Analog & Digital Transmission

Analog and Digital Communication

Digital and Analog Signals

¢ Data is transmitted from one point to another point by means of electrical signals that may be in digital and analog form.

¢  In analog signal the transmission power varies over a continuous range with respect to sound, light and radio waves.

Analog Signal                                                                                                                      Analog Signal

¢ A digital signal may assume only discrete set of values within a given range. Examples are computer and computer related equipment.

¢ Analog signal is measured in Volts and its frequency in Hertz (Hz). A digital signal is a sequence of voltage represented in binary form.

Digital Signal

                                                                                         Digital Signal

¢ When digital data are to be sent over an analog form the digital signal must be converted to analog form.

¢  Modulation (conversion of digital to analog)

¢  Demodulation. (conversion of analog to digital)

¢ Modem.(device for conversion)

¢ In asynchronous transmission data is transmitted character by character as you go on typing on a keyboard. Hence there is irregular gaps between characters. However, it is cheaper to implement, as you do not have to save the data before sending.

¢  On the other hand, in the synchronous mode, the saved data is transmitted block by block. Each block can contain many characters.

Synchronous transmission is well suited for remote communication between a computer and related devices like card reader and printers

Data Transmission Modes

Data communication is the transmission of digital messages to external devices. If you look around your house, you will see many examples of data communication at work. Your cable system, your home phone and even your computer all work based on varying types of data transfer. The process of transmitting a message occurs millions of time a day without any of us being aware of it. Today’s recent data transfer methods include many complex concepts, but we can still break down the process to a few basic types.




  • A simplex communication system sends a message in only one direction. The message source works as the transmitter. It sends the message over the data channel to the receiver. The receiver is the destination of the message. Examples of simplex data communication include radio stations and TV broadcasts. With the simplex channel, there is no ability by the receiver to respond to the message. For example, a radio station plays a song on your car radio. The data transferred is the song. You do not have the opportunity to send a message back via your car radio to the station.

Half Duplex

  • A half-duplex data communication system provides messages in both directions but only allows transfer in one direction at a time. Once a party begins sending a transmission, the receiver must wait until the signal stops before responding. If the two data transfers attempt to send at the same time, they both fail. For instance, if you talk on a CB radio, you press a button and speak. If the receiver attempts to press the button and speak at the same time, neither one of you hear either message. The system is not capable of sending both ways simultaneously.

Full Duplex

  • A full duplex is a communication that works both ways at the same time. Essentially, full duplex data communication is a set of two simplex channels, one works as a forward channel and the other as a reserve channel. The two channels link together at some point. An example of a full duplex communication system is a landline telephone. When talking on a telephone, both parties have the ability to speak at the same time. The data, carried both ways through the telephone line, runs simultaneously.


  • Serial communication takes a data communication, breaks it up into small pieces, and sends the message one bit at a time through a channel. The receiver collects the small bits and reassembles them to compose the original message. Serial communication is the most common type of communication between electronic devices. One example of serial communication in action is the data sent from a modem to the service provider.








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