SILICON CRYSTAL RECTIFIERS 



19 



with poorer noise figures, the drive for optimum performance is higher 

 than the figures cited above. Conversely, for intermediate frequency 

 amphfiers with exceptionally low noise figures, optimum [performance is 

 obtained with lower values of beating oscillator drive. If desired, somewhat 

 higher currents than 2.0 milliamperes may be employed without damage 

 to 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 the 

 rectifier unit, but also of the circuit in which the unit is used and of the 



SILICON 

 RECTIFIER 



BY PASS 

 CONDENSER 



y^^ 



SIGNAL 

 INPUT 



Fig. 9 — Schematic diagram of crystal converter. 



power level at which it is operated. Consequently the specification of an 

 impedance for a crystal rectifier is of significance only in terms of the circuit 

 in which it is measured. Since the converters used in the production testing 

 of crystal rectifiers are not necessarily the same as those used in the field, 

 and since in addition there are frequently several converter designs for 

 the 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 same 

 impedance characteristic in the production test converter. The impedances 

 at the terminals of two converters of different design but using the same 

 crystal rectifier may vary by a factor of 3 or even more, with the inter- 

 mediate frequency impedance generally varying more drastically than the 

 radio frequency impedance. The variation is also a function of the con- 



