Abstract: There is disclosed a telephone line characteristic measuring instrument of the type described in U.S. Pat. No. 3,814,868, provided with an oscilloscope display. A signal representing the impairments induced on a test tone by a tele-communication transmission facility, without the test tone itself, is applied to the vertical deflection plates of an oscilloscope. The test tone, or one of its harmonics, is applied to the horizontal deflection plates. The resulting Lissajous patterns identify the source of a disturbance (e.g., amplitude modulation, phase modulation, white noise, etc.).

Abstract: There are disclosed instruments and methods for measuring envelope delay in a transmission channel which entail the simultaneous transmission over the channel of both a modulated reference tone and a modulated variable test tone. Unlike the prior art, in which the transmissions of the reference tone and the test tone take place alternately on the channel of interest, or in which the reference tone is transmitted over a separate channel, in accordance with the invention there is no need either to employ a second channel or to switch back and forth between tone transmissions. At the receiving end, the modulation signal on each tone is detected. The two modulation signals are the same at the transmitting end, and their phases are compared at the receiving end to determine the envelope delay of the channel.