In order to understand the working of our systems, we must first understand the basic operation of a servo.The servo we use today has evolved from a design implemented with the first proportional radios back in the 60's.

Let us look at one channel on your radio. At the transmitter we have a stick who's sole purpose is to control the "Length" (or width) of a pulse sent to your servo. How we generate and send this pulse in the transmitter, and how we receive and decode this pulse in the receiver, I will address later. For now lets accept that this occurs and see what happens.

Todays servos all use the same basic concept that the length of the pulse received controls the output arms rotational position. Although some of the early radio's used different pulse lengths, all current radios that I know of use a standard for the length of the pulse.

When your transmitter stick is centered, the pulse generated is 1.5 ms (milliseconds) long. As you move the stick to one end of its travel the pulse

either lengthens or shortens .5 ms (depending on the setting of your servo reverse switch to be explained under encoding). Looking at this overall we see that the pulse length then varies from 1.0 ms to 2.0 ms, with 1.5 ms being the center.

Now the goal of all transmitters is to encode this pulse onto a radio signal which can be received by the receiver and decoded back into the original pulse. What we get on the signal wire, going to the servo from the receiver, is a pulse which is varied in length from 1.0 to 2.0 ms depending upon where the transmitter stick is.   

Now how does the servo know where to rotate it's output arm to based on this pulse? For this we must look at the basic operation of the servo. (Referring to Figure 1)

Internally within a servo is its own pulse generator which generates a pulse which varies in length based on where the output arm is. Like the transmitter stick, the output arm moves a "variable resistor" (called a  "pot" for short). This varies the internal pulse generators pulse length from 1.0 to