RADIO TELEPHONE SERVICE TO SHIPS AT SEA 



423 



tern consists of four separately shielded tuned circuits, coupled by small 

 capacities. The use of a screen-grid tube in the detector circuit 

 gives a two fold advantage over the use of a three-element tube in that a 

 higher input impedance is maintained at the higher frequencies and 

 the necessity for neutralizing against the reaction of the beating oscilla- 

 tor on the input circuit is eliminated. The beating voltage is made of 

 the order of 75 to 100 volts for the purpose of reducing the effective 

 tube noise in the detector plate circuit. With this arrangement no 

 d-c. plate voltage is ordinarily required. The screen voltage is 22 



Fig. 13 — Leviathan receiver. 



volts. The output circuit is tuned to the intermediate frequency of 

 300,000 cycles and connection with the first intermediate amplifier is 

 effected by means of a low impedance transmission line. The inter- 

 mediate frequency amplifier stages are coupled by means of doubled 

 tuned circuits. The use of properly designed circuits of this type 

 makes it possible to obtain a high degree of selectivity against unde- 

 sired frequencies while obtaining sufficient band width to maintain 

 ease of tuning and to pass the desired frequencies. The second de- 

 tector is of the conventional grid bias type. Automatic gain control 

 28 



