Synopsis: J.L.Baird had little day to day contact with Baird Television Ltd. (BTL) from 1933 onwards. This company, which later became Cinema Television Ltd., provided much equipment and undertook research for the radar programme in Britain before and during WWII.
The Metropolitan-Vickers demountable tetrode valve
The Chain Home radar defence system which was built around the coast of Britain from 1937 to 1940 needed powerful transmitter valves. Some of the valves used for this system were Metropolitan-Vickers constantly evacuated demountable tetrodes type 431B.i There is some evidence to suggest that Baird Television Limited may have assisted in the development of the circuitry for these valves. Douglas Brown has written that E.G. Bowen working on radar development, used "...the linear output stages of Baird's T.V. transmitter from the [Alexandra] Palace", for Watson-Watt's first attempts at detecting aircraft with radar from 31 August to 11 September 1936.ii Since writing this letter Brown has stated that the first tetrode valved transmitter used by BTL was installed at the Crystal Palace for use in their 180-line tests.iii According to civilian scientist Mr N. Hecht, who was responsible for reporting BTL television reconnaissance activities to the Air Ministry, the company was in April of 1936, "…building a new transmitter with a power of 500 k.w. using Metrovick demountable valves".iv This transmitter was most probably related to one constructed in 1931 for use on a wavelength of 2,500 metres for the Post Office Radio Station at Rugby.v
Ray Herbert's article in Transmission Lines quotes a personal letter from Donald Priest who was involved in Watson Watt's radar experiments. Priest says, "It is almost certain that the design of these transmitters was done by the same people who designed the Baird transmitter you mentioned. There were not many people around who knew how to do such things." In the same article he notes "Undoubtedly the 24 months of development work by the Baird Company must have had a significant influence on the CH radar transmitter design".vi
Baird Television Ltd, the Rapid Processing Camera Projector and Bawdsey Manor
In early 1940 Baird Television Ltd provided equipment for the Radar Photographic Display System 1498. The supply of this equipment was a result of a series of investigations.
The BTL equipment was derived from their Intermediate Film system that they used for broadcast television as well as aerial reconnaissance. BTL along with Marconi-EMI were chosen for a trial at Alexandra Palace to select a public television system. The trial started on the first of November 1936 but by early 1937 the Marconi-EMI equipment was chosen. One of the reasons cited for the failure of BTL was its use of the Intermediate Film system. This apparatus recorded programmes with a cine camera, then processed the film in 50 seconds and immediately electronically scanned the wet film for 'near-live' television. Intermediate Film was much maligned for being cumbersome and leaking noxious chemicals. However, the day the BTL broadcasts were switched off, 5th of February 1937, the Admiralty visited BTL requesting the Intermediate Film system be adapted for signalling.vii There then followed a series of communications between the Admiralty, Air Ministry, Royal Signals and BTL concerning a television based signalling systems. Various apparatus were designed and in May 1938 some equipment was demonstrated to the Admiralty.viii
When the Telecommunications Research Establishment at Bawdsey Manor required equipment for photographing radar traces they were therefore aware of suitable equipment available from Baird Television Ltd. This information is recorded in Public Record Office (PRO) File AIR 2/2877 entitled "Report and drawings on rapid processing camera projector, Baird Television Ltd". The file was opened in November 1938 to address the "Mitigation of jamming by means other than wavelength change". The project was given an 'A+' priority rating and included four methods of investigation.
a) Special screen characteristics used in conjunction with a stroboscope and filters.
b) Photographic methods.
c) Receiver methods.
d) Spaced aerial systems which aim at laying a zero on to a jamming aircraft.
It was assumed that frequency change would counter constant wave jamming but other methods were required to counter "…jamming signals consisting of discreet waveforms, e.g. spark". Photography of radar Cathode Ray Tubes (CRT) had already proved useful and this method was investigated. A. P. Rowe, Superintendent of Bawdsey Manorix thought that the BTL system could accomplish such a task and requested further information. After consultation the company offered to build a completely new system in four weeks rather than modify their existing equipment which would take longer.
Bawdsey were prepared to pay one thousand pounds for a non-secret contract for the necessary development as one system was "…urgently needed for anti-jamming". Initially the camera was described as having the following attributes
1) Capacity of 400ft (122 metre) film magazine providing for 5 hours use and associated chemicals in stainless steel tanks.
2) Intermittent gear advancing film Ľ" (0.6 cm) per second, each exposure measuring 1"x Ľ" (2.5 x 0.6cm)
3) Dallmeyer 2" (5cm) f1.9 Super Six anastigmatic lens for camera and 6" (15 cm) f2.9 lens for projection which provided an 8 X magnification and was illuminated by a 250 Watt bulb.
The lamp was arranged to illuminate the film passing over a glass covered aperture in the base of the fixing tank and 10 projected images could be viewed simultaneously.
In February 1940 BTL offered an improved system. By this time initial apprehension regarding speed of film development had been overcome and total exposure to projection had been reduced to ten seconds. BTL suggested further modifications such as continuously fed rather than intermittent film progression as well as reducing the length of film between exposure and projection gates. By means of these modifications it was possible to reduce the processing time still further to just six seconds. Advancement of this part of the process was aided by parallel investigations by BTL into recording on to paper as an alternative to film as part of their facsimile investigations. This system was later also incorporated into a ballistics contract which amongst other things helped to develop the explosive for the Grandslam bomb used so successfully for destroying U-boat pens.x
Whether the technologies developed by Baird Television Ltd for Bawdsey Manor were ever operationally used is not recorded in the PRO file AIR 2/2877 However, fortunately Richard H.G. Martin has been able to complete the history of this investigation. Martin has published an article entitled ‘Radar Photographic Display System 1498' for Transmission Lines and I quote from this article for the final word on this subject.
The origins of the RPDS may be traced back to the first use of radar photography, for operational purposes, at the CHL station at Walton-on the-Naze in February/March 1940. At the time, enemy aircraft, under cover of darkness, were causing problems by laying mines in the approaches to the Thames Estuary. An experimental Baird camera, with integral processor and forming part of the Company’s development of television displays, was used to photograph the amplitude modulated trace (together with time and bearing information). The film could be immediately processed and be ready for collection by the Admiralty the following morning for assistance in mine sweeping operations.xi
Development and production of cathode ray tubes
As a result of war being declared in September 1939 Baird Television Ltd was placed into receivership. Television technicians had skills useful to the radar programme and some staff had already left to work on radar development. In October 1939 William Sholto Douglas suggested that BTL could be utilised for "…production of RDF equipment [Radio Direction Finding = radar]".xii Rather than close down BTL cathode ray tube (CRT) production facilities at Crystal Palace it was decided re-organise the company using one of its subsidiaries. By May 1940 BTL was called Cinema Television Ltd. Starting with just forty staff and one factory, by December 1944 the company had expanded to 1,000 staff in three factories. 95% of the employees were engaged on the production of equipment for the Services, whilst only 5% on its development. Among military equipment produced during the war were Special Radio Receivers, Unexploded Bomb Detection Equipment, Photoelectric Cells as well as 30,000 Mine Detectors.xiii
However, the greatest manufacturing effort by Cinema Television Ltd was cathode ray tubes for the radar programme. The company was represented by T.M.C.Lance at the Committee for the Co-ordination of Cathode Ray Tube Development. EMI, Cossor, Mullard, Ferranti and Cosmos were also members of the committee. The minutes of these meetings are recorded in PRO files AVIA 7/1231 and AVIA 7/1232.
Manufacture of CRTs by Cinema Television Ltd began in January of 1942 in their Rotunda building on the Crystal Palace site and later at a new factory in Worsley Bridge Road a couple of miles away. The company produced various types including VCR 139A, VCR 140, VCR 516, VCR 522 and VCR 97 among others. Special tubes were developed to help in the location of the launching sites of V1 Flying Bombs.xiv CTL also developed and produced the dark trace tubes known as Skiatrons or VCR 520 to the Air Ministry and NCR 17 to the Admiralty. As early as 1941 CTL vacuum physicist Bob Bartle obtained patent GB 614 261 for modifications to Skiatrons. Production Skiatrons varied in size from nine inches to two inches (23 to 5cm) screen diameter and were used for a variety of applications. The smallest Skiatron tube was developed for a special contract. The total amount of Skiatron production was approximately 15,000. According to company Director, Captain A.G.D.West, by June 1945 Cinema Television Ltd had produced an impressive total of 110,000 Cathode ray tubes of all types for the war effort.
