COMMON FREQUENCY BROADCASTING 



583 



equipment before the door can be opened. It was a simple matter to 

 install one of these compact self-contained units adjacent to each trans- 

 mitter to replace the existing crystal control equipment as the source 

 of the carrier frequency. A corner of the operating room at station 

 woe is shown in Fig. 5, with a part of the radio transmitter at the ex- 

 treme right and the oscillator-amplifier mounted adjacent to it. The 

 author is holding the crystal oscillator and constant temperature oven, 

 and over his head to the left is the loud speaker through which the pro- 

 gram from the monitoring point is received. 



Fig. 3 — Front view of crystal controlled oscillator-amplifier unit. 



The extraordinary frequency stability of these units has not been 

 obtained through any radical change in design but has come rather as a 

 result of the refinement of all the component elements to form a 

 coordinated unit. A clamped crystal has been used in an improved 

 type of holder, designed to maintain a constant pressure on the crystal 



