86 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1956 



tions from the two side arms so that when conditions in the two arms 

 are identical there is no output. The crystal diodes coupled to the side 

 arms are equivalent to those shunted across the two lines of Fig. 15A. 



Fig. 18, which is a plot of the measured input-output characteristic 

 of the regenerator used in the loop test, shows how the device acts as a 

 combined sheer and retimer. Curve A, ol)tained with equal biases on the 

 two diodes, is the characteristic with no gating pulse applied i.e. the 

 diodes are normally biased in this manner. It is seen that this condition 

 produces the maximum of loss through the device. By shifting one diode 

 bias so as to produce a differential of 0.5 volt the characteristic changes 

 to that of Curve B. This differential bias can be supplied by the timing 

 pulse in such a way that this pulse shifts the characteristic from that 

 shown at A to that shown at B thus decreasing the loss through the de- 

 vice by some 12 to 15 db during the time the pulse is present. In this way 

 the regenerator is made to act as a gate — though not an ideal one. 



We see from curve B that with the differential bias the device has the 

 characteristic of a slicer — though again not ideal. For lower levels of 

 input there is a region over which the input-output characteristic is 

 square law with a one db change of input producing a two db change of 

 output. This region is followed by another in which limiting is fairly 

 pronounced. At the 8-db input level, which is the point at which limiting 

 sets in, the loss through the regenerator was measured to be approxi- 

 mately 12 db. The characteristic shown was found to be reproducible 

 both in these experiments at 4 kmc and in those bj'- A. F. Dietrich at 

 11 kmc. 



For a perfect slicer only an infinitesimal change of input level is re- 



GATING 

 PULSE 



■AAV-i_ 



ARM 2 



RF 



OUTPUT 



Fig, 17 — Microwave regenerator employing a single hybrid junction. 



