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There are many terms and jargon that are unique to just about every specialized field and radio control is not exception. We have put together this section to help familiarize you with some of those terms. We have broken the list into sections which you can access from the links at the right. This section will be under constant addition and revision.

Radio Terms
The following are some terms related to Radio Control Systems:

Adjustable Function Rate (AFR)
Similar to ATV, AFR allows end point adjustment independent of dual rate or exponential settings.
Adjustable Travel Volume (ATV)
An adjustment that lets you preset the maximum travel of a servo to either side of neutral.
Aileron Extension
The aileron extension (servo extension) is a cable with connectors on either end which goes between the receiver and a servo. This allows the servo to be placed at a greater distance from the receiver than the cable that comes on the servo will allow. It also permits easier removal of a wing when the servo that controls the aileron is mounted in the wing and the receiver is in the fuselage (which is usually the case). One aileron extension is usually included with a radio system of four or more channels. Aileron Extensions of various lengths are available from different manufacturers. Please note: long aileron extensions can sometimes cause radio interference problems unless “noise traps” are used.
Amplitude Modulation (AM)
Was initially the primary means of radio modulation used in R/C until recently. The control information is transmitted by varying the amplitude of the signal. AM is now used in only less sophisticated systems.
Buddy Box
The ability to connect two transmitters together for training purposes.
Channel
There are two definitions for the word channel in radio control. 1. It can refer to the channel number or frequency of operation of a control system. 2. It may also refer to one of the operating functions of a radio system. For example, a 4-channel radio system would have four control functions: aileron, rudder, throttle and elevator.
Crystal
An electronic component of the radio that determines the frequency of operation. There is one in the receiver and one in the transmitter.
Digital Trims
Digital trims utilize a spring loaded slide switch rather than a potentiometer to adjust trims using digital messages.
Direct Servo Controller (DSC)
Allows full function of an aircraft’s servos via an umbilical cord. This permits adjustment of radio functions without switching on the RF portion of a transmitter.
Dual Aileron Extension
The Y-Harness is a cable which plugs into a single channel in a receiver and two servos. This allows both servos to be operated from the same channel.
Dual Conversion
Dual conversion refers to the method in which the receiver processes the incoming signal. Generally a dual conversion receiver is less prone to outside interference and is the preferred type of receiver.
Dual Rates (D/R)
Dual Rate allows the modeler to choose between two different control sensitivities. With the dual rate switch in the “OFF” position, 100% servo throw is available for maximum control response. In some more sophisticated systems this “OFF” position may be adjusted to provide anywhere from 30% to 120% of normal full throw. In the “ON” position, servo throw is reduced and the control response is effectively desensitized. The amount of throw in the Dual Rate “ON” position is usually adjustable from 30% to 100% of total servo movement. The modeler can tailor the sensitivity of his model to his own preferences.
End Point Adjustment
The ability to adjust one end of a servo travel only. Similar to Adjustable Travel Volume, but for adjustment on one side of neutral only.
Exponential Rate
Exponential Rate is where the servo movement is not directly proportional to the amount of control stick movement. Over the first half of the stick travel, the servo moves less than the stick. This makes control response milder and smooths out level flight and normal flight maneuvers. Over the extreme half of the stick travel, the servo gradually catches up with the stick throw, achieving 100% servo travel at full stick throw for aerobatics or trouble situations.
Fail Safe (FS)
An electronically programmed mechanism in most PCM radios to automatically return a servo or servos to neutral or a preset position in case of radio malfunction or interference.
Flight Modes
The ability for a radio system to switch between different types of flying, particularly in helicopters. Different parameters may be committed to the transmitter’s memory and selected using a “flight mode” switch.
Frequency Flag
The frequency flag is a marker that is mounted on your transmitter to indicate what frequency your system is operating on to alert other modelers so as not to cause interference. See the section on frequencies below for more information on radio frequencies.
Frequency Modulation (FM)
Now the most common method of radio modulation in RC, FM is less prone to interference than AM. Information is transmitted by varying the frequency of the signal
Idle Up
The function of a helicopter radio to first bring the throttle and rotor speed up before adding collective pitch.
Mixing
Mixing is the ability to have one channel of control input at the transmitter affect more than one receiver channel and servo movement.
Mode I
The control stick configuration with the rudder and elevator being controlled by the left stick while the right stick controls the throttle and ailerons. This is popular in Europe.
Mode II
The control stick configuration with the ailerons and elevator being controlled by the right stick while the left stick controls the rudder and throttle. This is the normal set-up for aircraft in North America.
Mode IV
The control stick configuration with the rudder and elevator being controlled by the right stick while the left stick controls the ailerons and throttle. This is similar to Mode 1 except that the sticks are reversed. Some find this mode more desirable for flying aerobatics than the default Mode II.
Model Memory
Allows the storage of information for more than one model. Very convenient for only having to set reversing, trim, mixing, etc for a model once and still be able to use the transmitter for more than one model.
Modulation
The way the electronic control information is sent from your transmitter to the receiver through radio waves.
Noise Traps
A noise trap is a small electronic device which is wired into a long servo extension to reduce radio interference and to boost the control signal going to the servo. These are recommended for use where long servo leads are necessary.
Pitch Curve
The pitch curve is the relation between the position of your transmitter control stick for collective pitch and the actual pitch of the rotor blades. It is desirable to have adjustable pitch curve points on a helicopter radio—the more the better. That way one can customize the collective response according to the type of flying.
Pulse-Code Modulation (PCM)
A special digital encoding of a frequency modulated signal. FM is still utilized, however, the control information is in the form of a digital word rather than just a pulse width, as is used with standard AM or FM. Using PCM adds additional protection against interference from various sources.
Servo Control Arms
Servo Control Arms are the plastic output horns which are mounted to the output shaft on your servos. These come in various sizes and styles for different control applications. Most servos will come with an assortment of arms so you can customize to your own specific control needs.
Servo Extension
Same as aileron extension.
Servo Reversing
This feature allows the modeler to reverse a servo’s rotation direction at the flip of a switch. Permits servos to be mounted in the most convenient way without concern for their rotation direction. The proper movement can then be selected when the installation is completed.
Servo Torque
The measure of power of a servo as measured in ounce-inches (the number of oz. the servo can push with a 1” control arm)
Servo Tray
A Servo tray is a plastic tray which facilitates mounting your servos easily in your model. The tray is molded to hold your servos securely and ensure positive control to your control surfaces. Different trays may hold anywhere from one to four servos and are shaped for different uses and servo positions in your model.
Snap Roll Button
This feature is found on more complex radios and is used to perform a snap roll maneuver by simply pressing one button. The function is usually programmable to give a combination of rudder, elevator and aileron control.
Sub Trim
A radio function which allows very precise electronic centering of servos. Switch Harness - The switch harness is mounted in your model and it connects between your receiver and the NiCd battery pack. It provides a power ON/OFF switch to the radio in your model and it also allows your charger to be connected to your model’s battery pack for charging.
Synthesized Frequency
A more sophisticated method of controlling the frequency of a radio control system than crystals. Synthesizing is more expensive than crystals, however, it gives you the opportunity of selecting from a whole band of frequencies on which to operate. This allows you to obtain a clear frequency at the field—no more waiting for a crystal controlled frequency to become clear.
Trainer System
The trainer system feature allows two transmitters of similar design to be connected together via a cord (trainer cord) so that one transmitter may be used by an instructor and the second one by a student when learning to fly. The instructor simply has to hold a switch on his transmitter to give the student’s transmitter full control. If the student gets into trouble, the instructor can release the switch and he has full control of the model.
Variable Trace Rate (VTR)
This radio function is similar to exponential except it uses two linear responses to determine the servo sensitivity on the first and second half of the control stick movement.
Y-Harness
Same as a Dual Aileron Extension.

Programmable Mixing Terms
The following are some terms related to Programmable Mixing in Radio Systems:

Programmable Mixing is the electronic coupling of one channel to another. One control input will yield output to two different servos.

Aileron/Rudder Mixing
Adds rudder control when aileron is input from the transmitter aileron stick.
V-Tail Mixing
Used when there is a V-Tail on the aircraft rather than the conventional elevator and rudder. Each control surface of the V is connected to a separate servo. Operating the elevator control stick will move both surfaces up for back stick or both surfaces down for forward stick. Moving the rudder control stick left will move the left surface of the V down and the right surface up. Moving the rudder control stick to the right will move the left surface of the V up and the right surface down.
Flaperon Mixing
Mixes the Flap and Aileron functions so that when each aileron is connected to a separate servo (one servo plugged into the aileron channel and the other plugged into the flap channel), the surfaces will act as both ailerons and flaps, depending on the position of the controls.
Elevon Mixing
Mixes the elevator and aileron functions, especially useful for deltawing models where the elevator and ailerons are the same control surfaces. Each surface is connected to a separate servo (one servo plugged into the aileron channel and the other plugged into the elevator channel), the surfaces will act as both ailerons and elevator, depending on the position of the controls.
Flap/Elevator Mixing
Couples the flaps and elevators such that when the flaps are lowered, the elevator will be automatically adjusted to prevent pitching of the model.
Elevator/Flap Mixing
Couples the elevators and flaps such that when control is input to the elevators, the flaps will move in the opposite direction. This permits the model to perform tighter maneuvers in the pitch attitude.
Crow Mixing
Primarily used in gliders for spoiler action by mixing the flaps and ailerons. It is necessary for the ailerons to be using separate servos, plugged into separate channels and the flap servo to be independent of both aileron channels. Upon applying Crow Mixing, the flaps go down while both ailerons go up.
CCPM Mixing
Cyclic/Collective Pitch Mixing is used exclusively in helicopters and eliminates much of the complicated linkages required on a conventional setup. CCPM is a system which mounts 3 servos below the swashplate, with short, straight linkages directly to the swashplate at 120 degree intervals. With CCPM, complex collective and cyclic mixing is accomplished electronically, rather then mechanically. As a result, many parts are eliminated, along with excessive control system play—not to mention the quicker building time and lower required maintenance. Differential Ailerons - This type of mixing is accomplished by having separate servos on each aileron, plugging one into the aileron channel and the other into another unused channel. The two channels can be programmed to both operate from the aileron control stick, however the travel volume for each aileron may be adjusted separately giving more deflection in one direction (usually up) than in the other.