. The Bell System technical journal . covering the necessary range infrequency and intensity. A photograph of one of these sets is shownin Fig. 3. It consists essentially of a sensitive, stable superheterodynereceiver incorporating a calibrated attenuator at the input of theintermediate-frequency amplifier and a supplementary radio-frequencyoscillator from which a voltage of the frequency of the station undermeasurement can be introduced in the antenna circuit. The oper-ating characteristics of such an instrument have been described byFriis and Bruce.^ By means of a series of removable loops a
. The Bell System technical journal . covering the necessary range infrequency and intensity. A photograph of one of these sets is shownin Fig. 3. It consists essentially of a sensitive, stable superheterodynereceiver incorporating a calibrated attenuator at the input of theintermediate-frequency amplifier and a supplementary radio-frequencyoscillator from which a voltage of the frequency of the station undermeasurement can be introduced in the antenna circuit. The oper-ating characteristics of such an instrument have been described byFriis and Bruce.^ By means of a series of removable loops and coils, *H. T. Friis and E. Bruce, A Radio Field-Strength Measuring System forFrequencies up to Forty Megacycles, Proc. I. R. E., 14, 507-519; August, 1926. 128 BELL SYSTEM TECHNICAL JOURNAL the set shown is capable of measuring field strengths ranging fromapproximately to 7,000 mv per meter throughout the hand 250to 6,000 kc. Apparatus of this type is now in use by the radio inspec-tion division of the Department of Fig. 3—-Commercial field-strength measuring set. Range: 250-6,000 kc, ,000 mv per meter. In the light of this discussion of present trends in transmitter devel-opment, a brief description of some recent transmitting equipmentsmay be of interest. A particularly noteworthy example of currentpractice is the 50-kw. Western Electric transmitter, one of whichhas been placed in service within the past few months by the CrosleyRadio Corporation at Mason, Ohio. Views of this equipment areshown in Figs. 4, 5, 6, 7, and 8. The transmitter proper is shown RADIO BROADCASTING TRANSMITTERS 129 in Fig. 4. As will be seen, it consists of seven panel units with ascreen enclosure in the rear. The first unit on the left is the oscillator-modulator. This is essentially a low-power transmitter capable of anoutput of 50 watts and 100 per cent modulation. It is followed bythree push-pull stages amplifying modulated radio-frequency first power-amplifier
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
