30204 Comparator The comparator circuit changes the amplitude modulated pulses from the converter into a time-modulated pulse-train. The output pulses of the converter are transformer coupled into the comparator unit, where they are amplified by VY-10. The pulses out of this amplifier appear on the piate of the discriminator diode, V-11l. The cathode potential of this diode is varied linearly from a minimum to a maximum voltage by R-37 whose shaft is motor driven at a rate of l cps. ‘The limits of this variable voltage are set by R-36 and R-38. Only those pulses on the plate of V-11A larger in amplitude than the cathode potential pass through the diode. Therefore, each second a train of pulses of decreasing amplitude are produced (Fig. lie). These are fed to an amplifier (V-12) which drives a univibrator (¥-13), whose output is a constant amplitude pujse. R-38 is adjusted so that at zero signal on the bridge results in the production of five pulses large enough to trigger the univibrator. With one volt on the bridge about 95 pulses are produced. Since the input rate is 120 pulses per second, no pulses are transmitted for at least one quarter of a second. A large sharp pulse is produced by the potentiometer as the wiper leaves the winding on the high end, therefore capacitor C-16 must be kept small so that it will discharge twfore the wiper again contacts the winding on the low end to beginning of the next cycle. C-18 acts as a by-pass for the residual spike and reduces its amplitude to a level which will not affect the pulse discriminators. The output of the univibrator, Figure lid, is a constant-amplitude time modulated pulse train, whose length is proportional to the = 33 =