Patent GB-1235039-A (GB)
Title: A method of automatically synchronising a remote television station with a central station
Inventor: LEGLER ERNST
IPC: H04N9/475
Filed: 1969-10-09
Abstract: 1,235,039. Synchronizing television signals. FERNSEH G.m.b.H. 9 Oct., 1969 [9 Oct., 1968], No. 49705/69. Heading H3A. In a method of automatically synchronizing a remote television station with a central station in an interlaced system, which overcomes the delays occurring in the means interconnecting the two stations a frequency and phase comparison is effected between the line sync. pulses at the central station and those transmitted from the remote to the central station and an error signal dependent upon the frequency or phase difference is transmitted from the central to the remote station at which it regulates the frequency and phase of the line sync. pulses so as to coincide with those at the central station. In addition, from the vertical sync. pulses contained in the sync. signal of the signal transmitted from the remote to the central station, a second series of comparison pulses is derived their duration being less than one half the line duration, and from one comparison pulse series at least one auxiliary pulse series with the same sequence frequency and duration is derived, but having a predetermined time delay relative to the pulse series it is derived from. A comparison is effected in a coincidence circuit between the comparison pulse series from the central station and the auxiliary pulse series, the coincidence circuit delivering a YES/NO signal which is transmitted to the remote station, and in the case of non-coincidence maintains the relationship between the line and vertical frequencies at the remote station at a prescribed value different from the nominal value for such time until coincidence is established. The YES signal is then transmitted to the remote station and restores the ratio between the vertical and line frequencies to the nominal value, and the auxiliary pulse series is disconnected, synchronism being established between the synchronizing signal in the central station and that in the signals transmitted to the central station from the remote station. In an embodiment comprising a PAL colour transmission system, the central and remote stations comprise pulse generators 1, 9 respectively, Fig. 1, feeding line (H), vertical (V), blanking (A) and synchronizing (S) signals to respective scanners and coders 4, 10. The synchronizing signals (S) are additionally fed to code recognition pulse generators 5, 11 respectively, which supply recognition (K) and PAL recognition (P) pulses to the scanners and coders 4, 10 respectively. The scanners and coders 4, 10 deliver four separate colour signals (FBAS) to control apparatus 6, 12 respectively: the central control apparatus 6 feeds at 7 a studio output, while the remote control apparatus 12 feeds via a wide-band path 8 into the central station control apparatus 6. The pulse generator 1 at the central station is driven via PAL coupler 4 from colour carrier generator 3, which also supplies an output (F) to the scanner and coder 4. The pulse generator 9 at the remote station is driven from generator 24, operating at twice line frequency, a local colour carrier generator 29 supplying an output (F) to scanner and coder 10. The central station also contains apparatus 13 for synchronizing the remote station, to which the sync. signal (S) is applied from pulse generator 1 and also the incoming signals from the remote station. Apparatus 13 produces a line control signal U H  and vertical control signal U v  which are applied to a modulator 21 for transmission on two separate carrier frequencies to the remote station, via narrow-band path 22. In the remote station these signals are demodulated by demodulator 23 and applied to control the generator 24. Apparatus for synchronizing the remote station (13, Fig. 1).-A circuit 31, Fig. 3, separates out the sync. pulses in the signals from the remote station, and from these vertical frequency comparison pulses (V N ) are separated out by the circuit 32. The comparison pulses are delayed e.g. one line period in a delay network 33, and undelayed (V N ) and delayed (V N1 ) pulses are combined in an adding circuit 34. The combined pulses are applied to a coincidence stage 35, the second input of which comprises vertical synchronizing pulses (V z ) derived from the synchronizing signals (S z ) at the central station by means of circuit 36. Coincidence stage 35 delivers a YES signal if there is coincidence between a pulse of the series V z  with a pulse of the delayed auxiliary pulse series V N1 ; otherwise, a NO signal is delivered. Synchronizing apparatus at the remote station, -The generator (24, Fig. 1) comprises an oscillator 42, Fig. 4, operating at double line frequency, its frequency being controlled by the signal U H  from the central station. From the output of oscillator 42 line frequency signals are produced by means of a times two divider 43: its output is also fed to a counter 41, to which is coupled the control signal U v  from the central station. If signal U v  comprises a YES signal the counter 41 delivers an output pulse with the vertical frequency 50 Hz., after each 625 oscillations at line frequency: if, however, the signal is NO the output pulse is delivered after 627 oscillations at line frequency. The vertical frequency is therefore smaller than its nominal value, and each frame increased by one line: the introduction of the vertical frequency comparison pulses with reduced frequency as compared with the comparison pulses of the central station therefore takes place in such a direction that the former occur one frame earlier than the corresponding pulses of the original comparison pulse series from which they are derived. On coincidence of a delayed pulse and a pulse from the central station the signal U v  switches the counter back from 627 to 625 so that the next comparison pulse of the remote station reaches the central station at the correct time to maintain synchronism. The signal U v  at the same time opens switch 37, Fig. 3, disconnecting the delayed pulses V N1 . The Specification also describes a modified arrangement (Figs. 5, 6, not shown) shortening the time required for synchronism: in this " running through " of the vertical comparison pulses can occur in either direction, the direction being chosen which will bring the pulses more quickly into synchronism with the pulses of the comparison series of the central station.