2614 HYDROGRAPHIC MANUAL Page 150 



The survey ship, or a launch, should anchor at the approxunate position of the 

 hydrophone. The tested cable, wound on a reel with the heavy-duty cable on top, is 

 placed in a whaleboat or motor sailer so that it may be readily unreeled. The small 

 boat with the cable proceeds to the beach, or to a safe anchorage just offshore from the 

 breakers from where the cable is hauled ashore by a heaving line. Heavy surf or a 

 wide stretch of breakers may necessitate the use of a Lyle gun to shoot the line ashore, 

 or the laying may have to be postponed until sea conditions are more favorable. After 

 the end of the cable has been pulled ashore and secured, the small boat heads toward 

 the anchored ship, paying out the cable. Wlien the ship is reached, the end of the 

 cable is passed aboard where it is spliced to the hydrophone, and the anchoring assembly 

 as described in 2612 is attached. The hydrophone anchor is first lowered by a trip 

 line, followed by the buoy anchor which is anchored as far from the hydrophone anchor 

 as the wire rope connecting them will permit. 



2614. Electric Equipment 



The electric circuits of the amplifier and transmitter may be identical with the sono- 

 radio buoy circuits (see section 65), except that 6-volt transmitting tubes are used 

 because they are more reliable and there is not the same need to conserve power. And a 

 separate bomb-listening circuit may be incorporated in the amplifier. There are numer- 

 ous advantages to be gained from the latter. Some of these are: the gain of the listening 

 circuit may be controlled independently from the main amplifier, interaction between 

 the listening circuit and the main amplifier is reduced, and spurious noises caused by 

 the operation of the keying circuit and radio transmitter are eliminated from the listen- 

 ing circuit. 



Another useful arrangement is to connect the radio transmitter to the amplifier 

 so that the circuit may be kept open at all times except while held closed manually, 

 as by a push button in the circuit. The push button can be pressed a few seconds 

 before the expected arrival of a bomb signal, the time being judged from the approx- 

 imate distance of the ship from the hydrophone. In this way the radio transmitter 

 is kept inoperative until just before the arrival of the bomb signal, thus reducing the 

 likelihood of its being operated by water noises. 



Where the shore station is at some distance from the inshore end of the hydrophone 

 cable, a two-stage amplifying booster is usually inserted about midway between the 

 hydrophone and the station equipment. The booster is contained in a waterproof 

 box, located well inshore from the high-water line at a protected place. It may contain 

 its own power supply or be supplied with power from the shore station. The inshore 

 end of the hydrophone cable is connected to the booster, a land line extending from 

 there to the shore station. The gain of the booster amplifier is fixed and any necessary 

 change in gain is made at the shore station amplifier. 



The electric equipment is battery operated, because an a-c power supply is rarely 

 available where shore stations are needed. A portable gasoline-driven generator is 

 needed for charging the batteries. 



2615. Antenna 



The antenna may be erected between two trees from which the interfering branches 

 have been removed. If trees are not available it is generally necessary to erect two 

 well-guyed masts at a suitable distance apart. The axis of the antenna should be 

 approximately at right angles to the area to be surveyed. 



