AM (Amplitude Modulation) — AM radios control a model by varying the amplitude (height) of a radio signal. AM radios are the least costly, but the most affected by interference. See also FM (PPM) and PCM.

Analog — A radio that transmits control signals by changing voltage levels. Analog systems tend to cost less, which makes them ideal for beginners. See Digital.

ATL (Adjustable Throttxle Limiter) — This actually affects the braking action on a pistol, by limiting how far forward the trigger can move (travel.) May be adjusted mechanically, electronically or (rare) both ways.

ATV (Adjustable Travel Volume) — See EPA.

Band — The wavelength on which a radio transmits, as measured in megahertz (MHz) or gigahertz (GHz). There are currently five legal bands for R/C use: 72MHz (for air use), 75MHz (for surface use) and 27MHz, 50MHz and 2.4GHz, which can be used for either air or surface systems.

BEC (Battery Eliminator Circuitry) — BEC eliminates the need (and weight) of a receiver battery, by allowing the receiver to draw power from the power battery.

Buddy Box — A “dummy” (slave) transmitter used in flight training. Once connected via a trainer cord to a master radio, it: 1) allows the student to control the model remotely through the instructor’s radio, and 2) allows an instructor to take control whenever necessary.

Channel (as in a “2-channel radio”) — In general, it takes 1 channel to control one R/C function. A 2-channel radio is a 2-function radio.

Channel (as in “Channel 72”) — Here, “channel” means a specific frequency. Channels are identified by a number or by a letter and number.

Crystal (also Xtal) — Crystals control the radio signal’s frequency. Transmitter and receiver crystals must be on the same frequency. The exception: synthesized radio systems. (See below.)

Digital — A digital R/C system that transmits control input as a computer code and not by voltage levels as analog systems do. Generally, digital systems offer more set-up versatility and data storage (memory).

DSC (Direct Servo Control) — Allows you to link the transmitter and receiver with a cable, and check/adjust servo operation without broadcasting a signal. A high-end convenience.

D/R (Dual Rates) — This adjusts control sensitivity, or how far a servo will move with a given input. Low rates reduce it, slowing response — great for taming “skittish” models or helping newcomers avoid overcontrol. High rates speed and strengthen response.

EPA (Endpoint Adjustment. Also known as ATV) — Limits how far a servo arm can travel from the servo’s “center” or neutral position. EPA usually allows separate settings for either side of center. ATV may offer only one setting that affects both sides equally. Often found on throttle; also found on elevator and ailerons.

ESC (Electronic Speed Control) — Controls throttle electronically (through compact circuitry) rather than mechanically, with a heavier servo and linkage. Smoother and less complex, ESCs are available with reverse, brake or both.

Expo(nential) — Servo movement is usually linear, that is, in direct proportion to the input. A given input will always cause the same amount of movement. With exponential, a given input will cause different amounts of movement, depending on the control’s position. For example, a control surface can be set up to move at a lower rate near “center” stick, but at normal rates toward the “ends” of the stick.

Fail-safe — A safety feature. Automatically moves a servo (throttle or other) to a preset position when the signal to the receiver is lost.

Flight Pack — A package of on-board radio gear. Thrifty modelers buy flight packs that duplicate gear in an existing model, which allows them to use one radio with two (or more) models. Includes a receiver and servo(s), but may also include a NiCd and other items.

FM (Frequency Modulation) — FM radios control models by varying signal frequency. Though higher in price, they are much more interference-resistant.

Frequency Module (also RF Module) — Like a crystal, an RF module plugs into a transmitter and determines its frequency (channel).

GHz (GigaHertz) — A unit of measuring radio waves.

Glitch (also Hit) — A radio problem, most often caused by someone else transmitting on “your” channel (frequency).

Input — Short for control input. Input is using the features of your radio to control your model.

LCD (Liquid Crystal Display) — Frequently used on programmable radios to display menus, show settings, or provide constant data updates.

LED (Light Emitting Diode) — Often used as status lights.

Mode I — A flight radio on which the elevator and rudder are controlled by the left stick and the throttle and aileron are controlled by the right stick.

Mode II — A flight radio on which the throttle & rudder are controlled by the left stick and the aileron and elevator are controlled by the right stick. Most stick radios in the U.S. are Mode 2 radios.

MHz (Megahertz) — A unit of measurement for radio waves.

Mixing (also Coupling) — A radio function which allows the user to combine the functions of different channels and control them through a single control.

Modulation — The actual coded signal that’s sent via radio waves.

NiCd (Nickel Cadmium) Battery — An easy, affordable alternative to alkaline batteries. Alkaline cells are cheap, but must be purchased when power runs low. NiCds can be recharged and used hundreds of times. “Full” NiCds means that transmitter and receiver NiCds are included.

On-board Gear — The electronics in the model. Includes the receiver and servos, but can include the battery, ESC, fail-safe, etc.

PCM (Pulse Code Modulation) — PCM radios digitally encode signals, producing very strong, clear transmissions. Thought more expensive than AM or FM, PCM is far more interference-resistant.

Pistol (-Grip) Radio (also Wheel Radio) — A transmitter that has a pistol grip, a trigger for throttle and brake control and a wheel for steering.

PPM (Pulse Position Modulation) — see FM.

Proportional — A non-proportional control function offers only two choices: on or off, all or none. A proportional function provides a wide range of responses, based on the amount of input provided.

Receiver (also Rx) — An electronic device in the model that converts transmitter signals into electrical impulses for servos.

RF Module — See Frequency Module.

Runaway — A model that’s out of control. Whether it’s due to a glitch or a mechanical problem, it’s a danger to everyone.

Rx — Abbreviation for receiver.

Servo — The transmitter is the model’s brain. Servos are its muscles. The motor shaft in a servo rotates, which moves a servo arm. The arm is connected by linkages to a function. Control input makes the servo arm move and perform the function. As a rule, each function requires its own servo. Generally, systems include one or more servos. These may be analog or digital, and range in size from tiny Nanos™ to ¼ scale or “monster” types. Speeds, torque and features vary widely, depending on design and application.

Servo Center (also neutral) — The position a servo arm returns to when its control (stick, trigger, switch, etc.) is at its neutral position. (This depends on how a servo arm is installed.) Centering is how quickly and accurately a servo returns to center.

Servo Reversing — Reverses the way a servo rotates with the flip of a switch. A major convenience in servo mounting (installation).

Servo Tray — The place inside a model where servos are mounted (installed). Many also feature cutouts to speed mounting work.

Subtrims — Allow you to adjust a servo’s center point. This allows you to re-center the main trims without losing previous adjustments.

Sx — Abbreviation for servo.

Synthesis/Synthesized — A highly sophisticated alternative to crystals. Synthesized transmitters and receivers can be tuned to any channel (frequency) in a given radio band. Radios may include a synthesized transmitter, synthesized receiver or both.

Throttle Curve — A function which allows the user to slow or speed up throttle response in a specific part of the servo’s throw.

Throttle Trim — A function which allows the user to change the idle position/speed of a motor or engine.

Throw — A servo’s total range of travel.

Trainer System — With trainer system, an instructor can link his radio with a student’s radio (or buddy box) through a trainer cord. This allows the student to learn new skills, but also allows the instructor assume control to prevent crashes.

Transmitter (also Tx) — The hand-held part of a radio system. Stick transmitters are primarily for flight, robots and some scale models, while pistol (wheel) radios are common picks for cars, trucks and boats.

Trigger — The throttle and brake control on a pistol radio.

Trims — Adjust servo centering so you don’t have to hold a control input to make the model perform.

Triple Rates — A feature that allows you to create three (response) rates for a specific function or to adjust the “feel” of the model to your style.

Tx — Abbreviation for transmitter.

Wheel Radio — See Pistol radio.

Xtal — See crystal.

Y-harness — Wires and connectors that have been assembled into a “Y” shape for a specific use.