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调制幅度信号

调制是指改变无线电或光波的幅度、频率或相位等以传送数据的过程。载波的特别之处在于它可以随着另一个“调制”波形发生瞬间改变。
调制信号的方法有很多：
振幅调制频率调制相位调制脉冲调制
相位调制还可以细分成几种调制方式，它们是：
脉冲调制（PM）
使用脉冲调制时，在一定时间间隔内，光波被多次拍摄“快照”（采取样本）。脉冲调制方式也有不少：
脉冲幅度调制脉冲编码调制脉冲频率调制脉冲位置调制脉冲宽度调制
脉冲位置调制（PPM）
脉冲位置调制定义：

也称脉冲时间调制。PPM是采用某种方法使同等振幅的脉冲信号以调制信号振幅禁止的比率生成。再次，这些随机比率生成的脉冲信号不能用TDM技术进行传输。这些信号的振幅和宽度在这个系统中始终如一。每个脉冲信号的位置都和周期性出现的基准脉冲相关联，它们和调制波瞬间采样的脉冲值不同。

Modulation Amplitude Signal
Published: 23, March 2015

Modulation is the procedure where a Radio Frequency or Light Wave's amplitude, frequency, or phase is changed in order to transmit data. The uniqueness of the carrier wave is that it instantaneously varied by another 'modulating' waveform. [1]

There are many ways to modulate a signal:

Amplitude Modulation Frequency Modulation Phase Modulation Pulse Modulation

The phase modulation additionally classified into few types which are; [1]

Pulse Modulation (PM)

With Pulse Modulation, a 'snapshot' (sample) of the waveform is taken at regular intervals. There are a variety of Pulse Modulation schemes:

Pulse Amplitude Modulation Pulse Code Modulation Pulse Frequency Modulation Pulse Position Modulation Pulse Width Modulation [1]

Pulse Position Modulation (PPM)

PPM Pulse Position Modulation definition:-

Also known as Pulse Time Modulation, PPM is a method where the pulses of equal amplitude are generated at a rate proscribed by the modulating signal's amplitude. Again, the random arrival rate of pulses makes this unsuitable for transmission using TDM techniques. The amplitude and width of the pulse is kept invariable in the system. The location of each pulse, in relation to the location of a recurrent reference pulse, is varied by each instantaneous sampled value of the modulating wave. PPM has the benefit of requiring constant transmitter power since the pulses are of constant amplitude and duration. It is widely used and it needs synchronization between transmitter and receiver.[2]

SOME DETAILS ABOUT PPM:-

The electronic scheme in the transmitter scans the positions of the sticks, pots and switches and creates eight pulses. Pulse length is linked to stick position, for example; all the way to the left 1 ms, middle 1.5 ms and all the way to the right 2 ms. Seven or Eight pulses according to the channels of the radio control system are put together and completed by a very long starting pulse to complete the frame-length of 22.5 ms. The starting pulse can vary between 22.5 -8*2 = 6.5 ms and 22.5-8*1 = 16.5ms,(Depending upon the channels which may be 7 or 8,the calculation will be accordingly). The 1-2ms pulses consist of 0.7 -1.7 ms High-Phase and 0.3 ms Low-Phase. The High-Phase is related with the f+b transmitter frequency, the Low-Phase with the f-b frequency. The transmitter switches between f+b and f-b. [3]

In order for a model to be proscribed in flight, the modeler must be able to input control movements which are sent to the model and translated into control surface movements. This is the main purpose of the radio control system. The radio transmitter has an input device, an encoder, a radio frequency (RF) section, and an antenna. Each part serve a specific purpose and each is required for t