Page 605 



RADIO ACOUSTIC RANGING 



6521 



stuffing boxes in the flanged top of the drum. The batteries are contained in a wooden 

 frame which is secured in the bottom of the drum. 



The Dorsey hydrophone is used with this sono-radio buoy. This hydrophone and 

 the method of supporting it are described in 6561 and 6562. The hydrophone is 

 coupled to the first tube of the audio amphfier by means of a hne-to-grid transformer, 

 selected to match the impedance of the hydrophone used. 



6521. Audio Amplifier 



The audio amplifier consists of two stages; the first stage employs a type 32 screen-grid tube 

 acting as a voltage amplifier, which is impedance-coupled to the second tube by means of an induc- 

 tance-capacitance-resistance combination. The second tube is a high mu duplex-diode triode of which 

 only the triode part is used. The plate circuit of this tube is coupled to the keying circuit by means 

 of a 1:3 transformer. A step-by-step gain-control attenuator forms part of the coupling circuit 

 between the first and second tube, arranged so that the amplifier sensitivity may be changed by 

 intervals of 2 decibels. The full range of this attenuator is 20 decibels, permitting variations of gain 

 from 65 decibels to the amplifier's maximum gain of approximately 85 decibels. No attempt is made 

 to tune the amplifier, but the characteristics of the inductance and capacitance parts of the circuit are 

 such that frequencies below 1000 cycles are favored. 



OOZ^f 



5308 Z Parallel 

 4FiH 



Z Parallel SI 56 

 20 FZ 



Figure 134.— Circuit diagram of East Coast sono-radio buoy. 



6522. Keying Circuits 



A type 30 tube acts as the keying device to operate the radio transmitter. This tube is biased 

 to beyond cutoff so that when there is no bomb signal there is no conduction through the tube, and 

 the radio transmitter cannot operate. When a bomb signal actuates the keying tube, current flows 

 through the tube and makes the screen of the radio-frequency oscillator positive, and oscillations 

 commence almost instantly. This type of circuit requires a connection between the filament of the 

 keying tube and the screen grid of the oscillator, therefore the keying tube must have separate fila- 

 ment and bias batteries which are well insulated above ground. 



Associated with the keying circuit are two other circuits, one for shortening the radio signal 

 regardless of the length of the bomb signal, and a second circuit to silence the sono-radio buoy for a 

 period of a few seconds after the radio signal has been transmitted. The signal-shortening circuit is 



