GB693897A - Improvements in systems for synchronizing pictures in television - Google Patents

Abstract

693,897. Television. RADIO INDUSTRIE. Nov. 14, 1949 [Nov. 16, 1948], No. 29096/49 Class 40 (iii). In a television synchronizing system, the line signals 4 (Fig. 2), are transmitted as normal amplitude modulations of the carrier and the frame synchronizing signal 6 is transmitted by momentarily shifting the frequency of an oscillation 13, lying within the video frequency range, which is applied to modulate the transmitted carrier-wave during the frame blanking interval 5. The oscillation is chosen so that at least three complete cycles can be accommodated in the time period of a line synchronizing signal, a frequency of 5.0 Mc. being suggested for an 800 line system. The frequency shift may be of the order of 0.5 Mc. either as an increase or a decrease. Alternatively the frequency may successively undergo two variations in opposite directions. The apparatus at the transmitter (Fig. 3) comprises a first tube 9 to which is applied the oscillation 13 from a source 14, the tube, which is normally cut off, being rendered conducting for the duration of the blanking interval by pulses 5 from a generator 8, and the frequency of the source 14 being changed (decreased as shown) for the duration of the frame signals under the control of further pulses 6 from a generator 7. The anode signals are then applied to a second, normally conducting, tube 17 which is cut off for the duration of line synchronizing signals 4 by pulses from a generator 19 whereby there is finally obtained from the anode the full synchronizing signal as shown in Fig. 2. At the receiver, Fig. 6, the synchronizing signals are first separated from the video signals in a tube 27. A filter 31, 32, 33, 35 adjusted to pass frequencies below 1.5 Mc. then selects the line signals to produce an output at point SL, and a frequency discriminator circuit comprising a transformer 28, 29, 37 tuned to 5 Mc. and diodes 39, 40 selects the oscillation 13 and produces an output pulse at point 46 when the frequency changes. Specifications 682,847 and 683,114 are referred to.