A New Principle for Measuring Electrical Length and Deviation from Linear Phase
This paper presents a unique way to measure the equivalent electrical length of a network as well as its deviation from linear phase. The measurement technique used is based upon a variable length transmission line simulator, built into the IF-structure of a 1.3 GHz Network Analyzer, but can be applied to higher frequencies. The new method allows to insert much more electrical length than the mechanical line stretchers do, without disturbing the measurement with additional mismatch errors. In addition to a calibrated readout of the equivalent electrical length in meters, the deviations from linear phase of a network can be presented very accurately in a real time swept display.
The Interpretation of Amplitude and Phase Distortion in Terms of Paired Echoes
In picture-transmission systems, such as television and facsimile, the signal transients are noticeably distorted by small amounts of amplitude and phase distortion. There has been developed a simple method of estimating the effects of such distortion from inspection of the amplitude and phase curves. The distortion is regarded as made up of a pattern of echoes, each echo corresponding to a small amount of distortion of both kinds. The separate interpretation of amplitude and phase distortion requires pairs of echoes, those of each pair being equally displaced in time before and after the signal output. This is called the "method of paired echoes." Amplitude distortion corresponds to symmetrical "positive" pairs whereas phase distortion corresponds to skew-symmetrical "negative" pairs. A complete and exact theory is presented on the basis of a small amount of distortion. The method of paired echoes is most useful in the interpretation of phase curves and the determination of the tolerance of phase distortion.
Phase distortion in telephone apparatus
This paper shows that if, over its transmitting range, the phase shift, B, in radians, of a four-terminal network may be written B = a 0 + a 1 ω (ω = 2πx frequency in cycles per second), there is no phase distortion if a 0 = N, N being any integer. However, there is a delay, for any signal, given by dB/dω = a 1 (seconds). If N is not an integer, there is a delay, a 1 , and in addition a distortion, which distortion, generally for speech and music, may be neglected. Typical phase characteristics for lines, filters and all-pass networks are shown. In general over their transmitting range, such phase characteristics which usually are curved, may be regarded as the sum of two characteristics, a straight line having a slope corresponding to the minimum slope of the original and which introduces a delay without distortion and a curved portion to which all of the distortion of the signal may be ascribed. Oscillograms are given showing the distortion for a loaded line and for band filters for a signal which is of the form y sin (ω 0 t + θ) between t = 0 and t = T and zero for all other time. A description is given of the means employed for reducing the amount of phase distortion in telephone cable and in low-pass filters in circuits used for program transmission and regular telephone service. Also, phase distortion in repeaters and transformers is described. Brief reference is made to the problem of phase distortion in telegraph, picture transmission, and television circuits.