. The principles underlying radio communication . controls, however, are used for the modulating antenna current is not necessarily the condition formaximum speech signal. Some sets are provided with a low-power lamp as a modulation indicator in the lead to the plateof the oscillator tube or in the lead to the generating system ; thelight is brighter during modulation than where there is no is because the heating effect of a pulsating current ia OPERATION OF RADIOTELEPHONE SETS. 527 greater than the heating effect of the direct-current portion ofthe pul
. The principles underlying radio communication . controls, however, are used for the modulating antenna current is not necessarily the condition formaximum speech signal. Some sets are provided with a low-power lamp as a modulation indicator in the lead to the plateof the oscillator tube or in the lead to the generating system ; thelight is brighter during modulation than where there is no is because the heating effect of a pulsating current ia OPERATION OF RADIOTELEPHONE SETS. 527 greater than the heating effect of the direct-current portion ofthe pulsating current would be by itself. Most sets are also pro-vided with a coupling between the transmitter equipment andthe receiver, so that the operator by hearing his own speech mayknow whether the quality is good. As a general rule theantenna current will not vary appreciably during modulationif the speech quality is good. Special types of radiotelephone sets have been constructed forduplex or two-way conversations, so that communication can LU. Fig 233 Signal Corps, U. S Army Radio Telephone SetBox, Type SCR 67 Transmitter Diagram be maintained as in land telephony without throwing an an-tenna switch from transmitter to receiver. In these sets meansare provided so that an outgoing message will not greatlyaffect the receiver phones, while an incoming message will. 210. Practical Forms of Apparatus.—A schematic diagram ofa complete radiotelephone transmitter such as is used by theSignal Corps in short range work is shown in Fig. 293. Thegenerating system, to the right of the points marked 0+ and&—, may be described as a system having the oscillating circuitdirect coupled in parallel with the oscillator tube, both beingfed through the radio-frequency choke coil Lu The feed back53904°—22 34 528 TUBES. to the grid of the oscillator tube is by capacity coupling. Acondenser C, serves to transmit the variation of voltageacross C* to the grid without having the gr
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