03-11-2016, 09:01 PM
The original 405 line system had 385 active lines. Interestingly, the 441 line system in use in France until 1956 had the same number of active lines, the frame blanking period occupied many more lines than our 405 line system.
Unlike the 405 line system where the frame blanking period started at the commencement of the eight broad frame pulse chain, in the 441 line system six lines were blanked out before the start of the frame broad pulses. Both systems had eight broad frame pulses. With 405 lines max video bandwidth need only be 2.7Mhz, max 3Mhz, whereas in the 441 line system max video bandwidth has to be almost 3.5Mhz.
From the "Black Book" The 1939 frame divider chain was designed to replace earlier apparatus. The new circuit employed three blocking oscillators which functioned as two divide by nine and one divide by five counters. Valves used for each counter were a D63 double diode and a KTZ63 pentode. The 20,250Hz pulse chain from the master oscillator was supplied to the first blocking oscillator, nine pulses were counted and the output pulse supplied to next divide by nine blocking oscillator. The divide by 81 signal is finally supplied to the divide by five oscillator. The output from the divider chain is amplified by a great big N34 pentode. This is the trigger pulse to initiate the start of the eight broad pulse chain.
The American 343 system did indeed have a line frequency which was close to 405 lines. 10290 for 343/60. 10125 for 405/50.
343 = 7 X 7 X 7.
Geordie McBoyne.
Unlike the 405 line system where the frame blanking period started at the commencement of the eight broad frame pulse chain, in the 441 line system six lines were blanked out before the start of the frame broad pulses. Both systems had eight broad frame pulses. With 405 lines max video bandwidth need only be 2.7Mhz, max 3Mhz, whereas in the 441 line system max video bandwidth has to be almost 3.5Mhz.
From the "Black Book" The 1939 frame divider chain was designed to replace earlier apparatus. The new circuit employed three blocking oscillators which functioned as two divide by nine and one divide by five counters. Valves used for each counter were a D63 double diode and a KTZ63 pentode. The 20,250Hz pulse chain from the master oscillator was supplied to the first blocking oscillator, nine pulses were counted and the output pulse supplied to next divide by nine blocking oscillator. The divide by 81 signal is finally supplied to the divide by five oscillator. The output from the divider chain is amplified by a great big N34 pentode. This is the trigger pulse to initiate the start of the eight broad pulse chain.
The American 343 system did indeed have a line frequency which was close to 405 lines. 10290 for 343/60. 10125 for 405/50.
343 = 7 X 7 X 7.
Geordie McBoyne.
