SCIENCE MUSEUM SOUTH KENSINGTON HANDBOOK OF THE COLLECTIONS ILLUSTRATING ELECTRICAL ENGINEERING II. RADIO COMMUNICATION By W. T. O'DEA, B.Sc., A.M.I.E.E. Part I.-History and Development Crown Copyright Reseruea LONDON PUBLISHED BY HIS MAJESTY's STATIONERY OFFICI To be purchued directly from H.M. STATIONERY OFFICI at the following addre:11ea Adutral Houae, Kinpway, London, W.C.z; no, George Street, Edinburgh:& York Street, Manchester 1 ; 1, St, Andrew'• Cretccnr, Cudi.lf So, Chichester Street, Belfa1t or through any Booueller 1934 Price 2s. 6d. net CONTENTS PAGB PREFACE 5 ELECTROMAGNETI<: WAVF13 7 DETECTORS - I I EARLY WIRELESS TELEGRAPHY EXPERIMENTS 17 THE DEVELOPMENT OF WIRELESS TELEGRAPHY - 23 THE THERMIONIC vALVE 38 FuRTHER DEVELOPMENTS IN TRANSMISSION 5 I WIRELESS TELEPHONY REcEIVERS 66 TELEVISION (and Picture Telegraphy) 77 MISCELLANEOUS DEVELOPMENTS (Microphones, Loudspeakers, Measure- ment of Wavelength) 83 REFERENCES - 92 INDEX - 93 LIST OF ILLUSTRATIONS FACING PAGE Fig. I. Brookman's Park twin broadcast transmitters -Frontispiece Fig. 2. Hughes' clockwork transmitter and detector, 1878 8 Fig. 3· Original Hertz Apparatus - Fig. 4· Original Hertz Apparatus - Fig. S· Original Hertz Apparatus - 9 Fig. 6. Oscillators and resonators, 1894- 12 Fig. 7· Lodge coherers, 1889-94 - Fig. 8. Magnetic detectors, 1897, 1902 - Fig. 9· Pedersen tikker, 1901 I3 Fig. IO. Original Fleming diode valves, 1904 - Fig. II. Audion, Lieben-Reisz relay, Pliotron - Fig. IZ. Marconi transmitter and receiver, 1896 Fig. IJ. Lodge-Muirhead and Marconi receivers 17 Fig. 14. Marconi's first tuned transmitter, 1899 Fig. IS. 11 Tune A" coil set, 1900 - 20 Fig. 16. Marconi at Signal Hill, Newfoundland, 1901 Fig. 17. Poldhu aerial, 1901 - 21 Fig. 18. Transformers, condensers, and spark gap, Poldhu, 1901 Fig. 19. Marconi discs for musical spark transmission, 1906-7 22 Fig. 20. Oscillation diagram - 23 Fig. 21. Telefunken spark gap Fig. zz. Duddell high frequency alternator, 1900 26 Fig. 23. Poulsen arc converter Fig. 24· 20o-kW. high frequency alternator set Fig. 25. Jigger for synchronous A.C. set, Carnarvon, 1919 Fig. 26. C.W. disc, Carnarvon, 1919 ---- JO Fig. 27. 48-valve transmitter panel, Carnarvon, 1921 Fig. 28. Original Bellini-Tosi radiogoniometer - JI Fig. 29. Marconi multiple tuned receiver, Fleming diode receiver, and French 8-valve detector-amplifier ----- 32 l FACING PAGB Fig. 30. Transmitter aerials - 33 Fig. 31. Receiving valves 40 Fig. 32. Transmitting valves - - 41 Fig. 33· Catkin receiving valve, 1933 Fig. J4.. Continuously evacuated valve, soo kW. :} so Fig. 35· Short-wave telegraph/telephone transmitter­ - 51 Fig. 36. Rugby single sideband transmitter Fig. 37· Ongar transmitter hall, 1934 :} S+ Fig. 38. Ongar, master oscillator and absorber panel­ 54 Fig. 39· Ongar, amplifier panels 55 Fig. 40. Reflection from the upper atmosphere­ Fig. 41. Marconi ultra short-wave transmitter - ss Fig. 42. Microray transmitting valve and reflector - Fig. 43· Microray receiving reflectors 6o Fig. 44· Writtle broadcast transmitter, 1921 6o Fig. 45· 2LO, London broadcast transmitter, 1923 - Fig. 46. Brookman's Park transmitter hall, 1928 6t Fig. 47· Daventry Empire S.W. broadcasting station, 1932 Fig. 48. 3 early broadcast receivers 61 Fig. 49· "Everyman Four" receiver, 1926 - Fig. so. Marconiphone superheterodyne, 1927 68 Fig. sx. Burndept receiver, 1923 - Fig. 52. Philips all-mains receiver, 1928 69 Fig. 53· Original Baird television transmitter - So Fig. 54· Early loudspeakers - 8t Fig. SS· Moving-coil loudspeakers - Fig. s6. Microphones - =} 86 Fig. 57· Fleming cymometer, 1904 - 8 Fig. 58. Valve maintained tuning forks and piezo-electric crystal - 7 PREFACE HE formation of a Museum of Science was first proposed by the Prince Consort after the Great Exhibition in x8sx, and in 1857 T collections illustrating foods, animal products, examples of structures and building materials, and educational apparatus, were brought together and placed on exhibition in South Kensington. The collections of scientific instruments and apparatus were first formed in 18741 but it was only after 1876 that they became of importance. The Special Loan Collection of Scientific Apparatus which was exhibited in that year in the Museum brought together examples of all kinds from various countries, and a large number of these were acquired for the Museum. Subsequently many additions were made, including in 1884 the collection of machinery formed by the Commissioners of Patents, in I goo the Maudsley Collection of machine tools and marine engine models, and in I 903 the Bennet Woodcraft Collection of engine models and portraits. Until 1899 the Art Collections and the Science and Engineering Collections together formed the South Kensington Museum, but in that year the name was changed to the Victoria and Albert Museum, which included both Collections until 1909, when it was restricted to the Art Collections ; those relating to Science and Technical Industry have since then formed the Science Museum. The aim of the Science Museum, with its Collections and Science Library, is to aid in the study of scientific and technical development, and to illustrate the applications of physical science to technical industry. This is effected by the informative display of objects, diagrams, and photographs-so arranged as to illustrate in each Section the development which has taken place from past to modem practice. Many of the exhibits are so arranged that they can be operated by visitors or demonstrated to them. Others have been sectioned so that the internal structure can be clearly seen. A detailed descriptive label is placed by each object. The Collections have been augmented from time to time by loans and gifts from many sources, including many scientific and technical institutions, industrial firms, and also private individuals. In the Museum there are collections illustrating :- Textile and Agricultural Machinery. Hand and Machine Tools. Papermaking, Typewriting, Printing. Lighting and Illumination. Mining, Ore Dressing, Metallurgy. Glass and Pottery. Electrical Engineering. s Telegraphy, Telephony, Radio. Carts, Carriages, Cycies, and Mechanical Vehicles. Railway Construction, Locomotives, and Rolling Stock. Roads, Bridges, Lifting Appliances. Power Transmission, Pumps, Fire Protection. Building Construction, Heating, Water Supply, Sewage Disposal. Metrology (Weighing and Measuring). Steam and Internal Combustion Engines. Boilers. James Watt's Workshop. Marine Engines and Boilers, and Auxiliary Machinery. Harbours and Docks. Sailing Ships, Merchant Steamers, Steamships of War, Small Craft. Aircraft, Aero-Engines, and Aircraft Instruments. Mathematics, Astronomy. Chemistry, Photography, and K.inematography. Optical Instruments. Geodesy and Surveying. Meteorology. Terrestrial Magnetism, Seismology, Gravity, Atmospheric Electricity, and Tidal Phenomena. Applied Geophysics. Electrical, Magnetic, Acoustical, and Thermal Instruments. Time Measurement. Physical Phenomena, Properties of Matter, and a collection of Historical Apparatus formerly the property of the late Lord Rayleigh. There is also an extensive Science Library of books and periodicals, dealing with all branches of pure and applied science. The literature is available to the public for consultation in the reading-room, or obtainable on loan through the medium of an approved institution or industrial organization. 6 NoTE.-ln the following chapters, where reference is made to objects which are represented in the Museum Collections by originals or replicas, an asterisk • has been inserted in the text. RADIO COMMUNICATION ELECTROMAGNETIC WAVES HE possibility of electromagnetic wave propagation through the ether was predicted by Clerk Maxwell from his purely mathe­ T matical investigations. Heinrich Hertz, by a number of well­ devised experiments, demonstrated the truth of Maxwell's reasoning. The phenomena which had puzzled scientists for many years became immediately explicable. Maxwell announced his theory in x864 while Hertz supplied the practical verification in 1888. The earliest recorded evidence of the experimental observation of the effects of wave propagation through the ether is probably contained in an "Essay on Electricity" published by Adams in 178o. He noted that, at the moment of discharge of a Leyden jar, minute sparks passed between adjacent but unconnected conductors. The fact that such a discharge was not sudden, but consisted of a number of oscil­ latory surges, was appreciated by Riess and Henry some sixty years later, while Feddersen, in x86x, devised a rotating mirror experiment which showed definitely that this was the case. Paalzow and Lodge later demonstrated that the amplitude and periodicity of the oscillations depended on the electrical constants of the discharge circuit. Henry, in 1842, discovered that needles in a basement were magnetized by the discharge of an electrical machine 30 ft. above, despite the intervention of two 14-in. floors. Thomson and Houston, about 1877, were amazed at the ease with which secondary sparks from metallic objects could be drawn while they were working with a large Ruhmkorff coil. Edison, about the same time, noted some induced spark phenomena which he attributed to an "etheric force." The nearest approach to the true demonstration of " Hertzian waves " before the advent of Hertz was probably made by Hughes in 1879· He was experimenting with his microphones 1 and also with the induction balance. • While using the latter he was unable to get a perfect balance and, after