226 BELL SYSTEM TECHNICAL JOURNAL 



adjustment is provided by the input tuner shown. With it, the reflection 

 coefficient may be reduced to zero at the desired channel band center, and 

 when this is done the standing wave ratio at the input is less than 2 db over 

 a 20-megacycle band. 



The bandwidth of the converter is largely determined by the IF trans- 

 formers shown which transform the balanced output impedance to the 

 unbalanced 75-ohm coaxial line connecting to the IF amplifier. When 

 transformers having a coupling coefficient of about 0.5 are used, transmis- 

 sion variations of less than 0.1 db over a 20-megacycle band are obtained. 



Fig. V-5. — Receiving converter with low noise IF preamplifier. 



The noise figure of the repeater amplifier is determined by the conversion 

 loss and noise figure of the converter and the noise figure of the IF ampli- 

 fier.'* The converter designed for the New York-Boston circuit has a 

 conversion loss of about 5f db and its noise figure is 10 db. Thus when it 

 is used with an IF amplifier having a noise figure of 7 db, a figure of 14 db 

 is obtained for the over-all noise figure of the n peater amplifier. Figure 

 V-5 shows this converter with a low noise preamplifier attached.* 



I.F. AMPLIFIERf 



Most of the gain of the IF amplifier is obtained with stages using double 



tuned, symmetrically loaded (or 'matched") interstage transformers, de- 



" Loc. cit. 



* Developed by H. C. Foreman and B. C. Bellows, Jr. 



t This section prepared by Karl G. Jansky who, together with V. C. Rideout, did the 

 work on IF ampUfiers. 



