Radio Equipment - basic functions

Radio equipment is usually characterised by the number of functions, or channels that it has. One channel provides a means of control over one function on a model - rudder for example; 8 channels provides control over 8 functions. These channels can be proportional - that is, when the control stick on the transmitter is moved it causes the corresponding control on the model to move, and the amount of control surface movement is proportional to the stick movement; a small stick movement produces a small control movement and so on - or it can be switched, that is, a switch on the transmitter causes the control to move from one position to another by a fixed amount.

The most basic equipment has two channels, or functions, which are usually operated by 2 separate sticks: one moves up and down, and one moves from side to side. This may be all that is required for a simple glider; one stick moves up and down to control the elevator and one moves from side to side to control the rudder.

The next step up is a set with 4 or more channels. In this case the controls are arranged as 2 sticks, each of which can move both up and down and side to side. These 4 functions are then used to operate throttle, rudder, elevator and aileron, although the exact arrangement of which stick operates which control can vary, depending on the mode of the transmitter. The 5th and 6th channels are switched and are operated by the switches on top of the case.

Radio Transmitter
This illustration shows a typical non-computerised 6 channel 35MHz FM radio transmitter, with an indication of the purpose of the various controls.

On - off switch Switches the set on, usually either a slide or rotary switch with a raised guard to help prevent accidental operation. Aerial A telescopic aerial which must be fully extended before operating the set. Some manufacturers use a shorter flexible aerial which is less prone to damage. Battery meter When switched on this meter indicates either the amount of power left in the battery pack. The meter has a scale divided into green for OK, amber for reduced power, and red for low power. Primary controls The control sticks are used to operate the primary flight controls: aileron, elevator, rudder and throttle. The first 3 are sprung so that the stick returns to its central position when released. The throttle stick has a ratchet mechanism so that it stays in the position selected. Trim adjustments As the sticks are spring loaded they have to be held off-centre if some degree of control input is required for level flight. By altering these ratcheted sliders permanent deflections of the control surfaces can be made allowing the sticks to be left at the sprung central position. They are used only to make temporary changes: any permanent trim deflection requires mechanical adjustment on the model.	Switched Channels The 5th and 6th channels of this set do not have proportional controls but are switched between 2 positions. This type of control may be used to operate functions such as a retractable undercarriage. Rate switches These toggle the total movement of a control between full movement and a preset reduction. When on, movement of the control stick will give a smaller than usual movement of the corresponding control surface. Rate adjusters a small rotary adjuster which allows the percentage reduction of movement of the control to be set. For example, rates may be set to give only 60% of available movement when on, and 100% of movement when off in order to increase the sensitivity of control surfaces when the engine stops and the slipstream effect across the tail surfaces is lost. Servo Reversing switches a set of small slide switches, one per channel, which reverses the direction of rotation of a servo in response to a control input. This can save a lot of time when installing the radio equipment into a model, as the connections can be made in the most convenient way and then the correct servo rotation direction selected on the transmitter.

On the back of the case you will find an access hatch for the battery pack, and a socket to plug in the battery charger. You may also find that the radio frequency (RF) module of the transmitter is removeable - this would enable the same transmitter to be converted from one frequency band to another, useful if you enjoy boats or cars as well as aeroplanes.

There will also be a facility to allow you to change crystals. The operating channel of the transmitter is set by plugging in an appropriate crystal: sometimes it is possible to plug them into an external socket, otherwise you may have to remove either the RF module or the back panel of the transmitter to change the crystal.

If the transmitter has a buddy box facility, then you will also find a socket somewhere on the case for the connecting lead, and there will be a spring-loaded switch to transfer control between transmitters.