Page 597 radio acoustic ranging 6431 



is described in 284. The electric circuits of the several types of sono-radio buoys are 

 very similar in many respects, and the distance performance is about the same for all 

 of them. Two of the types in most general use are described in 651 and 652, and their 

 features are compared in 653. 



The principal parts of the electric equipment of a sono-radio buoy are the audio 

 amplifier, the keying circuit, and the radio transmitter. The primary purpose of the 

 audio amplifier is to amplify the small voltage, created across the terminals of the 

 hydrophone by the bomb signal, sufficiently to operate the keying circuit. The keying 

 circuit then sets the radio transmitter into operation. The general requirements of 

 these three component parts are described in 6431, 6432, and 6433. 



6431, Audio Amplifier 



The gain of the audio system must be sufficient to provide the required sensitivity— 

 experi(mce has indicated that a gain of 80 to 90 decibels is more than ample, and much 

 less than this is used in practice. The values are for measurements between the input 

 of the hydrophone and the keying circuit. The gain needed in the amplifier depends 

 somewhat on the sensitivity of the hydrophone used, and the amount of gain that can 

 be used is limited by the unwanted noises entering by way of the hydrophone. Conse- 

 quently the latter also limits the distance range of the sono-radio buoy. Means should 

 therefore be taken to reduce spurious noises to a minimum and thereby increase the 

 bomb-to-noise ratio — proper suspension of the hydrophone, as described in 656, will 

 aid in this respect. 



The gain of the amplifier must be maintained at a nearly constant value while the 

 sono-radio buoy is on station. Tests have proved that the gain can be maintained 

 within 2 decibels of the original value for at least 1 month of operation. Tubes should 

 be used that retain fairly constant operating characteristics with reasonable changes of 

 voltage. Voltage and current regulators may be used to good advantage in maintaining 

 the gain of the amplifier at a constant value. The circuits of the sono-radio buoA^s 

 are arranged so that the decay of the B and C batteries has a compensating eft'ect on 

 the amplifier gain, with almost no net change. 



Within limits, amplitude and frequency distortion may be disregarded in the design 

 of the amplifier. It is not necessary to have the gain of the amplifier flat in frequency 

 nor is it necessary to amplify frequencies much above 300 cycles. In fact, in some cases 

 it has been found advantageous to have the amplifier peaked for a certain frequency 

 range. To conserve the B batteries, the amplifier tubes should be biased close to the 

 cut-oft" point. This will naturally result in amplitude distortion, but this can be toler- 

 ated in R.A.R., since it is not necessary to reproduce and transmit the characteristics of 

 the bomb sound with fidelity — the essential requirement is that thej^r.s-^ bomb signal 

 actuates the radio transmitter immediately on arrival at the hydrophone. 



One of the primary requirements of the amplifier is that it be stable. Tendencies 

 toward regeneration or degeneration cannot be tolerated because unpredictable opera- 

 tion would be introduced, and dift'erent results would be obtained from dift'erent sono- 

 radio buoys of the same type; and, in addition, a variable time lag would be introduced 

 to lessen the accuracy of R.A.R. distance measurements. Time lag is inherent in all 

 audio-frequency amplifiers to varying degrees, but the component parts of the amplifier 

 must be selected and arranged in such a manner that this lag will be small and relatively 

 constant. 



