COMMON FREQUENCY BROADCASTING 



585 



were about one part in a hundred million. It is relatively insensitive 

 to changes in filament current, though this is maintained constant 

 within narrow limits by a ballast lamp. Since a change of one per cent 



Fig. 5 — A corner of the operating room at station WOC. 



in the plate voltage causes an immediate change in the frequency of 

 about one part in fifteen million and an ultimate change of about one 

 part in two million, the crystal oscillator is now being operated from 

 batteries. 



