1056 THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1951 



described above. The three stages are connected together in cascade through 

 waveguide spacers and reactance tuners of such dimensions that the joining 

 of each output cavity with the following input cavity (or filter section in the 

 case of the output stage) forms a double-tuned critically coupled transformer. 

 A flat over-all transmission characteristic is thereby obtained which is about 

 20 megacycles wide between points 0.1 db down. While capable of greater 

 gain, the amphfier is adjusted to a gain of 18 db at an output power level of 

 0.5 watt. A double directional coupler in the waveguide between the trans- 

 mitting amplifier and the transmitter channel separation filter provides 

 monitoring and output alarm signals. 



Fig. 13— Transmitter amplifier. 



E. Microwave Sources and Control Circuits 



The receiver control unit may be seen in Fig. 8. It contains a stabilized 

 d-c amplifier for IF automatic gain control and level adjustments, and test- 

 ing facihties for checking the performance of the receiver. The control unit 

 also contains power controls and protection devices for the plate and fila- 

 ment circuits. The transmitter control unit contains controls for the applica- 

 tion of power and bias to the transmitter and a means for metering various 

 circuits. 



The microwave generator, which furnishes about 200 milliwatts of beating 

 oscillator power for the transmitter and receiver, is a stable microwave 

 frequency source developed by harmonic generation from a quartz crystal 

 in the vicinity of 18 megacycles. The multiplication takes place in six har- 



