THE RADAR RECEIVER 



715 



essentially equal to one, this factor also contributing to a narrowing of the 

 frequency regions of interest to those around the input, the beat oscillator, 

 and the output values. The third factor, which is of assistance to the con- 

 verter designer, is the effective separation of the input and output circuits 

 by the loss of the nonlinear element. Where a vacuum tube is employed as 

 the nonlinear element, the interaction of these circuits may be made quite 

 negligible and, in the case of the crystal rectifier the inherent loss of this 

 element, which may be of the order of 6 db and undesirable from a radar sys- 

 tem performance standpoint, does simplify the converter network design. 



It has been found in practice that it is sufficient to consider the impedance 

 conditions at the internal terminals of the converter networks in the fre- 

 quency regions which include /i,/i — fo^fi +/2 and 2/0 — /i. 



I-F 

 OUTPUT 



Fig. 10. — 1000-mc Vacuum Tube Radar Converter. .Simplified schematic diagram. 



The matter of etficient transfer of power from the local beating oscillator 

 to the nonlinear element is of secondary importance generally because of the 

 relatively large amount of power available. This condition is advantageous 

 allowing mismatch loss in this branch to effectively minimize the unwanted 

 interaction effects with input and output circuits. 



Figure 10 illustrates the schematic and certain constructional features of 

 a vacuum-tube converter which has an operating frequency of approxi- 

 mately 1000 mc. The similarity of circuit and mechanical arrangement to 

 that of the radio-frequency amplifier unit, shown in Fig. 7, is apparent. 

 In the case of the GL-2C40 converter the two input frequencies are similarly 

 probe coupled to the grid-cathode circuit, maintaining optimum impedance 

 conditions for the signal input and locating the beat oscillator probe so as 



