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BELL SYSTEM TECHNICAL JOURNAL 



bandwidth and the attenuation required at the beating oscillator fre- 

 quency. With two equations and two unknowns, the maximally-flat filter 

 theory was applied to the circuit shown schematically in Fig. 12.'' This 

 indicated that an output circuit bandwidth of 84 mc (to the three db 

 loss points), associated with two external resonant branches having band- 

 widths of 42 and 84 mc respectively, were needed to obtain a 20 mc flat 

 band with 30 db suppression of the beating oscillator. 



Such cavities were designed and attached to the output of a modulator 

 whose bandwidth had been adjusted by means of small resistive strips. 



MODULATOR 

 OUTPUT CIRCUIT 



3 4 



n FILTER ELEMENTS 



Fig. 12. — Sideband filter in waveguide. 



5 



(o I 



OL 



4040 4050 4060 4070 4080 



FREQUENCY IN MEGACYCLES PER SECOND 



Fig. 13. — Output circuit impedance match. 



The resulting impedance match gave a standing wave ratio of less than 

 one db over a 20 mc band (the plate circuit alone without the filter was 

 only about 5 mc wide to corresponding points) as shown in Fig. 13, and 

 the beating oscillator power at the output of the filter was less than one 

 tenth of a milliwatt, corresponding to TiZ db discrimination. 



The requirements and specifications for this particular experimental 

 model do not necessarily reflect out present thoughts upon the require- 

 ments for any particular microwave radio relay system; they are presented 

 here in some detail to indicate how certain specifications can be met, 

 rather than to express what those specifications should be. 



Other factors which influence the performance of the 416A modulator 



