6523 HYDROGRAPHIC MANUAL PaGE 606 



composed of a relay in series with the plate-supply lead of the oscillator, so that when a bomb signal 

 is received the oscillator tube draws plate current and the relay is operated, the contacts of which 

 short the grid of the keying tube to the filament through a 1-microfarad condenser, thus stopping 

 the operation of the keying tube and hence the oscillator. The length of the radio signal is only 

 about 0.12 second. The silencing circuit consists of a 1-megohm 4-microfarad resistance-capacitance 

 arrangement in the plate circuit of the keying tube. The condenser is normally charged to the same 

 voltage as the B battery, but when the bomb signal is received the condenser discharges into the 

 keying tube. A period of a few seconds is required to recharge this condenser through the l-megohm 

 resistor and during this period the sono-radio buoy is inactive. Not all types of East Coast sono- 

 radio buoys employ the signal-shortening-and-silencing circuits for reasons discussed in 6432. 



6523. Radio Transmitter 



The radio-frequency power is generated by a type 33 power pentode, arranged in a conventional 

 crystal-controlled oscillator circuit. The transmitter frequency normally used with this sono-radio 

 buoy is either 4135 or 4160 kilocycles. The crystal is described in 6513. The power output of the 

 transmitter is about 3 watts. The antenna transmission line is a two-conductor rubber-covered Tyrex 

 cable about 4 feet long which is link-coupled to both the oscillator circuit and the antenna coil. The 

 housing for the antenna-matching circuit is a cast brass cylinder open at only one end onto which a 

 cap screws. All the electric circuits are attached to this screw-on cap, and the two stuffing boxes 

 for the antenna lead and the transmission line pass through it. It also contains a threaded hole 

 through which the antenna tuning condenser can be adjusted, which is normally closed by a standard 

 )4-inch pipe plug. 



The antenna is 18 feet long, made of hard-drawn copper tubing with a ^i-inch outside diameter. 

 The antenna is supported along the narrow edge of the centerpole of the buoy structure, and insulated 

 from it at 2^4-foot intervals by means of insulators of the house bracket type. 



The controls mentioned in 652 that can be reached through the handhole in the lid of the drum 

 are to permit adjusting and testing the circuits without opening the drum. There are four controls 

 and two metering jacks grouped under the handhole opening. Two of the controls operate selector 

 switches, the third is a push button, and the fourth is a rheostat control. One of the selector switches 

 is a 3-gang 11-position nonshorting type of switch. Its functions are to control the amplifier gain 

 by steps, to measure the filament, grid, and plate voltages of all tubes, and to turn on the radio 

 transmitter for tuning and testing purposes. Only the gain control part of this switch is shown in 

 figure 134. A suitable meter is plugged into the metering jacks to measure the voltages. The second 

 selector switch is to select between an Amperite 4£^1 voltage-regulator tube and a fixed 1-ohm resistor 

 in series with the filament supply lead to the amplifier and oscillator. The regulator tube functions 

 for several weeks after a new filament battery has been installed, but after this period the battery 

 voltage drops below the control range of the regulator, and the 1-ohm resistance is then switched 

 into the circuit in order to extend the life of the battery. This switch is also used to turn off the 

 filament voltage. The push button is used only when testing or tuning the radio transmitter. Its 

 function is to short out the 1-megohm resistor of the silencing circuit. The rheostat control is for 

 adjusting the filament voltage of the keying tube. 



6524. Batteries 



Nine Burgess dry batteries supply the energy for operating the sono-radio buoy; their type 

 numbers are given in the circuit diagram, figure 134. The battery assembly weighs 53.5 pounds, exclu- 

 sive of the battery case. The total volume occupied by the batteries is approximately 1,147 cubic 

 inches. 



The total filament current consumption of the amplifier and radio transmitter is 0.38 ampere, 

 and the filament current of the keying tube is 0.06 ampere. The quiescent plate current consumption 

 of all circuits is about 2 milliamiieres, becoming about 40 milliamperes when the instrument is operated 

 by a bomb signal. 



One set of batteries and tubes can be expected to provide, on the average, for 30 to 40 days 

 continuous use of this type of sono-radio buoy. 



