324 BELL SYSTEM TECHNICAL JOURNAL 



loaded line. They are useful in cases where it is desirable to extend 

 nearer the critical frequency the range of simulation possible by 

 means of the networks described by R. S. Hoyt.'^ 



Designs are given for mid-load and mid-section terminations. 

 Results for other terminations can be obtained by building out the 

 load or section. From an economic standpoint it might be pointed out 

 that the basic networks for the mid-point impedances to be described 

 each have seven elements, whereas corresponding designs based upon 

 Figs. 14 and 15 of Hoyt's paper would have six elements. However, 

 the new mid-load basic network which extends the range of simulation 

 requires only one-half the total amount of capacity but slightly more 

 inductance than that required by the corresponding Hoyt network; 

 the new mid-section basic network requires only one-half the total 

 amount of inductance but slightly more capacity than the corre- 

 sponding Hoyt network. 



4.1 Foundation of Designs 



The design of any simulating network usually involves two processes, 

 namely, a determination first of structural form and second of mag- 

 nitudes. 



The structural forms of the new designs follow readily from the well- 

 justified assumption that either mid-point impedance of a loaded line 

 in its principal transmitting band is approximately equal to the 

 corresponding mid-point impedance of a "constant k" low pass wave- 

 filter as the basic network, with the series addition of the impedance of 

 a supplementary network which simulates the additional impedance 

 introduced by dissipation at low frequencies. While this assumption 

 is really the same one which underlies the designs by Hoyt, the new 

 basic networks have considerably different forms and were derived 

 from wave-filter theory, which explains their inclusion in this paper. 

 In fact, the desired basic networks of Fig. 17 are immediately available 

 from the results of Part 3, being special cases of the networks of Fig. 

 15 which use the low pass wave-filters of Appendix H. 



The particular supplementary network chosen, one already con- 

 sidered by Hoyt but designed differently, has four elements, two 

 resistances and two capacities, and is known to have the desired 

 impedance characteristic. The same one will generally do for either 

 mid-load or mid-section impedance, as it contributes impedance only 

 at the lower frequencies of the range. 



The magnitudes of the elements of these networks are all determined 



""Impedance of Loaded Lines, and Design of Simulating and Compensating 

 Networks," R. S. lioyt, B. S. T. J., July, 1924. 



