PROPAGATION STUDIES AT MICUOWAVE FHIOQUENCIKS 



93 



RECEIVING EQUIPMENT 



The ret'oi\-ing antenna, a large horn, was mounted between two poles 

 guyed for support. It had an apertiu'e of about 90 square feet and a gain 

 of approximately 38 db over a dipole. The recei\'er circuit is sliown in Fig. 

 2. About GO db of gain at 4000 mc was provided by either two or three 

 stages of t raveling- wa^■e tube amplifier depending upon the gain of the 

 particular tubes used. It was necessary to provide very good shielding 

 and also careful filtering of all power leads to eliminate the tendency for 

 this amplifier to sing. The amplifier fed two crystal detectors through a 

 hybrid tee junction. Each detector employed a silicon crystal of the 

 IN23B type. 



Two incUcator circuits are shown in Fig. 2. These circuits are very 

 similar except that one employed a vertical amplifier coupled to a Dumont 

 5XP2 CRO tube, whereas in the second the baseband output of the 

 crystal was fed dii'ectly onto the deflection system of a tra^•eling-wave 

 type of CRO tube. The latter CRO tube, which has been described by 

 J. R. Pierce in the November, 1949, issue of Electronics, has a very high 

 deflection sensitivity and is used with a microscope to enlarge its trace; 

 hence, no amplification was required between it and its driving crystal. 

 The deflection system of this tube has a bandwidth of 500 to 1000 mc. 

 The micro-oscilloscope was provided primarily for photographing pulses 

 by means of a 35-mm camera attached to the microscope. (Exposure 

 time was 5 to 15 seconds. The time recorded for each picture corresponds 



4000 MC 

 PULSES 



WAVEGUIDE 



HYBRID 

 JUNCTION 



\ C 



TRAVELING 



WAVE 

 AMPLIFIERS 



BASE-BAND 

 PULSES 



INDICATOR NO. 1 



CRYSTAL 

 DETECTOR 



: TERMINATION 



NARROW-BAND 

 CRYSTAL AMPLIFIER 



DETECTOR 



Fig. 2 — Receiving equipment. 



