjustment is only provided, if all used equipment is in a stable operating condition,
the automatic alignment should be checked for safety reasons (e.g. after a power failure).
Especially a GPS or DCF77 receiver requires more time to achieve stable output frequencies.
This condition is checked in the STATUS - ... - 8 menu: optimally, NOBYCMP indicates 0 or 9,
critical values are 4 or 5. The more the value differs from 4 (in the range of 0 ... 9), the better.
A correction may be performed by reactivating the video synchronisation, i.e. press the intern
button, then the genlock button.
However, if frame 0 of the LTC shall absolutely coincide with the seconds pulse, the sync
generator must be aligned to the seconds pulse, because the LTC is of course generated in
sync with the video signal:
• At the sync generator, the phase of the signal has to be shifted (vertically, horizontally, µ-
seconds) so that the GM-TTT displays the difference 0 in the TEST - ... - 3 menu (the first
seven digits of the display). If colour framing is used in the 625/50 TV system: with V4-
lock the 8
th
position must display 1, with V8-lock it must be 3. Important: After this setting
has been made, the video synchronisation must be reselected, i.e. press the intern button,
followed by the genlock button. Please note: This setting will be lost when the sync
generator is powered off and has to be made again after power-on.