H - Electricity – 04 – B
Patent
H - Electricity
04
B
324/58.02
H04B 17/00 (2006.01) H04B 3/46 (2006.01)
Patent
CA 1038454
INSTRUMENT FOR MEASURING HARMONIC DISTORTION IN TELEPHONE TRANSMISSION Abstract of the Disclosure There is disclosed an instrument for measuring and displaying the harmonic distortion introduced during telephone line transmission. A frequency phase lock circuit is employed to generate disturbance-free in-phase and qua- drature signals of a received test tone, the disturbance- free generated tones being different from the transmitted test tone as a result of possible frequency shift along the transmission channel and phase shifts in the terminal equipment at both ends. The frequency of each of the in-phase and qua- drature signals is multiplied by the harmonic factor of in- terest (e.g., two). Each of the frequency-multiplied signals is then multiplied by the received test tone, and the two resultant signals, after low-pass filtering, are applied to the vertical and horizontal deflection plates of an oscillo- scope to form a display of the type disclosed in my U.S. Patent 3,906,173 (September 16, 1975. The display, in addition to reflecting a measurement of the frequency shift along the channel, also provides separate indications of the degree of harmonic distortion which occurs both ahead of the frequency shift (in the send terminal) and after the frequency shift (in the receive terminal).
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