TD-2 MICROWAVE RADIO RELAY SYSTEM 



1061 



amplifier output is applied to the repeller of a deviation oscillator described 

 below. 



A microwave heterodyne method of generating a 70-megacycle FM signal 

 was selected because it was found possible to design a highly linear deviator 

 in the microwave region. It also allows separate tests to be made of the 

 transmitter and receiver linearity and thus facilitates maintenance, 



A reflex klystron oscillator may be frequency-modulated by superim- 

 posing a modulating signal on the repeller d-c voltage. The rate of frequency 

 change with change of repeller voltage passes through a minimum near the 



BASEBAND 

 INPUT 



Wv 



VIDEO 

 AMPLI 

 FtER 



LINEARITY ADJUSTMENTS 



^'ggS;iTr.^i-# To qTd ] 



Fig." 16— Block diagram of FM terminal transmitter. 



point of maximum power output. At a deviation of =t4 megacycles, the 

 difference in FM sensitivity over the 8-megacycle swing would normally be 

 sufficient to produce intolerable distortion. However, the operating fre- 

 quency of a reflex oscillator is subject to modification by the load impedance 

 seen by the oscillator. This effect is commonly called "pulling." In the de- 

 viation oscillator, this effect is made use of to provide deviation linearity 

 over a range of more than 10 megacycles. The load circuit for the 4280- 

 megacycle deviation oscillator consists of a variable attentuator, a short 

 length of line, and a variable position short circuit. Adjustments of these 

 two variables allows complete control of the reactance seen at the output 



