83-4 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1956 



■Pi. 



Fig. 16 — Typical input circuit. 



read from the charts. From the source-load arrangement shown in Fig. 

 16, one readily computes 



I ^-' s I •'^tin 

 Pi '^ ^ 



{R. + RinY + (X. + XinY 



Power Available from Source 



Es 



4:Rs 

 'iihsJttin 



(32) 



(Rs + RinY + (Xs + XinY 



The source impedance selected for the amplifier is 75 — j87 ohms at 30 

 mc. The 75 ohms is selected to reduce the effect of variations in input [ 

 impedance when it is reduced further by the internal feedback. The 87 

 ohms of capacitive reactance is selected to tune the input reactance at f 

 the peak of response. Using Fig. 8 with the overlay of Fig. 9(a) along 

 with (32) under the assumption that Xs varies insignificantly over the 

 frequencies involved one obtains Table II. This table shows the varia- 

 tion of transducer gain as the value of B2 is changed as well as indicating 

 the value of B2 required for the maximum gain. Thus, if the total output 

 capacitance is known, the load admittance required to give the maxi- 

 mum gain at the desired frequency can be computed. As Avill be shown 



Table II — Evaluation of Transducer Gain of I-F 



Amplifier 



Po/Pi 



^in 



P,/Power avail- 

 able from 



source 



Transducer gain 

 Gain, db 



—ShiiT 



50 



22 + ;48 



0.61 



30 



14.8 



-4/»2 



64 



23 -j- yss 



0.66 



42 



16.2 



-ihi 



73 



28 + i73 



0.78 



57 



17.5 



-2/j!2r 



75 



36 -F i87 



0.87 



66 



18.2 



—hi^T 



59 



67 + ;99 



0.98 



58 



17.6 



Ohiir 



50 



96 + jU 



0.98 



49 



16.9 



hiiT 



00 



120 + j67 



0.94 



36 



15.5 



