Just as FM radio is not generally affected by weather, neither are FSK transmissions. Therefore, ASK is not really suitable for transmission over long distances. On the other hand, any kind of amplitude modulated signal is very susceptible to outside interference. In analyzing methods for carrying digital data, Amplitude-Shift Keying is fairly easy to accomplish. The amplitude is varied in some technologies. Fig illustrates a couple of examples.Р вЂќР вЂЎigure 5.3: Frequency Modulation may be used to encode data into an analog signal as well.Р вЂќР вЂЎigure 5.4: Phase Modulation can be used to encode data in an analog signal. In the digital data realm, the same technology can be applied using Frequency-Shift Keying(FSK).

In this case, FM is an acronym for Frequency Modulation. For digital data, it's called Amplitude-Shift Keying (ASK).Р вЂќР вЂЎigure 5.2: Amplitude Modulation can be used to encode data in analog signals.Р вЂќР вЂЎSK : FM radio is produced by taking a basic signal (radio wave) and modulating its frequency according to another signal (i.e. We may use the same technology for carrying computer data as well. ASK:AM radio is produced by taking a basic signal (radio wave) and modulating its amplitude according to another signal (i.e. Phasing is the result of creating a signal out of sync with a reference signal.Altering the frequency, amplitude or phase of a signal is called modulation The figure below illustrates this more clearly. Thus as the reference signal is peaking, the phased signal is (for lack of a better term) troughing. If a signal is 180Р вЂ™РЎвЂќ out of phase, it means that as the reference signal reaches zero voltage following a peak, the phased signal begins. The level of non-synchronization is measured in degrees. One signal acts as a reference signal, the other signal is the phased signal. The measurement decibel is often used to describe the power of a signal.Р вЂќР вЂЎinally, phase describes the difference in the start of the cycle of one signal to the start of the cycle of another. The amplitude of analog waves is measured in watts, amps or volts.

This characteristic is called 'attenuation'. As analog data travels over distance, the amplitude of the wave decreases. Therefore, if there are 500 cycles per second for an analog signal, we say the frequency is 500 Hertz (500 Hz).Р вЂќР вЂћmplitude would be viewed as the height (peak) and the depth (trough) of the graphic wave. The name applied to the number of cycles per second is Hertz (Hz). When the current rises above zero, dips below zero and then returns to zero, we say the current has completed one 'cycle'. There are three factors to consider: frequency, amplitude, and phase.Р вЂќР вЂЎrequency is the rate at which the current alternates above and below the zero current level. If we were to graphically represent alternating current, it would appear as a wave, with voltage bouncing above and below the zero level. Analog data is carried by an alternating current.

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