501
18
as it is based on technical considerations and would in our view, for reasons already given, have an important bearing on technical development.
32. From the point of view of wireless technics the Marconi Company's proposal is much too vague to allow of useful comment. Even the method of transmission
be adopted is not specified, but the possibility of the generation of powerful currents by the use of valves is mentioned. This we note with special interest, since on the Company's staff are several technicians of high competence in the design and use of valves. The suggestion of a Central Control Office is in accordance with modern practice. Distant control has been carried out in America, it is being planned in France, and the Post Office is arranging to operate the Leafield Station at first from Banbury and ultimately from the Central Telegraph Office in London. In any modern scheme the operators for both transmitting and receiving would be located at one point. An extreme claim is made for the "Franklin type of aerial," namely, that "so great is its importance that the scheme of wireless communications outlined in this Proposal depends fundamentally upon its adoption." The only Franklin patents we can trace of the nature suggested are No. 24098 of 1914 and No. 5783 of 1915. If these constitute the basis of the above claim it would appear probable that other methods of accomplishing the same object are known to wireless science. All such methods are based upon the employment of loop aerials, as explained hereafter. So far has this been developed that, following experiments carried out by the United States navy with the so-called " barrage receiver," Dr. Alexanderson, the American expert, has recently described an arrangement for a world-wide wireless scheme apparently identical in a large degree with that stated by the Marconi Company to be possible only by the use of the Franklin patent. He says: "The practical conclusion follows that the transmitting stations as well as receiving stations for each district should be grouped in centres, and these centres located relatively so as to make the directive neutralisation as effective as possible." We regret not to have been afforded the opportunity of examining Mr. Franklin upon this matter, and upon the results of his invention, if it has beez adopted anywhere in practice.
33. Passing from this topic we now proceed to consider further aspects of an Imperial wireless scheme. Hitherto, we have dealt almost exclusively with the trans- mission of wireless signals. The methods and results on the receiving side exhibit at least an equal advance during the past five years, owing to the development of the valve, and an acquaintance with the general principle involved is necessary for the appreciation of the latest wireless practice. When a valve is used for reception, the electronic current passing from filament to plate (see section 11 (d)) under the influence of a steady electrical tension is greatly modified by a feeble oscillating current in other words, by an incoming wireless sigual-applied between filament and grid. Thus, by the action of this relay or amplifier, the feeble arriving current is reproduced on a magnified scale and produces a sound in a telephone corresponding to each signal received; or, when further amplified by the same process repeated, is made to actuate automatic recording apparatus.
any
The valve in use to-day for wireless reception differs hardly at all from the type produced by the French Télégraphie Militaire early in the war, of which hundreds of thousands were used by the Allied forces. By its means, using a number of valves in cascade, enormous amplification of signals is possible, enabling any transmitting station to be heard at a greatly increased distance, or conversely, a much smaller transmitting power to be used for the same distance. This amplification has also rendered possible the reception of signals upon loop aerials-that is, inductive coils of wire wound on small frames-without the need of aerials supported upon high masts or of
earth connection. As a striking example of very great amplification of received signals by the use of valves, together with the employment of a loop aerial, we may say that the signals of Annapolis, U.S.A., have been audibly received in Paris, 3,800 miles distant, upon a coil of wire only 10 inches in diameter, the complete receiving apparatus standing upon a desk. Indeed, all scientific wireless reception to-day is by valves, and the use of elevated aerials for reception of long-distance signals may soon be abandoned altogether.
The loop aerial possesses a further characteristic of great importance in a general scheme of wireless communication. When the incoming wave is in the plane of the loop, the signals are at their maximum; when the loop is at right angles to the incoming wave, the signals disappear. As the loop is rotated, the signals vary in intensity, and the position of maximum intensity indicates the plane of propagation of the signal-wave. The co-ordination of two loop-aerial stations some distance apart
19
gives the point of origin. This is the principle of direction-finding, by which ships in fog are now given their exact position by wireless from the shore, and by which Zeppelins were guided across the North Sea. It will thus be understood that two simultaneous incoming wireless waves of the same power and the same length, which would "jam" each other's signals hopelessly upon an ordinary aerial, may be real independently upon two loop aerials, near but at an appropriate angle to each other. In an Imperial wireless system a multiple station for the reception of messages from different transmitting stations would be established on this principle.
C
34. Atmospheric electrical discharges (known in wireless language as "static," "parasites," "strays." "X's," or signals. In some latitudes, in summer, signals have often been unreadable from this atmospherics") are the bane of reception of wireless cause for twelve hours or more out of the twenty-four. India is oue of the worst sufferers, indeed to such an extent that it has been doubted whether this fact does not render au Indian site unsuitable for a relay wireless station for Australia. investigation of this problem is urgently required, but enough has already been done to indicate that a solution will be found, and again, by the use of valves. progress being made we may cite a recent statement of Dr. L. W. Austin, the eminent As an example of the head of the United States Radiotelegraphic Laboratory in Washington, to the effect that whereas, receiving at Washington on a simple loop aerial, the signals of high-power transmitting stations in Western Europe have been unreadable for about 2,000 hours during the year, by employing any one of four different static-reducing systems this time of unreadability can now be reduced to less than 100 hours, or less than 5 per cent. of the time formerly lost.
35. Finally, so far as concerns reception, while we have not ventured to specify a higher speed at first than 90 words per minute in the valve transmission over 2,000 miles which we recommend for official adoption, there is good ground for expectation that this may soon be largely surpassed. The Signals Experimental Establishment of the army at Woolwich, already mentioned, has achieved results of much interest and importance in automatic high-speed communication, and we trust its further investigations will be amply facilitated. By the use of new methods aud apparatus, wireless signals from a punched tape have been recorded upon a standard Post Office inking machine at a speed of 450 words a minute, and no difficulty is anticipated in controlling valve transmission at this speed by means of ordinary Post Office apparatus. Moreover, the selectivity of the receiving circuit is said to be so great that immunity from interference from other stations, and in a large degree from atmospheric disturbance also, is antici- pated. It may be added that the Post Office wireless staff, using the methods of the Signals Experimental Establishment somewhat modified, have recently transmitted by valve and recorded signals at the rate of 150 words a minute from London to Stonehaven (Kincardine), a distance of over 400 miles.
In our references to the development of the valve as a
long-distance transinitter, aud
to the development of high-speed transmission and reception, we have had in mind what has been achieved by the Government Departments. We have little information (except as mentioned on p. 3, footnote) as to what has been done by private enterprise in these directions, but we have no reason to suppose that the work of the Government departments has anywhere been surpassed.
36. Having thus passed in review the main aspects, historical, technical, geographical and financial, of an Imperial world-wide wireless service, we are now able to draw the practical conclusions which, in our opinion, follow. It should be borne in mind that the State already possesses the nucleus of an Imperial system in the Leafield- Cairo service, which is to come into operation in a few months, and in the ex-German station of Windhuk, and these must, of course, be utilised. We recommend, therefore, that a scheme of Imperial wireless communications be established in the following
manner.
The Leafield-Cairo are service now under construction should, we propose, be allocated to the African traffic. The Leafield station will, as and when required, handle such wireless traffic as may arise with foreign stations in Eastern Europe until this is otherwise provided for, but with this exception Leafield to be only the starting-point and terminus of duplex traffic with Egypt, and thence to East Africa and the Union of South Africa. A complete valve station, as herein specified, to be erected near Nairobi, East Africa, and this station to communicate duplex with Windhuk, which is adequately connected by land lines with Cape Town.
The former Telefunken station at Windhuk is already equipped with much plant suitable for a valve station, including two Otto Dietz 290 HP. oil engines. "The
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