Patent GB-580538-A (GB)
Title: Improvements in or relating to phase measuring apparatus
IPC: G01R25/00
Filed: 1943-11-01
Abstract: 580,538. Phase-difference measurements. SPERRY GYROSCOPE CO., Inc. Nov. 1, 1943, No. 18037. Convention date, Nov. 5, 1942. [Class 37] Apparatus for measuring the phase difference between two high-frequency test waves comprises a source of low-frequency waves, means for converting the high-frequency phase difference into an equivalent phase difference at the low frequency, and means for indicating this low-frequency phase difference and thereby determine the high-frequency phase difference, whereby this phase difference may be measured for varying high frequencies. An oscillator 11, Fig. 1 constitutes a source of high radio frequency oscillations at the frequency of which the phase shift produced by the apparatus 12 under test is to be measured. A second oscillator 13 supplies oscillations of a low frequency, which may be in the intermediate audio frequency range. The output from the oscillator 13 is modulated upon either the output wave of the oscillator 11, as shown, or of the test apparatus 12 in a balanced modulator 14, which suppresses the carrier frequency corresponding to the frequency of the oscillator 11. The output from the balanced modulator 14 is additively combined with the output from the test apparatus 12 in a combining circuit 16, the output from which is fed to an amplitude modulation detector and filter 17, which rectifies the wave and suppresses all direct current and all components exceeding the frequency of the oscillator 13. The detector 17 is of the square low type and produces an output of the frequency of the oscillator 13 and having an amplitude proportional to the cosine of the phase shift produced by the test apparatus 12. This is measured by an instrument 18 which may be directly calibrated in terms of phase shift. Alternatively the output of the combining circuit 16 may be fed to a frequency modulation detector and filter 19 and thence to an indicator 26 which may be calibrated in terms of phase shift. In a modification the outputs of the detectors 17, 19 are additively combined in a further combining circuit, the output of which has the same phase shift with respect to the output of the lowfrequency oscillator 13 as the phase shift caused by the test apparatus 12 to the high-frequency, oscillations. This phase shift is measured by a low-frequency phase meter. In a further modification, Fig. 5, an intermediate frequency oscillator 31 is provided having a fixed frequency separated by a substantial frequency difference from the high frequency. The-output of the oscillator 31 is combined with the output of the oscillator 11 in a frequency converter 32, the output of which has a frequency equal to the difference of the frequencies supplied thereto. This output is combined with that of the combining circuit 16 in a further frequency converter 33. The detectors 17, 19 may now be constructed to operate at a single fixed input frequency equal to that of the oscillator 31. The outputs of the detectors 17, 19 are combined in a combining circuit 27 and the phase difference between the output of this and that of the oscillator 13 is measured by a phase indicator 28. In another arrangement, Fig. 7, the high-frequency output of the oscillator 11 is combined with that of the low-frequency oscillator 13 in a frequency converter 36, the output of which together with that of the test apparatus 12 is supplied to a second frequency converter 37. The output of this is compared with that of the oscillator 13 by a phase indicator 28.