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.
The Fine Structure of Television Images
There are described the necessary or preferred relations in the fine structure of television scanning, so chosen as to yield a system which is both theoretically ideal and practically optimum. The relations involve the width and spacing of the lines and the intensity distribution of circular scanning spots in both transmitter and receiver, which are correlated with the filter characteristics and the required width of the frequency band. A "flat" field of scanning, as distinguished from a "half-tone" field, is required at both ends, especially in the transmitter to suppress spurious large patterns otherwise generated in the scanning process. For equal horizontal and vertical "width of confusion," the nominal cutoff frequency of the system is found to be f. = fpN.' R/ V2N2 in which fp= frame frequency Ns= number of scanning lines, and R = aspect ratio. The over-all electrical characteristics require distortionless reproduction up to fcand permit a gradual cutoff between fcand 2fc. The "quadratic-sum rule" is derived for a special case and is offered as a generally approximate expression of the image width of confusion w in terms of the width of confusion of the respective individual components (object, optical, scanning, electrical): W = VWi2 + Wo2 + ± wn2. Based on the proposed television system of 30 frames per second, the full utilization of 441 lines requires a separation of 5.5 megacycles between picture and sound carriers. A separation of 4.