742 BELL SYSTFAT TECIIXICAL JOURNAL 



stage band width and the o\-cr-all band width of a multistage ami)lifier 

 employing double-tuned interstage circuits is given by 



B = A/^V4(2'/^ - 1) 



which is illustrated in Table II togetlier with the corresponding over-all gain 

 of multistage IF amplifiers of this design. 



The third type of interstage network arrangement illustrated in Fig. 27 

 represents a method employed to realize improved performance of the single- 

 tuned interstage network type by resonating alternate interstages at fre- 

 quencies above and below the desired midband IF value. This stagger-tuned 

 interstage design permits greater gain per stage together with an increased 

 over-all band width for each pair of amplilier stages over that obtained with 

 the synchronous single-tuned design. In the case of IF amplifiers having 

 six or more stages a variation of this stagger-tuned method can be employed 

 where three successive interstages are considered as a design unit and the 

 individual interstage resonances are adjusted below, above, and centered at 

 the midband IF respectively. To afiford a measure of the improved perform- 

 ance of a stagger-tuned IF amplifier we may consider the relative performance 

 of a 6-stage IF amplifier of 5 mc over-all band width employing the 6AK5 

 vacuum tube. An individual interstage band w'idth of 7.2 mc and an over- 

 all gain of 116 db will result from the use of stagger-tuned interstage circuits 

 while reference to Table II indicates the synchronous single-tuned design 

 would have an over-all gain of only 80 db while the double-tuned design 

 would result in an over-all gain of 125 db. The use of a triple stagger-tuned 

 design would produce a 6-stage amplifier having approximately the same 

 gain performance as the double-tuned example above. 



The choice of the interstage network configuration to be employed in a 

 radar IF amplifier must be made considering the circuit efiiciency, the gain- 

 frequency stability behavior, and with due regard for the ever-present prob- 

 lem of maintenance of performance under the field conditions of modern 

 warfare. From a standpoint of circuit ellhciency alone, it has been shown 

 that the synchronous single-tuned interstage network is decidedly inferior 

 to the more complex forms, but the obvious simplicity of construction of this 

 type and the possibility of adjustment and realignment with simple methods 

 available in the field is a strong recommendation for its adoi)tion in military 

 radar IF ampliliers. The double-tuned circuit has a considerable advantage 

 in circuit performance over the case above, but some portion of this increased 

 elTiciency must be sacrificed since it is impractical to construct this network 

 with adjustable elements. Here the normal variations in interstage capaci- 

 tance with replacement of vacuum tubes or aging effects must not be allowed 

 to reduce the over-all amplifier performance below the design limit. The 

 solution to this problem must be achieved by design of each interstage circuit 



