THE DESIGN OF TETRODE TRANSISTOE AMPLIFIERS 



835 



^ below, the bandwidth at which the response is down a given number of 

 db can also be computed. 



From Table II one observes that this design provides a gain of about 

 18 db with half power frequencies where the susceptance B2 has changed 

 by ±3/i22r mhos from its value of — 2/i22r at the center of the pass band. 

 The value of h22i corresponds to approximately 1 fifxi of capacitance and 

 if the stray capacitance amounts to 3.5 nni, then the bandwidth is 

 AB2/2C since the slope of the susceptance of a tuned circuit is 



I . 



2C- 



m 



hos 



rad/sec 



I Thus the bandwidth is approximately 



I 



6 -3.5 -10"' 



I 2 -2.5 -10-12.6.28 



(ir 3.7 mc. This is the actual value of load capacitance measured on an 

 experimental amplifier with a vacuum tube voltmeter connected to the 

 output. The measured response of this amplifier with a load of Yl = 

 (08 - j215) • lO"*^ at 30 mc (Gl = 2/?22r) shows a peak gain of 18.3 db and 



I half power points separated by 3.8 mc. For a given value of Gl , the 

 bandwidth of the amplifier will varj^ inversely with the total capacitance 

 in the output circuit. The same gain as obtained in the sample given 

 above, can be obtained over a narrower band by increasing the load 

 capacitance. Since the minimum capacitance is fixed, if one wishes to 

 increase the width of the pass band, a higher value of G2 must be used. 



;In the same manner as is used to arrive at the data shown on Table II, 

 Table III is computed for a value of G2 = 6/?22r (Gl = 5/?22r). 



In this case, the maximum value of Po/Pi occurs when B2 = — 3/i22r • 

 Ihe source impedance is selected to be 75 — j45 ohms at 30 mc and the 

 jcmainder of the table is computed. The maximum computed gain is 

 approximately 16 db with half power frequencies where the susceptance 



Table III 



B2 



Evaluation of Transducer Gain of I.F. 

 Amplifier 



P./Pi 



/„. 



/',,,/Power avail- 

 able from source 

 Transducer gain. . 

 < iain db 



21 



83 + j20 



0.97 



20 



13.0 



