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Page:Popular Science Monthly Volume 89.djvu/645

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Popular Science Monthly


��Lieutenant H. C. Gawler, the cliicf radio inspector of the New England District, and Inspector Cheetham, the Marconi expert, were even more sur- prised when they began sending from their improvised station, for the rephes they received showed that they were able to send a distance of 150 miles, or six times as far as would have ordinarily been the case. The normal record for a governmiMit field set is 44 miles, but it is probable that an ordinary field out- fit can be made to send to a distance of 300 miles or more, when a kite-supported aerial is employed and if all conditions are favorable. It is possible to send up the kites and the aerial when there is very little breeze.

In last summer's Plattsburgh ma- neuvers the signal corps were shown that they could increase the range of their field set by about 200 miles if kite aerials were used, and also that they could do this almost any day. When it is impossible to send up kites, it is proposed to use a small hydrogen balloon. A later test of the improved pack set at Fort Leavenworth demon- strated that it is now possible to send even farther than was believed pos- sible. — ^Stanley Y. Beach.

��A New Spark-Gap for Wireless Telephony

IN order to transmit speech by wireless it is necessary to produce continuous waves, or, as a substitute, groups of electromagnetic waves at a very high

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��A special gap wich highly cooled sparking surfaces inclosed in a gas-filled chamber

frequency. The transmitter should be uniform in operation, so that a practical- ly continuous stream of radiant energy

��will flow out from the sending antenna. The various forms of arc generators, when very carefully adjusted, or now familiar high-frequency alternators, can be used in this way. It has been sugges- ted by various inventors that sparks occurring at very high frequencies might


��A diagram showing how the telephonic sparker may be interposed in the line

also form a basis for radio-telephonic power generation; many forms of quenched and rotary-gaps for this pur- pose have been proposed.

In U. S. Patent 1,173,562 there is shown a special gap having small highly-cooled sparkling surfaces enclosed in a chamber through which passes carbon dioxide gas. The inventor, W. T. Ditcham, points out that if large electrodes are used the spark will not remain sufficiently constant for the transmitted speech to be clearly articu- late. In his new gap, which is shown in Fig. I, the spark is restricted to the ends of the small plugs B, which are firmly set in the shafts 5' and B-. These rods carry cooling flanges D, and are secured to the walls H of the gap chamber /•" by the flanges G, I. Fresh carbonic acid gas is fed through the tubes K^, K' and serves to cool the gaps.

Figure 2 shows one of the circuits in which the new discharger may be used. M represents a direct-current generator, of about 1,000 volts, which is connected through resistance A^ and choke-coils O, O, to the terminals of the gap A. The high-frequency circuit is compo.sed of the gap, the condenser P and the primary Q; to this last-named coil is closely coupled the secondary R, which, with the microphone V, is connected between the antenna 5 and ground W. The two oscillation-circuits are not tuned to the same frequency as if measured separately, for the best transfer of

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