. The Bell System technical journal . d as power ratios. A rigorous definition ofreceiver noise figure has been given l)v H. T. Friis Noise Figures of Radio Receivers,Proc. L R. E., vol. 32, pp. 419-422; July, 1944. * C. F. Edwards, Microwave Converters, presented orally at the Winter TechnicalMeeting of the /. R. E., January 1946 and submitted to the /. R. E. for publication. SILICON CRYSTAL RECTIFIERS 19 with poorer noise figures, the drive for optimum performance is higherthan the figures cited above. Conversely, for intermediate frequencyamphfiers with exceptionally low noise figures, opti
. The Bell System technical journal . d as power ratios. A rigorous definition ofreceiver noise figure has been given l)v H. T. Friis Noise Figures of Radio Receivers,Proc. L R. E., vol. 32, pp. 419-422; July, 1944. * C. F. Edwards, Microwave Converters, presented orally at the Winter TechnicalMeeting of the /. R. E., January 1946 and submitted to the /. R. E. for publication. SILICON CRYSTAL RECTIFIERS 19 with poorer noise figures, the drive for optimum performance is higherthan the figures cited above. Conversely, for intermediate frequencyamphfiers with exceptionally low noise figures, optimum [performance isobtained with lower values of beating oscillator drive. If desired, somewhathigher currents than milliamperes may be employed without damageto the crystal. The impedance at the terminals of a converter using crystal rectifiers,both at radio and intermediate frequencies, is a function not only of therectifier unit, but also of the circuit in which the unit is used and of the SILICONRECTIFIER BY PASSCONDENSER y^^. SIGNALINPUT Fig. 9—Schematic diagram of crystal converter. power level at which it is operated. Consequently the specification of animpedance for a crystal rectifier is of significance only in terms of the circuitin which it is measured. Since the converters used in the production testingof crystal rectifiers are not necessarily the same as those used in the field,and since in addition there are frequently several converter designs forthe same type of unit, a specification of cr>stal rectifier impedance in pro-duction testing can do little more than select units which have the sameimpedance characteristic in the production test converter. The impedancesat the terminals of two converters of different design but using the samecrystal rectifier may vary by a factor of 3 or even more, with the inter-mediate frequency impedance generally varying more drastically than theradio frequency impedance. The variation is also a function of the con- 20 BEL
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