GB646231A - Delay-distortion measuring apparatus - Google Patents

Abstract

646,231. Phase differences measuring. FRUITMAN, S. M. (Compagnie Industrielle des Telephones). March 9, 1948, No. 7261. [Class 37] The phase-delay/frequency characteristic of a network (which may be a transmission line) is measured by modulating at 3, Fig. 1, the reference frequency f o from 2 with a lowfrequency F o , and the variable frequency f from 6 with a low-frequency NF o (i.e. a multiple of F 0 ) at 7, applying both to the network 9, rectifying the output at 11, separating the frequencies F o . NF 0 at 12, 13, multiplying the frequency F 0 to NF o without phase change and comparing in 15 the phase of the two frequencies NF 0 . The initial phase at the input of the network 9 is maintained constant by adjusting phase-shifting device 5 in accordance with the indications of a meter 15<SP>1</SP> fed similarly to meter 15. Preferably the oscillation NF o is developed at 4 by frequency multiplication of the frequency F o at 1. The meter 15 may be a null instrument or a cathode-ray oscillograph, the phase-difference being reduced to zero by phaseshifting networks between filters 12, 13 and meter 15, Figs. 2, 2, not shown. Where high accuracy is required, both demodulated frequencies NF o may be further multiplied before application to the meter.