RGKThe symbol used to express the resistance between the grid and the cathode of an electron tube .
RHEOSTATA variable resistor used for the purpose of adjusting the current in a circuit  .
RHOGreek letter "rho" ( ). Used in the field of electricity and electronics to represent the specific
resistance of a substance .
RHOMBIC ANTENNAA diamond-shaped antenna used widely for long-distance, high-frequency
transmission and reception .
RIGID COAXIAL LINEA coaxial line consisting of a central insulated wire (inner conductor) mounted
inside of a tubular outer conductor .
RIGIDITYThe tendency of the spin axis of a gyro wheel to remain in a fixed direction in space if no
force is applied to it .
RINGINGRF oscillations caused by shock excitation of a resonant circuit or cavity .
RING TIMEIn radar, the time during which the output of an echo box remains above a specified level
RIPPLE FREQUENCYThe frequency of the ripple current. In a full-wave rectifier it is twice the input-
line frequency .
RIPPLE VOLTAGEThe alternating component of unidirectional voltage. (This component is small
compared to the direct component.) 
RLC CIRCUITAn electrical circuit that has the properties of resistance, inductance, and capacitance .
RL DIFFERENTIATORAn RL circuit in which the output is taken from the inductor .
RL INTEGRATORAn RL circuit in which the output is taken from the resistor .
RMSAbbreviation of root mean square .
ROOT MEAN SQUARE (RMS)The equivalent heating value of an alternating current or voltage, as
compared to a direct current or voltage. It is 0.707 times the peak value of a sine wave .
ROTARY CAPA spark gap, similar to a mechanically driven rotary switch, used to discharge a pulse-
forming network .
ROTARY SWITCHA multicontact switch with contacts arranged in a circular or semicircular manner
ROTATING FIELDThe magnetic field in a multiphase ac motor that is the result of field windings being
energized by out-of-phase currents. In effect, the magnetic field is made to rotate electrically rather than
ROTATING JOINTA joint that permits one section of a transmission line or waveguide to rotate
continuously with respect to another while passing energy through the joint. Also called a rotary