. (The) oscillation valve in the transmission and reception of radio messages . ess,giving the phenomenon known as beats. The number of beatsper second iS equal to the difference in frequencies of the twoforks. Thuf^, if two forks have frequencies of 230 and 225vibrations per seond they combine to give a sound which beatsfive times per second. Similarly, if two sources of undamped electricaloscillations of constant amplitude act on a circuit simul-taneously, one of frequency, say, 80,000 cycles per second, andthe other of 82,000 cycles per second, the amplitude of the resultant oscillation wil
. (The) oscillation valve in the transmission and reception of radio messages . ess,giving the phenomenon known as beats. The number of beatsper second iS equal to the difference in frequencies of the twoforks. Thuf^, if two forks have frequencies of 230 and 225vibrations per seond they combine to give a sound which beatsfive times per second. Similarly, if two sources of undamped electricaloscillations of constant amplitude act on a circuit simul-taneously, one of frequency, say, 80,000 cycles per second, andthe other of 82,000 cycles per second, the amplitude of the resultant oscillation will rise to a maximum 2,000 timesper seond. One of these sources of undamped oscillationsis of course the sending station, and the other raav be avacuum tube at the receiver, acting as a generator ofradio frequency currents. This is called beat orheterodyne reception. When rectified by a crystaldetector or vacuum tube the above would produce an audiblenote of frequency 2,000 in the telephone. The principle is shown in Fig. 14. w-^-^ \in^ o%Ci Hation S ~ ;jfuer\cy. ^ — Sigrxo,! Cor^^ Oscillations of frequency f, are superimposed onoscillations of frequency f2. The resultant oscillationshave a beat frequf^ncy of fi->f 2, or, in other words, themaximum value of the resultant oscillations is attainedfl-f2 times per second. When this resultant wave form () isimpressed upon any form of rectifying detector, most ofthe part of the wave below the zero axis is elimir^ted, ashas alreadv been explained. Thus the telephone diaphragmemits a tone correspondina: to the beat frequency fl— rectifying detector mav be the same vacuum tube whichis used to generate the local oscillations if we use aregenerative circuit similar to that described in Fig. is, one tube mav be used as a detector and generatorof local oscillations at the same time. This is called autodyne reception. The antennacircuit is tuned to the incoming sicnals, and
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