31 July 2020 tbs.pm/70569

A description of the Baird equipment.

From the Nottingham Journal for 3 October 1936

TEST transmissions of television were recommenced this week, and in November the first regular service will be inaugurated.

Everybody knows, of course, that a complete television transmitting equipment has been manufactured by Baird Television, Ltd. and installed at the B.B.C.’s Alexandra Palace Television Station to work in double harness with the equipment of the Marconi–E.M.I. group.

The whole of the apparatus installed by Bairds was designed, built, and tested at the Crystal Palace. This enabled staff abilities to be used to the full in order to ensure that every detail was satisfactory.

The Baird Company has provided two machines to televise talking films together with their sound, a studio installation to transmit announcers or artists in the form of close-ups or three-quarter length pictures, and a new machine which films the studio scene, develops the film practically instantaneously, and sends it out as a television picture thirty seconds after it is taken!

Actually, I am told, before the announcer can walk from the studio into the open air his picture is being broadcast.

The installation is a masterpiece of technical efficiency and engineering ability. According to programme needs, any one of these separate television devices is brought into operation.

Spotlight Studio

Two 240-line telecine scanners for transmitting sound film, as supplied by Baird Television to the B.B.C. for the Alexandra Palace station.

In the “Spotlight Studio” which takes close-ups and three-quarter length “shots,” a steady beam of light from an arc lamp is concentrated into a moving spot of light which traces a line of light over every part of the subject twenty-five times a second, making 240 traces each time!

At this almost incredible speed the point of light ceases to be noticed by the subject and the illumination seems to be nothing more than normal room lighting and causes not the slightest discomfort.

The light reflected from the subject being televised, during the whole time that this spot is tracing its path, is reflected on to a new type of photo-electric cell, which has 3,000 times the sensitivity of any cell previously manufactured.

In this was, the light variations which are picked up are converted into electrical variations. The appropriate sound and the necessary signals which hold the picture steady are also generated at the same time, and after leaving the control room the vision and sound signals go to their respective transmitters.

Fastest Film Developing.

With the remarkable filming equipment referred to scenes in the studio are photographed by means of a specially-designed cinematograph camera, the sound being recorded on the film at the same time.

The film is then passed through photographic processing tanks, where it is developed, fixed and washed.

The film negative, perfect in every detail, is then passed in front of a disc scanning unit so that the individual pictures on the film are spilt up by the scanning holes into an electrical television signal.

At the same time the sound is reproduced from the film sound track, after which the film itself is wound up wet. After drying it can be used again as often as desired, so that events occurring early in the day may be repeated later at convenient times.

The remarkable speeding up in the photographic part of this apparatus has excited enormous interest among photographic experts. It reduces the work of hours to seconds. The operator uses the camera in a manner almost identical to that of a talking film unit, and is able readily to make the required adjustments to suit any type of scene, whether close-ups, medium shots or fully extended views.

Television Talkies

John Logie Baird, photographed in 1936 by Howard Coster for ‘The Bystander’

As to the apparatus which televises the ordinary talking films, two machines are employed so that it is possible to fade from one unit to the other without delay when consecutive reels of film are being televised, just as to done in the public cinema theatres.

In the radio transmitter which is responsible for radiating the television signals an entirely new type of water-cooled valve is employed. The parts of these valves are assembled on the spot, the vacuum being produced by air pumps which form part of the apparatus.

The switch-over from one valve to another can be effected practically instantaneously.

The valve not in use can be taken to pieces and new parts fitted if required, without the necessity of replacing the complete valve. Engineers will appreciate the many advantages of this important development of a demountable valve.

This represents a new departure from past practice, a course adopted by the Baird Company to provide the extreme stability necessary at the enormously high frequencies employed – 45 million cycles per second.

Range of Station

Reliability of service is thereby ensured and it is interesting to note also that the amplifiers throughout the chain of equipment handle signals of frequencies from ten cycles to over two million cycles, without any mutilation.

Although it has been widely stated that the range of this installation will be limited to some twenty-five to thirty miles, I am told that it is too early to give any definite figures, particularly as television apparatus of this power and efficiency has never hitherto been used in service conditions.

It is believed that the range quoted is a very conservative figure, and it would not be surprising if, in a few weeks’ time, picture reception is found to be available well outside this area.

In the control room the producers, watching the television receivers, can make instantaneous changes to any transmission as required.

The form of the radiated television signal is maintained to a definite standard, which ensures the automatic operation of all television receivers tuned to the signal, wherever they are situated.

Consequently the receiver is completely controlled by the transmitter.

Quality

Broadcast sound, as we now know it, has very obvious limitations from the point of view of quality, owing to the crowded conditions of the ether.

With the sound accompanying the television transmission, however, these restrictions are swept away.

The whole gamut of frequencies which together give the transients and overtones inseparable from quality sound, can be included in the broadcast television sound.

Every effort has been made to ensure absolute reliability of service and at every stage in the process quantitative and qualitative checks are made to ensure that the final radiated picture for reception in the home is satisfactory in every detail.

In the picture check units, the latest form of “Cathoviser” cathode ray tube developed by Baird Television Ltd. has been used. These give a brilliant black and white picture almost a foot square [30cm²].

These cathode ray tubes represent the most modern television practice, and for size, colour and brilliance are said to be unequalled. They are estimated to have a life of several years of normal “looking in.”

Russ J Graham writes: There’s no getting away from it: mechanical television was cumbersome, and Baird’s various tweaks to make it more competitive with the all-electronic systems that were available could only make that worse.

The film step, the only way of getting a mechanical system up as high as 240-lines (the all-electronic system had already reached 405-lines [actually 337, but that’s another story]; it would reach France next year at 455-lines and Nazi Germany would have a working 1,000-line wired system by 1940) took a massive amount of space, toiling technical operatives to babysit it and had a continual potential problem of what could happen if the film snapped – the downtime for the entire television service could be hours.

Add to that the scanning spot-beam, which was severely limiting as to what could be televised, didn’t work for outside broadcasts, and, despite what Mr Stephens says, was noticed by those put in front of it thanks to the blinding headaches it could cause, and you’ve got a dud on your hands.

Plus mechanical television sets, whilst easier for the home enthusiast to build than all-electronic ones, were more expensive; manufacturers of complete sets were already producing all-electronic models that could cope with both 405- and 240-lines, rendering the difference moot to most people and showing viewers that 405 interlaced lines were superior to 240 non-interlaced and actually showed more detail.

It is no surprise that the BBC gave up on it within 4 months.