Since 1932, Rene BARTHELEMY searching for a better image quality, experimented in his laboratory of the Compagnie des Compteurs de Montrouge, the analysis and synthesis of the image in 60 lines of definition.
He uses then a 60 holes Nipkow disc rotating at 1500rpm speed.
One of the main obstacles BARTHELEMY and his team faced by then, was the important loss of light through the scanning disc, which got very small holes (1/3rd diameter). The televised scene must be so very strongly enlightened to allow sufficient amount of light to sensitize the single photocell placed behind the disc.
Characteristics of the prototype
However, television progressed quickly and in April 1935, BARTHELEMY and his team are able to provide the equipment necessary to the french Administration of the Postal and Telecommunications (P.T.T.)authorities to carry out the first official Television broadcasting in 60 lines.
- This machine is inspired, with regard to its external appearance, from the 30 lines mechanical television set built by the german Co. TEKADE in 1932.
- The box reflects the art déco style of those times, but the similarity with the TEKADE set ends here.
- The prototype is equipped with a 60 holes Nipkow disc with each 3/10rd millimetre in diameter. This provide thus, an image definition of 60 lines. A synchronous motor, controlled by the frequency of the electric sector, drive the scanning disc at 1500 rpm speed; It ensures a very good stability for a frame rate of 25 per second with no flickering.
- The format of the image is 4/3, allowing the visualization of films and its real dimension is 20 millimeters width by on 18 millimetres high.
- A strong magnifying lens must be used to bring a minimum of comfort of observation.
- For a definition of 60 lines, it is very difficult to use a neon lamp behind a Nipkow disc, due to the important loss of light passing through the tiny holes. That is why a leds array has been used in place of it on this machine. So, the leds gives good bright images (25 X 10.000 mcd). In 1935, these components doesn't exist, that's why, for the first official emission of television done in 60 lines and conducted by the postal and telecommunications authorities, the reception was obtained on aparatus equiped with cathodic ray tube.
- The tubes video amplifier has been recently replaced by a modern ci-based circuit, giving better performances and unexpected good images for this defintion. By then, the machine's weight has been reduced by 10 kilos (!).