Telegraph Distortion on High-Speed Frequency Shift Data Transmission Systems

First, the distortion due to the telephone channel is calculated by considering the instantaneous frequency of the transmitted signal, the telephone channel being defined in terms of its frequency characteristics: attenuation and group delay. The results are easily obtained when the signal is recurrent. Calculations have been carried out on a particular binary signal, for some typical telephone lines, the results being presented as time variations of instantaneous frequency and amplitude. Then, consideration is given to the distortion coming from other disturbances, such as frequency stability, imperfect limitation and, more specially, noises. Two typical sources of noise are examined: noise consisting of a sine wave, and white noise. Distortion is evaluated in each case by calculating the maximum disturbance, this being done for an ideal binary signal, and also for a signal already affected by some typical inperfection of the telephone channel.