GB558578A - Synchronizing generators - Google Patents

Abstract

558,578. Testing television apparatus. STANDARD TELEPHONES & CABLES, Ltd. Jan. 8, 1943, No. 379. Convention date, Jan. 14, 1942. [Class 40 (iii)] A synchronizing generator for testing television apparatus comprising means for generating line and frame scanning signals, means for adjusting the frequency of the said signals, and means for adding to said signals uniformly timed pulses serving to test the scanning linearity of the television apparatus. In the arrangement shown in Fig. 3, a master generator 20 generates a 31.5 kc. sine wave and feeds it to a master oscillator 24 producing pulses of the same frequency. These master pulses are fed to a second oscillator 25 producing pulses at half the frequency, namely at 15,750 per second for line scanning. The master pulses are also fed to a chain of frequency dividers 30 ... 33 which divide the frequency successively by 7, 5, 5 and 3 yielding ultimately pulses at 60 per second. These pulses are fed back to an interlocking circuit 22, which is connected to a main A.C. supply at 60 cycles per second and serves to operate a circuit 21 to stabilize the frequency of the master generator 20, for example as described in Specification 554,588. The oscillators 24, 25 and the dividers 30 ... 33 may be relaxation oscillators of the kind shown in Fig. 1, the several switches 8 serving to adjust the frequencies being all mechanically ganged together. Outputs from the circuits of Fig. 3 are supplied to a mixing chain of circuits, Fig. 4. The line frequency pulses from the generator 25 are fed to a carrier wave generator 41 and to a shaping device 42. The carrier wave from generator 41 is fed to a keying circuit 44 controlling a mixer 47 between the shaping devices 42, 53. The keying circuit 44 is controlled by the pulses at 60 cycles per second from the last divider 33. In addition to these parts, which resemble the arrangement of Fig. 3 of Specification 542,258, the carrier wave output from generator 41 may be applied to the mixer 47 through resistance 49 and switch 48, and the output from the divider 31 may also be fed to the mixer through lead 54 and switch 52. If the output of the final shaping device 53 is fed to a television cathode-ray tube, the pattern indicated by Fig. 5 is produced. The pulses due to the connections between generator 41 and mixer 47 through switch 48 produce the striations 59, 60 ; and the pulses from the divider 31, which includes harmonics of the fundamental, produce the alternate scale-like markings 65, 66. The correctness of these striations and markings indicate correct linearity of the scanning circuits.