DISTORTION CORRECTION 479 



sharp change in the attenuation, such a maximum would not have been 

 produced. However, it is desirable to sharply attenuate the higher 

 frequencies as has been done here, for the reason stated above. It 

 is of interest to point out that the time-of-transmission which might 

 be expected for the corrected circuit from the low-frequency slope with 

 angular frequency of the steady-state phase, approximately r = .076 

 second, is actually the time at which the indicial voltage increases 

 most rapidly and has reached about .4 its final value, a quite satis- 

 factory agreement. 



4.3. Distortion Correction in Loaded-Cable Program Transmission 



Circuits 



Circuits which transmit programs originating at distant points to a 

 radio broadcasting station need to be of considerably better quality 

 over a wider frequency range than those used for ordinary telephone 

 transmission and must be reliable under various weather conditions. 

 Such circuits can be obtained economically with lightly loaded cable 

 pairs which have been corrected by terminal networks for each repeater 

 section. 



The design of distortion correcting networks applicable to a 50-mile 

 repeater section of 16-gauge H-44 cable follows. The section is 

 terminated at each end by a resistance R = 600 ohms, the generator 

 which impresses the voltage E having an internal impedance R. 

 Since the received voltage would be only .SE with the cable removed, 

 in this case we are interested in the ratio 



— /J— o— to 



.5£ " ^ ' 



where a then represents the insertion loss in napiers. 



If r and K are the propagation constant and iterative impedance 

 (here used at mid-section) of the loaded cable ^^ of length, /, it can be 

 shown that the transfer exponent is 



a + ih = r/ + Ml + ^2, (69) 



where Vl = propagation length, 



and 



2 L 2 



.-=^|l+il| + | 



^"^ = ' - ' m-" 



The above, of course, includes the effects of circuit terminations. 



1* Accurate computations for the propagation constant of the loaded cable were 

 made readily by means of an improved formula for cosh"^ (x -|- iy), given in 

 Appendix III. 



