Presented by the Postmaster-General to LONDON: PUBLISHED BY HIS MAJESTY'S STATIONERY OFFICE. To be purchased directly from H.M. STATIONERY OFFICE at the following addresses: 15, Donegall Square West, Belfast; or through any Bookseller. 1927. Price 2d. Net. Cmd. 2858. COMMITTEE ON TRANS-ATLANTIC WIRELESS TELEPHONY. Admiral of the Fleet Sir HENRY B. JACKSON, G.C.B., K.C.V.O., F.R.S., R.N., Chairman of the Radio Research Board (Chairman). Major General Sir FREDERICK H. SYKES, G.B.E., K.C.B., C.M.G., M.P. R. A. DALZELL, Esq., C.B., C.B.E., Director of Telegraphs and Telephones, General Post Office. W. H. ECCLES, Esq., D.Sc., F.R.S., President of the Institution of Electrical Engineers. F. GILL, Esq., O.B.E., M.Inst.C.E., Past President of the Institution of Electrical Engineers. E. H. SHAUGHNESSY, Esq., O.B.E., M.I.E.E., Assistant Engineer-in-Chief, General Post Office. Lt. Col. A. G. LEE, M.C., M.I.E.E., (Secretary). Terms of reference. REPORT. 1. We were appointed by the Postmaster-General in March, 1923, with the following terms of reference : To consider in the light of recent progress in wireless science the possibility from a technical standpoint of Trans-Atlantic Wireless Telephony of sufficient reliability for commercial use, and to advise what practical steps, if any, can at present be taken to develop this means of communication." Progress in wireless science. 2. The development of the Thermionic Valve and its application to wireless transmission and reception had opened up possibilities of trans-oceanic wireless telephony which had been beyond practical attainment previously. In 1915, the American Telephone and Telegraph Company, by connecting together a large number of small valves which were then available, succeeded in transmitting speech across the Atlantic from Arlington, U.S.A., to Paris, and between 1915 and 1923 developed what is known as the "single side band, suppressed carrier" method of working in wireless telephony, an invention which is designed to reduce the number of wavelengths required for telephonic communication and, at the same time, offers very considerable advantages in the utilisation of power required for transmission. Attention was also paid to the development of a large power valve, and to the production of a water-cooled valve of 10 kilowatts continuous and reliable output. These advances, together with a large number of other important improvements, opened up possibilities of long-distance wireless telephony. With larger valves and improved technique, the Company again achieved one-way Trans-Atlantic telephony, and on 15 January, 1923, a large audience at the works of the Western Electric Co. (now Standard Telephones and Cables, Ltd.) at New Southgate, London, heard the voices of the speakers in New York quite clearly and loudly, speaking at pre-determined times over a period of two hours. Preliminary experimental work. 3. The preliminary work of the Committee was devoted to obtaining data for outlining the problem upon which it was engaged. It was known that wireless signals across the Atlantic varied in strength from hour to hour and day to day, and that the disturbance due to what are known as atmospherics varied also at different times of the day and at different seasons of the year. The American Telephone and Telegraph Co., the Radio Corporation of America, the International Western Electric Co. (now International Standard Electric Corporation) and the Post Office Engineering Department offered their co-operation in the necessary experiments. To obtain the required data, it was decided to make measurements in this country of the strength of signals from America, and the strength of the atmospherics, each week-end, over a complete 24 hours in each case. These measurements were continued to the end of 1926, and numerous records of the conditions likely to be met in giving a commercial service were thus obtained. At the same time, the Post Office wireless stations, Leafield, Northolt and latterly, Rugby, transmitted signals to America, where similar measurements on signal strength and atmospherics were also being made. The special signals from America were sent from the Radio Corporation station at Rocky Point, Long Island. Speech was also transmitted from this station and measurements of the deteriorating effect of atmospherics on the intelligibility of speech were made in this country. Arrangements were also made concurrently for the Post Office Engineering Department to instal at Chedzoy, Somerset, a receiving antenna, seven miles in length, for the purpose of gaining experience of the value of this type of antenna in combating atmospheric disturbances. Installation of 200 k.w. telephony transmitter at Rugby Wireless Station. 4. After the preliminary data from these measurements became available, it was possible to decide upon the size and 0 (33)28448 Wt 1884-8 6 875 5/27 A 2 type of transmitter and the receiving arrangements which would be necessary in order to attempt a commercial telephone service between England and America, and the Committee recommended the Postmaster-General to instal a 200-kilowatt telephony transmitter at the Rugby wireless station for this purpose, and in order to see what further difficulties would be encountered. It was hoped that this transmitter would, if successful in the experimental stage, be suitable for commercial working later. The telephony transmitter apparatus was ordered by the Post Office from the Western Electric Co. (now Standard Telephones & Cables, Ltd.), who installed it at Rugby. A separate antenna and earth system and the necessary oscillating circuits for the telephony installation were also erected by the Post Office. It was thus possible to obtain the advantages of conducting the initial experiments at the Rugby station, where the high masts and the necessary power and certain plant were already available without additional expense. The telephony transmitter installed at Rugby comprised modulation equipment and power amplifiers. The modulation equipment converts the speech currents arriving over the cable system from London into weak wireless signals, using the "single side band suppressed carrier system" already mentioned. After the wireless signals are produced in the modulation equipment, they are amplified in three stages for transmission from the antenna. The power amplifier consists of 30 water-cooled metal-glass valves, each of 10 kilowatts rating. This transmitter was designed on somewhat similar lines to that which was already in use by the American Telephone & Telegraph Co. at the Rocky Point Station, full advantage being taken of the experience gained in the working of that installation. The British installation was ready for trial early in 1926, and, after preliminary tests had been made, two-way conversation between England and America was first attained on 7 February, 1926. Installation of receiving arrangements at Wroughton and in the United States. 5. Improvements had also been made in the receiving arrangements. In this country, a double receiving antenna had been erected at Wroughton, near Swindon, in order to be near the main underground telephone system from London to the West of England. Measurements and tests carried out in Scotland in 1925 and 1926 indicated that a considerable improvement would be obtained by reception in the North, and another receiving antenna is being built at Cupar, which it is expected will be ready shortly. In America, also, experiments had been made, using a receiving antenna at different locations. As a result, it was found that the more northerly the location the greater was the freedom from atmospherics, and the American Telephone & Telegraph Co. |