Museum of the Broadcast Television Camera

1934 RCA experimental Sync Pulse Generator

1934 RCA experimental Sync Pulse Generator

This 1933-34 Mechanical SPG used a motor driven disk which rotated at 1440 RPM. Two rows of slits illuminated two photocells that produced sync pulses and blanking signals. Different line and frame rates could be produced by changing the disk and motor speed.
Experiments were carried out with different line and frame rates were carried out and compared with 16mm film. The frame rates was 24 frames/sec:-
60 lines.......entirley inadequate
120 lines ....hardly passable
180 lines.....minimum acceptable
240 lines.....satisfactory
360 lines.....excellent
480 lines.....equivalent for practical conditions.

During these tests flicker and hum were problems as the mains frequency was 60c/s Increasing the frame rate to 30 frames/sec reduced the hum problems but the flicker was still unacceptable. The frame rate needed to be at least 48 to minimise the flicker. A practical solution to the problem was Interlaced scanning which gave a picture repetition rate of 60 per sec and as the mains frequency was 60c/s the hum, if present, was stationary.

Kell, Bedford & Trainer report that at higher line speeds the mechanical Sync Pulse Generator's accuracy of construction led to difficulties and an electronic generator has been developed.

 

Ref. Maloff : Cathode Ray Tube in television reception, RCA c. 1933
Ref: Kell, Bedford and Trainer : Scanning Sequences, RCA

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