An envelope delay-measuring instrument in the audio-frequency range

IT HAS long been recognized that careful attention must be given to the amplitude response of all types of communication systems throughout the useful frequency range. Other effects arising from system phase characteristics became evident as circuit lengths increased. These effects, resulting from phase distortion, persisted even after perfect correction had been made for amplitude distortion. In telephony for relatively short distances, phase distortion was usually of small importance. However, with the increased length of circuits phase distortion over the essential range of frequencies was found to play an important role. In landline code telegraphy, d-c or carrier, the effects of phase response are negligible compared with amplitude response. In any event, the processes of signal regeneration, sampling, or pickup, and code translation provide a “margin” within which distortion effects are absent and a perfect printed reproduction of the telegraph message is obtained.