Analog Transmission

Digital to Analog Transmission

The data is sent one device to another via analog carrier, and firstly it is converted into the analog signals. It modifies the analog signals to represent the digital data. This diagram shows the relationship between the digital-to-analog modulation process and the resulting analog signal.

The analog transmission defines the three basic methods:

1. ASK (Amplitude Shift-Keying)
2. FSK (Frequency Shift-Keying)
3. PSK (Phase Shift-Keying)

The fourth analog transmission is a combination of Amplitude shift keying and Phase shift keying, and that is called as the quadrature amplitude modulation (QAM).

Amplitude Shift Keying (ASK)

ASK is a type of modulation that reflects the amplitude of a carrier to the digital data as a variation. Frequency and phase remain constant even when the amplitude changes.

Frequency Shift Keying (FSK)

FSK is a type of modulation that reflects the frequency of a carrier to the digital data as a variation. The duration of a signal element is constant for a modulated signal, but when a signal element changes, the next signal element changes. For all signal elements are remain constant of the amplitude and phase.

Phase Shift Keying (PSK)

PSK is a type of modulation that reflects the phase of a carrier to the digital data as a variation. Amplitude and frequency remain constant even when the phase changes. PSK is more popular than ASK or FSK at today.

Quadrature Amplitude Modulation (QAM)

The combination of the ASK and PSK is called as the Quadrature amplitude modulation. The QAM is many types of variations possible.

Analog to Analog Transmission

It is the representation of the analog data by the analog signal. Modulation is required if only one bandpass channel is available to us. The best example of analog to analog transmission is a radio system. Each signal produces the analog signal.

There are three ways to achieve the analog-to-analog conversion:  

1. Amplitude Modulation (AM)
2. Frequency Modulation (FM)
3. Phase Modulation (PM)

Amplitude Modulation (AM)

The AM is a type of modulation that changes the high-frequency carrier signal into amplitudes of the modulating signal. The frequency and phase have the same for the carrier signal, but amplitude changes the data. The envelope of the carrier is the modulation signal.

The total AM bandwidth can be defined by the bandwidth of the audio signal: B_AM = 2B.

Frequency Modulation (FM)

In this transmission, the frequency of the carrier signal is modulated to changing the voltage level of the modulating signal. The top amplitude and phase of the carrier are constant, but as the information signal's amplitude changes, as such, the frequency of the carrier changes.

The total FM bandwidth can be defined by the bandwidth of the audio signal: B_FM = 2(1 * ?) B.

Phase Modulation (PM)

In this transmission, the phase of the carrier signal is modulated to changing the voltage level of the modulating signal. The top amplitude and frequency of the carrier are constant, but as the information signal's amplitude changes, as such, the phase of the carrier changes.

The total FM band-width can be defined by the bandwidth of the audio signal: B_PM = 2(1 + ?) B.