. The Bell System technical journal . ulating frequency. This will be, of course, a direct measure ofthe envelope delay. From the preceding discussion of some of the principles involved inthe transmission of modulated waves, it is evident that the phase shiftduring transmission of the simple envelope considered is equal to onehalf the difference of the phase shifts of each of the sideband fre-quencies. This phase shift of the envelope is then the difference inphase shift for a definite frequency interval and is quite convenientfor the measurement of the envelope delay. The envelope delay somea
. The Bell System technical journal . ulating frequency. This will be, of course, a direct measure ofthe envelope delay. From the preceding discussion of some of the principles involved inthe transmission of modulated waves, it is evident that the phase shiftduring transmission of the simple envelope considered is equal to onehalf the difference of the phase shifts of each of the sideband fre-quencies. This phase shift of the envelope is then the difference inphase shift for a definite frequency interval and is quite convenientfor the measurement of the envelope delay. The envelope delay someasured is that for some frequency intermediate between the two MEASUREMENT OF PHASE DISTORTION 539 sideband frequencies and, although it is not accurately the envelopedelay for the carrier frequency, it may be taken as such for all practicalcases when the modulating frequency is taken small enough so that theslope of the phase shift-frequency curve for the carrier and the twosidebands may be considered constant. AUXILIARYPHASE SHIFTER. PHASE SHITTER Fig. 7—Arrangement for direct measurement of envelope delay. shifter shown R = SOttL = I/SOttC. In the phase Fig. 7 shows schematically a circuit for measuring the envelope delayby measuring the phase shift of the envelope.^^ The carrier frequencyis modulated with another frequency, 25 cycles for example, and thentransmitted through the system to be measured. At the receiving endan ordinary amplifier-detector is used to demodulate the received waveand obtain the modulating frequency. This source can then becompared in phase with a reference frequency which is obtained fromthe original source. In order to avoid including the effects of themeasuring apparatus itself, the change in phase shift so measuredthrough the system under consideration should be compared with asimilar measurement made with an artificial resistance line substitutedfor the system under test. The difference of these two will, of course,be the phase shift suffered
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