1182 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER, 1953 



Fig. 6 — Rear view of correlatograph showing rotating switch and delay line. 



PRELIMINARY RESULTS 



Tests on the complete correlatograph have only been carried far 

 enough to date to verify that the operation is as planned. Fig. 7 shows 

 correlatograms obtained with purely sinusoidal inputs of frequencies 

 200, 400, GOO, 800, 2,000, 3,000, and 4,000 cps recorded on the tape at 

 15 inches per second. In terms of the original signal the values of r extend 

 from zero to 12 ms. The profiles represented by the light and dark bands 

 should be rectified cosine waves starting with a peak at r = and 

 repeating at intervals of one half the period of the wave. In the total 

 range of r = 0.012 sec, a frequency of 200 cps should show 4.8 periods, 

 4,000 cps would show 96 periods, and in general / cps would show 0.024 

 f periods. The sudden changes in density parallel to the stripes were 

 caused by manual adjustments of the marking amplifier gain. 



Fig. 8 fchows correlatograms of a 1,000-cps sine wave embedded in 

 various amounts of flat thermal noise extending throughout the entire 

 input band. The sequence from bottom to top is noise alone, signal 

 and noise power equal, signal power down on noise power by 5 db, 

 10 db, 15 db, and 20 db. A long time correlation analysis would show 

 zero correlations for the noise alone except for small values of r. Short 



