Page 603 radio acoustic ranging 6512 



plate current to the radio-fretiuency amplifier may be measured. A switch is located in the filament 

 and plate-supply leads for turning on or off all the electric equipment. A key is provided by which the 

 transmitter can be turned on for tuning and testing purposes. 



6512. Keying Circuit 



Following the audio amplifier is the keying circuit, its purpose being to turn on the radio-frequency 

 transmitter at receipt of a bomb signal. The keying tube is a cold cathode gas-filled type OZ, installed 

 so that its anodes are connected across the secondary of the output transformer of the audio amplifier, 

 similar to a push-pull arrangement. The cathode is connected to the screen grid of the crystal-con- 

 trolled radio-frequency oscillator. A d-c potential of 90 volts is applied to the anodes of the type 

 OZ tube through the center tap of the output transformer. When a bomb signal is received and 

 amplified the voltage created between the anode and cathode of the keying tube is sufficient to cause 

 this tube to ionize and thereby conduct current, which applies a positive potential to the screen of the 

 oscillator tube, which at once starts to function. Because of the push-pull arrangement, full-wave 

 rectification occurs, adding to the efficiency of the keying circuit. 



6513. Radio Transmitter 



The radio transmitter is a crystal-controlled oscillator furnishing driving pow-er to a class C ampli- 

 fier. The oscillator tube is a pentode type IT 5 whose frequency is controlled by means of a quartz 

 crystal. This quartz crystal is a low temperature coefficient type, capable of maintaining the fre- 

 quency of the transmitter within one part per million per degree centigrade from 20° C. to 50° C. The 

 crystal is clamped in its holder so that it can be operated in any position. The holder is the so-called 

 Navy-type, composed of a cylindrical glazed isolantite body and a metal base on which the crystal 

 rests. The upper electrode is circular in shape and separated from the crystal by a small air g^p. 

 This electrode is adjustable so that the length of the air gap can be changed. Various frequencies 

 that are assigned to the Coast and Geodetic Survey in the range from 2492 to 4160 kc are used. 



The plate circuit of the oscillator is tuned, and connected to the power amplifier by capacitance 

 inductance coupling. The power amplifier tube is a IQ5 power-amplifier pentode, operating at the 

 same frequency as the oscillator, which therefore requires neutralizing to prevent oscillations. 



The transmitter is capable of delivering a radio-frequency power output of about 26 watts for a 

 very short period. This power output is sufficient for reasonably reliable R.A.R. operation even where 

 interference and static are prevalent. The high power output requires the use of a high plate potential 

 on the transmitting tubes. A resistance capacitance circuit in the plate-supply lead of the radio- 

 frequency oscillator and amplifier prevents high currents of long duration from damaging the trans- 

 mitter tubes. Before the transmitter is operated by a bomb signal the electrolitic condenser, connected 

 between the transmitter plate-supply lead and one side of the filainents, is charged to 360 volts or more. 

 When the transmitter operates, this condenser discharges into the oscillator and amplifier tubes, the 

 20,000-ohm resistance through which the condenser was charged limiting the transmitter plate current 

 to a safe value. With this arrangement the first and useful part of the radio signal will be of high 

 amplitude. In addition, the resistance-capacitance combination limits the length of the radio signal. 

 The advantage of this signal shortening is described in 6432. The power amplifier and the antenna 

 transmission line are coupled by means of link coupling. The transmission line connecting the 

 transmitter to the antenna circuit is a waterproof two-conductor cable about 4 feet long which enters 

 the drum and the antenna-coupling housing through stuffing boxes. The housing for the impedance- 

 matching circuit of the antenna coupler and the antenna are described in 2842(A). 



6514. Batteries 



The electric energy to operate the sono-radio buoy is derived from dry batteries. Burgess bat- 

 teries are used, and the type numbers are given on the circuit diagram, figure 133. The batteries 

 occupy a volume of 2,292 cubic inches, and weigh 109 pounds. Connections between the batteries 

 and the rest of the equipment are made by plug-in cables. 



The total amount of filament current required by the instrument is 0.25 ampere. The quiescent 

 plate current consumption of all the circuits is about 2 milliamperes. The total current is 90 milli- 

 amperes (peak meter reading) for the radio transmitter, when the instrument is operated by a bomb 

 signal. 



