File:The principles underlying radio communication (1922) (14571438499).jpg

Identifier: principlesunderl00unit (find matches)
Title: The principles underlying radio communication
Year: 1922 (1920s)
Authors: United States. National Bureau of Standards Ould, Richard Sheldon, 1889- United States. Army. Signal Corps
Subjects: Telegraph, Wireless Radio
Publisher: Washington, Govt. Print. Off.
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form the successive gaps. The number ofgaps is determined by the voltage, allowing about 1200 volts foreach gap. Eight or ten gaps are usually sufficient. (See alsoSection 123, page 279.) Until comparatively recently the quenched gap has not beenin use on a supply frequency as low as 60 cycles per second. Ithas recently been found possible to use quenched gaps with 60-cycle supply and still get smooth tones and excellent communi-cation by the use of a variable series resistance in the primarycircuit of the transformer, and also by employing a transformerof the resonance type with an unusually high secondary voltage.By altering the series resistance, the spark rate may be changedas desired, as to 60, 120, or 240 per second. This adjustment issomewhat critical and difficult to maintain exactly under condi-tions where line voltage variations are encountered. Suchvariations of line voltage result in a roughening of the tone,which does not, however, seem to seriously affect communica-tion.
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Fig 1S4 —Radio telegraph transmitting and receiving set witla queucbedgap. Signal Corps Type SCR-49. (Pack set.) 1. Quenched gap. 8. Loading inductance. 2. Transmitting condenser. 9. Primary inductance. 3 Safety ^^ap l^- Secondary inductance. 4 Transfol-nier 11- Common terminal of primary5. Receiving set. «iid secondary. 6 Kev 12. Antenna switch. 7 Tool box 13. Ammeter in counterpoise lead. 359 360 TRANSMITTING APPARATUS. One advantage of the quepched gap is its quietness of opera-tion, in comparison witli the noisy discharge of tlie ordinarytypes of rotary gap. This is because of the very short gaps,and the inclosure of the spark. When 500-cycle supply is used with a quenched gap. it is customary to so adjust the voltage and the number of gaps that there is one discharge per half cycle, or 1.000 sparks per second. (See Fig. 185.)Unless the antenna resistance is very high, there will usually be found with any quenched gap critical values of couplingbetween the primary and secondary

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