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John Logie Baird's first successful demonstration of real television, that is, being able to reproduce moving images in continuous tones with reflected light, that he performed in October 1925 overcame the sluggishness of both the photocell pickup and amplifier system with a combination of techniques that comprised optically chopping the light to the photocell and using differential amplification to provide video peaking in the amplifier. The differential amplification "squared up" the sides of the pulse amplitude modulated pulses. See his British Patent 270,222, filed 21 October 1925 for details. See the details of his optical chopper system in British Patent 235,619, filed 12 March 1924. These patents are in the "Patents and Articles" section of the forum.AncientBrit wrote:Lack of low frequency response in NBTV signals causes quite a few problems.
This is particularly noticeable if an image comprises say broad vertical black and white bars.
The lack of direct coupling means that the waveform ends up with a pronounced tilt at the these locations.
Lack of low frequency response in NBTV signals causes quite a few problems.
This is particularly noticeable if an image comprises say broad vertical black and white bars.
The lack of direct coupling means that the waveform ends up with a pronounced tilt at the these locations.
An alternative method of recording NBTV to video tape (as opposed to audio tape) is to up-convert the signal to 625/50 (or 525/60) and record directly to VCR.
I suspect that once he had photocells with better response time, the extra complexity of the optical chopper wheel and its associated drive was not worth the small increase in picture quality.DrZarkov wrote:As you can see on old pictures of Mr. Bairds devices, he used it in the beginning, but later it seems that he has abandoned this idea. I wonder why?
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