496
8
from this source, and we trust that all facilities will be afforded that this work may proceed as rapidly as possible. We believe the Signal School to be conducting most important investigations at the present time in valve development, and to be likely to achieve results of the greatest practical application.
It is not expedient to state here much that is in preparation in connection with valve transmission, resulting from the work of the Signal School, but the following general information bears directly upon our conclusions.
The largest practical glass valves, when a group of three is used, deliver about 24 kilowatts into a suitable aerial, and this has given good communication (not, of course, a commercial service) to a distance of 2,000 miles. A silica valve was next made to the design of the Signal School, of more than four times the power of the glass valve, and still larger valves are designed. There is every reason to anticipate that with one grouping of these larger valves 75 kilowatts, and with another grouping 120 kilowatts, will be delivered into the aerial. Since the signal-value of the current generated by a valve is greater than that of the arc-current in the ratio of at least 1 to 1, owing to its greater purity of form, and since a 250-kilowatt arc delivers less than 120 kilowatts to the aerial, the last-named valve transmitter will be considerably more effective than a 250-kilowatt arc, as installed for instance, at Lyons. Since with valves 2 kilowatts in the aerial has given communication over 2,000 miles, with inefficient receiving apparatus, an aerial power of 120 kilowatts from valves, with efficient reception, may be confidently expected to give a good commercial service over this distance, and indeed probably much further.
The production of these valve groups, with the above-mentioned outputs, we are assured by the Signal School, may be regarded as a certainty within a short time; indeed they inform us that the aerial power may even be increased to. 240 kilowatts if necessary, a higher power than in any aerial to-day, with one possible exception. Nor is this all, for a more powerful valve still is being designed at the Signal School, but of this it is too soon to speak.
As regards the valve system of wireless transmission, mention must also be made of other advantages possessed by it. Whereas an arc generates several frequencies in addition to the fundamental frequency-in other words, several undesired and interfering wave-lengths in addition to the desired wave-length, causing unnecessary interference with other stations-the valve, when worked at a proper efficiency, produces only a aingle frequency. Even thus, the efficiency of valve working may be 66 per cent., as against about 40 per cent. for the are. It is not at all impossible that as the demand for long waves rapidly increases, the production of harmonics or other interfering frequencies may be internationally prohibited.
Again, the valve consumes electrical energy only while it is actually signalling, whereas the arc (until the inventors' claims before mentioned are proved) consumes energy equally during the transmission of the signalling dots and dashes and during the spaces between them. Again, the signalling key has to interrupt a much larger current in the arc system than in the valve system, and this "keying is a difficult problem awaiting solution in the employment of the larger arcs. This will be appreciated when it is explained that at a speed of 100 words a minute a heavy electrical current must be broken no fewer than twenty-five times a second. In the valve system the keying difficulty may be said hardly to exist, therefore this system lends itself much more readily than the arc to high-speed signalling. Finally, the valve installation will probably cost less than the arc system, and much less than the high-frequency alternator, while in a remote station the repairs of a break-down in the most vulnerable part of the plant of the valve system would only consist in replacing a defective valve by a new one, the work of a few minutes.
12. After this brief survey of the field of wireless science to-day, so far as concerns transmission, we pass to a consideration of the geographical aspects of an Imperial scheme of wireless communications.
The geographical distribution of the Empire clearly indicates the essential main lines of Imperial communication. Eastward these are: England, Egypt, India, Singapore, Australia, New Zealand; India-Bagdad; Singapore-Hongkong; Egypt- East Africa (Nairobi)-South Africa. Westward: Canada. South-westward: West Africa (Bathurst).
9
The distances are the following, measured from Oxford as a convenient inland point* :—
Oxford to Cairo
Poona
งง
West Africa (Bathurst)
Montreal
23
Poona to Singapore
"
Perth
Brisbane
Singapore to Hongkong
31
11
11
Port Darwin Perth Brisbane
Cairo to Poona
Bagdad
53
55
East Africa (Nairobi)...
West Africa (Bathurst) Windhuk
West Africa (Bathurst) to Windhuk
East Africa (Nairobi) to Windhuk
Montreal to Vancouver
Vancouver to Brisbane
Miles.
2,239
4,594
2,779
3,194
2,344
4,456
6,164
1,611
2,081
2,430
3,827
2,793
793
2,190
3,248
3,723
3,404
1,923
2,289
7,364
Poona is regarded by the military authorities as a suitable site in India. The former German Telefunken station at Windhuk, about 800 miles north of Cape Town, is equipped with buildings, masts, aerials, generating, transforming and lighting plant, &c., and could at comparatively slight cost, as we show later, be completed as an up-to-date wireless station. It is also adequately connected by land lines with Cape Town. We therefore suggest that the Government of the Union of South Africa could economically make it their terminal station, at least pending the wireless developments of the next few years, providing always that the range it would afford could be made to serve as a link in the Imperial chain. There is a service between Australia and New Zealand, and the development of this would, in any case, be a matter for the local authorities.
13. It will be observed that the above distances, disregarding Vancouver-Brisbane, 7,364 miles, a range we regard as outside the possibility of an efficient and economical commercial service under present conditions, fall broadly into two classes, which may be described as those of 2,000 miles and 4,000 miles respectively. England-Egypt- India Singapore-Hongkong; Singapore-Australia; and Egypt-East Africa-South Africa, are, roughly speaking, in the 2,000-mile class; England-India, Cairo-South Africa, India-Australia, are in the 4,000-mile class. The difference between the two, from the point of view of our definition of a satisfactory commercial service, is vital. The customary way to plan an Imperial wireless scheme has been to take a map of the world and a ruler, and to draw lines joining England and India, India and Australia, Egypt and the Cape, England and Canada, and Canada and Australia. The resulting diagram is gratifying and impressive. There only remained to measure the distances and make theoretical calculations of the power required to transmit wireless signals along these lines. If, when the stations were built, the power was found to be inadequate, then more power would have to be installed until the result was achieved. This may be described as the method of trial and error.
14. We find ourselves unable, after careful consideration, to adopt this procedure, and in arriving at our conclusions we have been largely guided by the history of long- distance transmission by wireless telegraphy. This begins in the year 1901, when by means of newly-discovered methods Mr. Marconi attempted to establish communication across the Atlantic, a distance of more than 2,000 miles, by a spark station of about 25 kilowatts. Experience gained on short distances had suggested that this power would be ample. But factors which become prominent only at great ranges presented unexpected difficulties, and the power of the transmitting station was increased step by step in successive attempts until in 1906 Marconi was using a power of about 75 kilowatts.
The figures of distance given in connection with different schemes of In perial communication vary considerably, and are often inaccurate. Those here given are Great Circle distances, in statute miles, that is, the shortest distance in each case, measured on the surface of the globe. They have been furnished to us by the Admiralty.
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