DISTORTION CORRECTION 493 



within the range. The magnitudes of the elements corresponding to 

 the partial attenuation characteristic shown in Fig. 21, where R = 605 

 ohms, are 



Ri = 508.4 ohms; R2 = 105.8 ohms; 



The departures of the attenuation from the desired values are less than 

 .2 T.U. At the highest frequencies small coil dissipation tends to 

 improve this result. 



4.6. Phase Correction in Transatlantic Telephone System 

 At the receiving stations of the transatlantic telephone system it 

 is necessary to use phase correctors in connection with the antenna 

 arrays. These networks serve in two capacities, either {a) as artificial 

 lines or delay networks which build out the phase characteristics of 

 short transmission lines until they are equivalent to certain longer 

 lines used elsewhere in the system, or {h) as phase correctors which 

 secure adjustable and arbitrary phase characteristics when combining 

 the outputs of the antennae which form the array. For satisfactory 

 operation the phase correctors had to meet these design requirements. 



1. A constant iterative impedance of i? = 600 ohms. 



2. A continuously variable phase change which is proportional to 



frequency over the frequency range from 50 to 65 kilocycles per 

 second, the total phase change being from to 250 degrees at 

 50 kilocycles per second. 



3. Over any frequency band of 5 kilocycles per second in the range 



the variations should be less than .100 degree for the phase and 

 less than .025 T.U. for the attenuation. 



4. A balanced structure. 



In making the design it was found that the continuously variable 

 phase change to the desired maximum could be provided by means of 

 one variable section having a small phase constant and five fixed 

 sections of Networks 13, 14, and 16, Appendix IV. Designated in 

 terms of their phase constants at 50 kilocycles per second as in Fig. 22, 

 the variable section has a range of 0-15 degrees, while the fixed 

 sections have phase constants of 10, 20, 40, 80, and 160 degrees, respec- 

 tively. The variable section is normally required to give a maximum 

 of only 10 degrees but an extension of its range to 15 degrees is provided 

 so as to ensure phase overlapping at any transition point where a 



