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Radio Telegraphy
343
efificiency of the high power single units will be as good as that of the multiple units, and the work on the large tubes is being considered so far as experimental.
EFFICIENCY OF TRANSMITTERS
IN transmission work, a large amount of investigation has been carried out during, the last two years on the efficiency of the circuits and in regard to the best way of utilizing the available energy.
Considerable increases in efficiency have been obtained in the aerial or antenna circuits and also in minimizing the losses in the attendant loading coils, and the latest results indicate that it is possible to obtain efficiency of radiation into space as high as fifty per cent, on wavelengths as long as 20,060 meters, when, in this particular case, towers of a height of 250 meters would, of course, have to be used, owing to the length of the wave.
Very careful investigations have been carried out by Mr. H. W. Round of all the losses in the loading coils and other parts of the tube circuits, and actual measurements on considerable power have shown that an over-all efficiency from the input power on the plates of the tubes to the aerial of seventy per cent, is possible with a complete avoidance of harmonics, that is, an efficiency from the power input to the plates of the tubes to actual radiation into space of about thirty-five per cent.
On shorter wave stations it is quite practicable still further to increase this efficiency
although possibly it is hardly worth the extra expense involved. We have at present one station in England working on a 3,000 meter wave length with a height of mast of 100 meters which has an efficiency from plates to radiation into space of 40 per cent.
In high speed transmission, we are maintaining public services at 100 words per minute to two places in Europe, namely, Paris and Berne, using a single aerial transmitter with two wavelengths on the same aerial, and although the operation of utilizing a single aerial for two wave lengths is not an advisable one for high power work, it has certain points to recommend it in medium power work, where the consequent loss of efficiency can be made up for by a slight increase of power.
These two waves are working duplex to both Paris and Berne and practically all traffic is taken on printing machinery, although there are occasions when, because of static, reception has to be done on undulator tape, and, in some rare cases, on the telephones, by sound.
The reception at these shorter distance stations is carried out by means of a cascade arrangement of high and low frequency tuned amplifier circuits attached to the directional aerial system of the Bellini type, arranged for unidirectional reception when necessary. Very great care is taken in the receiving circuits to shield them so that the tuned circuits come well into action and to prevent any direct effect or influence of the aerial on circuits other than those intended to be acted upon. The char
Marconi's yacht, the Elettra, which is fitted with a very complete radio laboratory. While the yacht was in the Hudson River Mr. G. Mathieu, who accompanied Marconi, received signals from Europe with remarkable intensity, by a system of amplification he has perfected, using a loop antenna
© Kadel & Herbert