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BELL SYSTEM TECHNICAL JOURNAL 



ment is located at the high-impedance end of this transmission line, while 

 the other end is essentially short-circuited at the input frequency by means 

 ot a small by-pass condenser element built into the IF output transmission 

 line. The input line is couf)led into this tuned circuit by means of a variable 

 coupling probe and the local beat oscillator in turn is similarly coupled to 

 the input line. The point of coupling of the beat frequency oscillator input 

 is so arranged as to introduce an effective mismatch and thus provide ade- 

 quate isolation of this and the input circuit. The output circuit of this con- 

 verter includes the by-pass condenser previously referred to, together with 

 the input transformer of the tirst IF amplitier stage. The average loss of a 



BY- PASS 

 CONDENSER 



BEATING- 

 5) OSCILLATOR 

 INPUT 



SIGNAL 

 INPUT 



Fig. 13. — 3000-mc Crystal Converter. Schematic diagram. 



3000-mc crystal converter of this type was 6 db and a noise figure of 11 db 

 was realized. 



Another design of crystal converter which was developed during the early 

 part of the war, and whose basic form was employed in many military radar 

 equii)ments operating in the region of 1(),(K)() mc, is shown in Fig. 14. Here 

 the silicon crystal cartridge is positioned within the waveguide with its axis 

 parallel to the E vector plane and at a point approximately one-cjuarter of a 

 wavelength from the short circuiting j)iston which terminates this assembly. 

 The II'' output is obtained from the coaxial line mounting structure shown 

 which offers a low impedance to the injjut frequency by virtue of its equiva- 

 lence to a one-half wavelength element with a short circuit at the far end. 



