HIGH ACCURACY HETERODYNE' OSCILLATORS 



417 



The frequency setting is recorded on a 300-inch film scale such as 

 described above. This gives a spread of two inches per kilocycle. 

 With the 50-cycle divisions marked directly the mechanism can be 

 readily set to an accuracy better than 25 cycles. The visibility of the 

 scale is greatly enhanced by a pilot lamp placed in back of the scale 



Fig. 4 — Front view of the oscillator. 



window with an intervening opal glass. A crank on the front of the 

 panel is used to set the oscillator, the range being covered in 47 revolu- 

 tions. When changing the frequency setting even at a moderate rate 

 the speed with which the film moves prevents the operator from observ- 

 ing the frequency setting. To make the adjustment more convenient, 

 a coarse scale is recorded on a dial which can be read easily to one 



