The 180 line cathodic prototypes

History

At the beginning of 1935, the Minister for the french PTT, Georges MANDEL, presses the Compagnie des Compteurs de Montrouge (C.D.C)to carry out a system of high definition television system (according to the criteria of those times!) and thus, to compete with Germany in this area.

In January of this same year, only the 60 lines is available and it is this definition which will be adopted to carry out the first official emission of Television on April 24, 1935 (see the heading 'History' on this site). However, that does not satisfy Mr. MANDEL. So, Rene BARTHELEMY and his team increased redouble their efforts to get the 180 lines ready as soon as possible. This goal is achieved by end 1935.

On December 8, 1935 takes place the official unveiling of the 180 lines. The reception of the images is done on cathode ray tubes, because the receiving Nipkow disc is completely unusable with this definition. Effectively, the loss of light, already appreciable with the 60 lines, is from now on incompatible with any mechanical observation for the 180 lines, due to the smallness of the holes (lower than 3/10e of millimetre) of the receiving disc.

Does that means that mechanical television disappeared in France with the advent of the 180 lines? Not yet, since the analysis of the image in the studio is still done mechanically!

Indeed, Rene BARTHELEMY had to conceive a wonder of mechanical precision with this Nipkow disc camera featuring 180 tiny holes distributed on three spirals and a motor driving it a 3000 rpm!

The camera did the job, but at what a price to pay!! The single photocell placed behind the disc, required an enormous quantity of light, more than 40.000 luxes, to be able to react to the various variations of luminosity of the scene. The loss of light passing through the Nipkow dics holes, reached more than 90% and the heat dissipated by the numerous projectors inside the studio was such, that a special cooling system had to be studied to bring back the temperature to 25 centigrade degrees.

Hopefully, the photomultiplier tube, invented by the American Philo T. FARNSWORTH in the end 20's, will soon replace the photocell of the 180 lines mechanical camera. Its sensitivity was thousands of times higher than that of the cell. The amount of light necessary to the catch of sight in 180 lines, could be then consioderably reduced.

The 60 and 180 lines TV programs where broadcasted simultaneously until June 1936, moment where the 60 lines was definitively abandonned.

Characteristics of the prototype: