655 



HYDROGRAPHIC MANUAL 



Page 612 



01 25 MA 



Thermo-couple type 



LEAD TO BUOY TRANSMITTER 



Figure 136.— Sono-radio buoy dummy tuning antenna. 



water. The dummy antenna circuit is shown in figure 136. When this is used for 

 tuning a sono-radio buoy, the antenna is disconnected and the dummy antemia con- 

 nected in its place. 



Numerous methods may be used to ndicate when the antenna and radio-frequency 



circuits are properly tuned. The 

 antenna lead can be opened near the 

 anteima coupler and a thermocoupled 

 type of radio-frequency ammeter 

 inserted. It should have a range of 

 to 250 milliamperes or more, de- 

 pending on the power used. A 

 second and better method is to 

 couple a low energy-absorbing circuit 

 loosely to the antenna and to tune 

 the radio-frequency circuits' by not- 

 ing the reading on an indicating 

 meter. The energy-absorbing cir- 

 cuit may consist of a coil of two turns 

 of wire about 3 inches in diameter, 

 connected to a rectifier-type volt- 

 meter. A second circuit that is very satisfactory consists of a short antenna connected 

 to a vacuimi-tube voltmeter, the antenna being loosely coupled to the antenna of the 

 sono-radio buoy. 



When tuning the antenna, the radio transmitter is usually operated at reduced 

 power by closing a key for this specific purpose. The condenser of the antenna-coupling 

 circuit is tuned by removing the threaded plug in the antenna-coupling housing and 

 inserting a screwdriver in the slotted end of the condenser shaft. The best results are 

 obtained when this condenser is adjusted so that the reading on the tuning indicator 

 device is a little below peak value when the condenser is on the minimum capacity side 

 of peak tunmg. 



655. Operating Difficulties 



Abnormal performance of a sono-radio buoy is usually disclosed in one of two 

 ways — either it is too insensitive to distant bombs, or there is an excess of stray signals. 

 A subnormal range of a sono-radio buoy may be caused by: 



(a) The sono-radio buoy is located at a place where the bomb sounds are not reaching the 

 hydrophone. 



(b) Insufficient audio-amplifier gain. The gain may have been improperly adjusted originally 

 or may have changed because of deteriorated, parts. 



(c) Faulty hydrophone. Either the electroacoustic unit is defective or water is leaki,,p into the 

 hydrophone housing or electric cable. 



(d) Weak radio signals may result from defective transmitting equipment, improper tuning, 

 damaged antenna, or water leaking into the drum or antenna-coupling housing. They may also result 

 from poor radio transmission conditions. 



An excess of strays may result from the following: 



(e) The audio-amplifier gain may be excessive, owing to improper gain adjustment, regeneration 

 of the amplifier caused by improper design or construction, or decrease of C battery bias voltage. 



(/) Defective parts may cause electric noises in the amplifier. 



(g) Salt water leaking into the drum will sometimes cause the electric equipment to operate, 

 producing excessive strays, as a preliminary to final cessation of operation. 



