ANTENNAS

RECEIVER TRANSFER SWITCHBOARD The receiver switchboard allows the audio outputs from the receivers to be transferred to remote control station audio circuits. A representative receiver trans- fer switchboard is shown in figure 1-12. This switch- board contains 10 seven-position switches. Each switch corresponds to a remote control station and each switch position (1 through 5) represents a re- ceiver. Position X allows the circuits attached to the switch to be transferred to another switchboard. ANTENNAS An antenna is a conductor or system of conductors that radiates or intercepts energy in the form of electro- magnetic waves. An antenna can be simply apiece of wire; but in practice, other considerations make the de- sign of an antenna system complex. The height above ground, conductivity of the earth, antenna shape and dimensions, nearby objects, and operating frequency are just a few of the factors affecting the radiation field pattern. Information on antenna theory, basic antennas, and wave propagation will be available in Antennas & Wave Propagation, volume 7, of this training series. Currently, you can find information in Navy Electric- ity and Electronics Training Series (NEETS), Module 10, Introduction to Wave Propagation, Transmission Lines, and Antennas, NAVEDTRA 172-10-00-83. SYNCHROS AND SERVOS In many electromechanical systems, the angular position of a shaft must be transmitted from one loca- tion to another without an actual mechanical linkage. You have seen examples of this in mast-mounted rotat- ing directional antennas and the automatic tuning func- tion of receivers and transmitters from remote locations. A widely used method employs ac machines that operate as single-phase transformers. These ma- chines are called synchros. Synchro receivers contain sets of gears that do the actual moving of the device to which the synchro is at- tached. These receivers are light-duty devices, de- Figure 1-12.—Receiver Transfer Switchboard (SB-973/SRT). signed to move small loads or to produce small amounts of torque. When the shaft to be driven at the remote location is connected to an indicating device or some light load, the synchro receiver is capable of de- veloping the necessary torque. But, if the load is a heavy load and more torque is required, torque (power) amplification is required. A control system capable of delivering larger amounts of power or torque is known as a servo mechanism, or servo. You will encounter many systems that use sychros and servos. You can find detailed information about these devices in the Military Standards Handbook, MIL-HDBK-225 and NEETS, Module 15, Synchros, Servos, and Gyros, NAVEDTRA 172-15-00-85. 1-13