70 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1956 



HYBRID 



JUNCTION 



' NO. 3 



CW 



OSCILLATOR 



(4 KMC) 



TRAVELING WAVE 



AMPLIFIER 



(NOISE GENERATOR) 



Fig. 2 — The circulating loop. 



To provide RF test pulses for this loop the output of a 4 kmc, cw 

 oscillator is gated by baseband pulse groups in a microwave gate or 

 modulator. The resultant microwa\-e pulses are fed into the loop (heavy 

 line) through hybrid junction No. 1. They are then amplified by a trav- 

 eling-wave amplifier the output of which is coupled to the pulse regen- 

 erator through another hybrid junction (No. 2). The purpose of this 

 hybrid is to provide a position for monitoring the input to the regen- 

 erator. A monitoring position at the output of the regenerator is pro- 

 vided by a third hybrid, the main output of which feeds a considerable 

 length of waveguide which provides the necessary loop delay. At the far 

 end of the waveguide another hybrid (No. 4) makes it possible to feed 

 noise, which is derived from a traveling-wave amplifier, into the loop. 

 The combined output after passing through a band pass filter is ampli- 



