Image from page 505 of "The principles underlying radio communication" (1922)
Publisher: Washington, Govt. Print. Off.
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pletely modulatedwaves, using 500-cycle modulation, is described in Bureau ofStandards Scientific Paper No. 381. Heterodyne or other beat reception may also be advantageouslyused, as is usual with continuous waves. It is possible, though 500 ELECTRON TUBES. not as desirable, t use lor the plate supply voltage, alternatingcurrent of low commercial frequencies, such as 80 cycles. If itis necessary to use alternating current of as low a frequencyas 60 cycles, more satisfactory results will be obtained withheterodyne reception. The heterodyning of course destroys thepurity of the tone emitted by the transmitter, but gives muchbetter reception than a crystal detector or simple tube detector.If a low frequency, such as 60 cycles, is used, the received signalcan be improved by using a chopper at the transmittingstation. (See Sec. 211.) It is preferable, if possible, to usefor the power supply of the transmitter an alternating currentof an easily audible frequency, such as 800 cycles.
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WAVE. FORM OF OUTPUT CURRENT FROM TUBE. TRANSMITTER HAVING PLATE. SUPPLIED WITH 80O CYCLE! SINE WAVE ALTERNATING CURRENT Fio283 It should be noted that this alternating-current modulationof plate supply gives only one train of oscillations per cycle,corresponding to the intervals when the plate is positive—thatis, 60-cycle modulation of plate supply gives only the same tone asa fixed gap with a 30-cycle a.c. supply, since the latter givestwo trains of oscillations per cycle. By connecting the plates of two tubes to the secondary ter-minals of a single-phase transformer, one plate to each sec-ondary terminal, both halves of the cycle of supply voltagefrom a single-phase a.c. line can be used to operate the tubes.If this is done, it is desirable to use heterodyne reception. Itis also possible to effectively use two-phase or three-phasealternating current as plate supply in power generators; in thiscase the amplitude of the oscillations is much more nearly con-stant, and with three-pha
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