IN-BAND SIN(iLE-FREQUEXCY SIGNALING 



]31J 



15 



-20 



-30 



-35 



0.2 



0.3 0.4 0.5 0.6 0.8 1.0 2 3 4 5 6 



FREQUENCY IN KILOCYCLES PER SECOND 



8 10 



Fig. 2 — Signal-guard characteristics of 2,600-cycle receiver. 



Fig. 3. The dotted line shows a characteristic for a receiver with no 

 limiting, while the solid lines are for one with limiting. As shown, a given 

 large input would produce an output of Ei , the difference between the 

 signal voltage and guard voltage components, for the former case and 

 an output of E^ , which is about half as much, for the latter case. This 

 will be less likely to operate the receiver when applied for a short interval 

 of time, although either will produce an operation if applied long enough, 

 because either exceeds the just operate value Ei . 



Having established the basic design parameters of sensitivity, band- 

 width, guard to signal ratio, limiting characteristics and speed of re- 

 sponse it is important to know the relationship between signal imitation 

 and the frequency used for signaling. 



To obtain information on this subject a series of tests were made using 

 a number of guard channel receivers as nearly alike as possible except for 

 the frequencies of signal response, which were 800, 1,350, 1,800, 2,400 



