932 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1953 



The capacitors shown dotted are parasitic elements which must be com- 

 pensated for by modifying the design values of the other elements. This 

 group of sections has an insertion loss varying from 2 to 12 db across the 

 pass band of the filter, caused by the dissipation of the elements. This 

 loss, of course, must be taken into account in the design of the loss 

 equalizer sections. 



The objective is to obtain equivalent video transmission through the 

 terminal flat to limits varying from d=0.02 db to dzO.lO db, depending 

 upon the frequency characteristic of the deviation. To achieve this, 

 close control of the dissipation loss is essential. The inductor losses which 

 cause the major part of the delay equalizer loss characteristic vary up 

 to ±15 per cent from nominal values. As a means for controlling inductor 

 Q to ±0.5 per cent or better, a "Q adjusting screw" is employed. The 

 inductors are solenoids wound on molded tubes with a threaded hole 

 through the center. A threaded magnetic dust core is used for induc- 

 tance adjustment. Its travel can be limited to the distance from the 

 center to one end of the form without losing adjustment range. By 

 introducing an additional core made of solid magnetic iron into the field 

 of the solenoid, using the opposite end of the form, an adjustment is 

 provided which reduces the Q in a continuous manner as the second screw 

 is advanced into the form. The reduction in Q is caused by the losses in 

 the iron, and normally these would cause a reduction in inductance also. 

 However, the permeability of iron causes an increased concentration of 

 field which tends to increase the inductance. A balance between these 

 tendencies to decrease and to increase the inductance is obtained by 

 controlling the geometry of the Q adjusting core. As a result, a reduction 

 of up to 50 per cent in Q can be obtained, accompanied by a change 

 of less than one per cent in the inductance. Models of the inductor and 

 the adjusting screws are shown on Fig. 12. This adjusting screw in con- 

 junction with the magnetic dust core provides an accurate and economical 

 means for adjusting simultaneously both inductance and dissipation in 

 each inductor of the delay equalizer. 



The flat transmission level for the upper sideband and the shaped 

 cut-off" for the vestigial sideband were obtained by including loss equal- 

 izer sections, assuming Q factors for the all-pass sections of about 20 

 per cent less than the nominal Q of the inductors. As a final step in the 

 design, the Q factors were modified to absorb in the loss of the all-pass 

 sections the residual loss distortion uncompensated by the loss equalizer 

 sections. This in eff'ect provided the use of 24 additional parameters for 

 shaping the loss in the pass band and resulted in an improved loss 

 chara(;teristic. 



