80 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1952 



SYNTHESIS OF FREQUENCY-SWEEP PATTERNS 



To aid in the interpretation of the compHcated frequency sweep pat- 

 terns, a computor of the analogue type was built. This apparatus com- 

 bines four signal components, three of which are variable in delay and 

 amplitude, and presents the result on a cathode ray tube in the same 

 form as the actual frequency sweep patterns. Thus a particular pattern 

 can be synthesized on the computor and the number of components, 

 together with their path differences and relative amplitudes, read directly 

 from the computor dials. This is accomplished by generating four 600-kc 

 signals, three of which are phase modulated at 60 cycles per second. The 

 total phase deviation and relative signal amplitude are variable. The 

 four signals are then summed and displayed in vertical deflection on a 

 cathode ray tube having a 60-cycle horizontal sweep. 



The synthesis of the patterns of Figures 7(b) and 7(c) are shown in 

 Fig. 8. The upper synthesized pattern is simply a combination of two 

 components with relative amplitudes of 0.7 and 1 and a path difference 

 of two feet. The lower pattern consists of the reference component with 

 unity amplitude, a second component with an amplitude of 0.5 and a 

 path difference of 5.7 feet, and a third component with an amplitude of 

 0.2 and path difference of 0.8 feet. The similarity between the actual 

 and synthesized patterns is obvious. 



Fig. 8 — Synthesis of the frequency -sweep patterns of Figs. 7(b) and 7(c). 



