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BELL SYSTEM TECHNICAL JOURNAL 



echoes, the hangover or release times should be constant for various 

 applied voltages. In the vodas, the change in release time over a 

 wide range of inputs is less than 1 per cent. Adjustments are made by 

 varying the condensers and resistances of the auxiliary circuits shown 

 in Fig. 3. Typical values obtained by this method are indicated in 

 Fig. 11. 



V) 120 



80 



? 60 



40 



< 20 



0.4 0.8 1.2 1.6 2.0 2.4 2.8 



RELEASE CIRCUIT CAPACITY IN MICROFARADS 



Fig. 11 — Release time vs. capacitance. 



The vodas amplifier-detectors have broadly tuned input circuits to 

 exclude by frequency discrimination many of the frequencies induced 

 by power sources and those which are unnecessary for speech opera- 

 tion. The sensitivity- frequency characteristic is shown on Fig. 12. 



400 



800 1200 1600 2000 

 FREQUENCY IN CYCLES PER SECOND 



2400 



2800 



Fig. 12 — Sensitivity -frequency characteristics of the vodas. 



