N-1 CARRIER TELEPHONE SYSTEM 



429 



winding and the parallel aiding inductance value are equal to the mutual 

 inductance value to be annulled. If the loosely coupled windings of the 

 main inductors are connected in series aiding, then interposing the windings 

 of the annuling inductor in a series opposing fashion has the effect of adding 

 nothing to the inductance of the main windings plus mutual but annuls 

 the mutual in the equivalent T circuit. This is illustrated schematically in 

 Fig. 8. 





X 



DESIRED SIMPLE 

 LOW- PASS STRUCTURE 



La L 



X 

 X 



(-M) IS DEGRADING 



EQUIVALENT ELEMENT 



LINKING INDEPENDENT 



CIRCUITS 



(La+M) (Lb + M) 



rmp — 1 — nm^ 



r^^r^— I 



M-~. 



(La+M)+(M-M) (Lb + M)+{M-M) 



(WP — -r — ^^^^^ 



L, d L2 



Fig. 8 — Schematic illustrating the effect of introducing a mutual nulling inductor. 



Three designs of carrier frequency equahzers are used in the system. Two 

 of these provide the means for equalizing the slope of one cable span, amount- 

 ing to approximately 14 db. The equalization is divided between the trans- 

 mitting terminal (pre-equaHzation) and the receiving terminal (post-equal- 

 ization) in order to minimize the efifect of noise introduced along the cable. 

 The third equalizer is designed to compensate for the accumulated small 

 systematic distortions introduced by the cable spans and repeaters. This 

 "deviation" equalizer is required only on the longer systems involving ap- 

 proximately 10 or more repeaters. Each of these -three equalizers comprise 

 2 units similar in assembly to the carrier filters. 



