Journal of the Society of Motion Picture and Television Engineers (1950-1954)

ECHO DELAY IN PICTURE ELEMENTS = O)ftT/ 7T I I °if Fig. 14. Relation between echo amplitude and echo delay for double-excursion K = 0.1 in characteristic. however, to leave the approximate equations (9) and (11) of the Appendix, upon which equations (2) are based, and use the exact equations (8) and (9). This is because in this region of echo delays a tends to become large. When the exact equations are used, the shape of the curve for a is affected, as well as its magnitude, by the constant values chosen for R and <£. These relationships have been plotted in Figs. 12, 13 and 14. The figures illustrate the echo amplitudes, for various echo delays, that are set by a fixed excursion in transmission characteristic within the nominal passband. In Fig. 12 this double excursion is set at K = R = 1 for the amplitude response, and at K = $ = 1 radian for the phase. In Fig. 13 it is set at K = 0.3, and in Fig. 14 at/T= 0.1. In the plots the relationship presented between echo amplitude and echo delay is not the compromise which was mentioned earlier in the discussion. A separate figure for a is in each case derived, respectively, from equations (8) and (10) of the Appendix. The use of the exact equations causes a further complication. In the approximate equations (2) the results are the same regardless of whether the assumed echo is positive or negative. When the exact equations are used this is no longer the case, and separate plots have been made for positive and negative echoes in Figs. 12, 13 and 14. The trend of the curves in Fig. 12 is rather complicated because of the large Pierre M ertz: Television Transmission Echoes 587