. The Bell System technical journal . Fig. 41 41 and 42. In the first, the plate circuit of the tube forms a shuntacross a portion of the antenna inductance. As the grid potential isvaried, the antenna is, therefore, thrown more or less out of tune,with the consequent radiation of a variable amount of high frequencyenergy. Fig. 42 shows one of the most efficient modulating schemes thus fardeveloped. As the grid potential of the modulator tube A varies,causing a change in plate current through this tube, the plate voltage Low Frequency High Frequency Choke Choke. Fie. 42 applied to the oscillat
. The Bell System technical journal . Fig. 41 41 and 42. In the first, the plate circuit of the tube forms a shuntacross a portion of the antenna inductance. As the grid potential isvaried, the antenna is, therefore, thrown more or less out of tune,with the consequent radiation of a variable amount of high frequencyenergy. Fig. 42 shows one of the most efficient modulating schemes thus fardeveloped. As the grid potential of the modulator tube A varies,causing a change in plate current through this tube, the plate voltage Low Frequency High Frequency Choke Choke. Fie. 42 applied to the oscillator tube, B, fluctuates, because of the presenceof the low frequency choke coil. Under this condition of variableplate-voltage the oscillator gives a variable amount of high frequencyenergy to the antenna. When used for speech modulation thiscircuit is very efficient and gives good quality. The tubes A and Bare ordinarily of the same type. Many other modulating circuits have been designed, and thosegiven above are to be considered merely as illustrative of the generalmanner in which the properties of the vacuum tube may be appliedto the problem of 82 For other types of modulator circuits see a paper by R. A. Heising, Procd. Inst,Radio Engrs., Aug., 1921. THERMIONIC VACUUM TUBES 75 VIII. Thermionic Detectors Like the modulator the detector is a device for the production andseparation of difference frequencies. The object of modulation is, in general, to transform a high frequency ■—- and a low frequency ;^- 2tt 2ir into two high frequency
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