CARRIER TELEGRAPH METHODS 



507 



level compensated on-off, frequency-shift, single-sideband with — 6 db spac- 

 ing carrier. 



In both Figs. 8 and 10 there appears to be considerable difference between 

 the distortion vs. carrier frequency characteristics of the two-source and 

 one-source two-band arrangements with limiter. The two-source arrange- 

 ment was better for large carrier frequency variations, and the one-source 

 two-band arrangement was better for small carrier frequency variations. 



50 



U 40 



-60 -50 -40 -30 -20 -10 10 20 30 40 50 60 



MEAN CARRIER FREQUENCY IN CYCLES PER SECOND (DEPARTURE FROM NOMINAL VALUE) 



Fig. 11 — Distortion vs. mean carrier frequency characteristics of wide-band 

 frequency-shift arrangements. 



The difference between the performance of these two arrangements was 

 partly due to interference between sidebands in the two-source arrangement 

 as previously mentioned, and partly due to the difference in the sending 

 arrangements used. In the case of the two-source sending arrangement 

 shown in Fig. 2, the sidebands of the marking and spacing paths were sepa- 

 rated by the sending filters, and a small shift in carrier frequency affected 

 each branch similarly, and relatively little bias or distortion resulted. In 

 the case of the one-source two-band method also shown in Fig. 2, the side- 



