1. Introduction to electronic communication systems
Electronic Communication Systems. Communication is the transfer of meaningful information from one location to another. The following definitions are relating to terms applied to communication systems.

2. An analogue signal:-
An electrical signal that varies continuously in amplitude or frequency with the information being transmitted

3. A Digital signal:-
A way of sending voice, video, or data that reconstructs the signals using binary codes (1s and 0s) for transmission through wire, fiber optic cable, video conference,

4. Transmission medium:-
The material on which information signals may be carried; eg, optical fiber, coaxial cable, and twisted-wire pairs.

5. a radio wave that can be modulated in order to transmit a signal
carrier wave:
a radio wave that can be modulated in order to transmit a signal

6. the activity of converting data or information into code
Encoding:-
the activity of converting data or information into code

7. The process of converting coded data into its original format.
Decoding:-
The process of converting coded data into its original format.

8. Modulation:-
The process of modifying a carrier wave in such a way that the modification(s) to the wave represent information. Transmitting modems use modulation to load information onto a telephone signal (carrier).

9. Demodulation:-
Demodulation is the process of recovering the original modulating signal from a modulated carrier. The original modulating signal is usually the information signal.

10. Gain:-
amplification: the amount of increase in signal power or voltage or current expressed as the ratio of output to input

11. Attenuation:-
The decrease in the power of a signal, light beam, or light wave. Measured in decibels. Opposite of gain.

12. Base(signal)Bandwidth:-
In electronic communication, bandwidth is the width of the range (or band) of frequencies that an electronic signal uses on a given transmission medium. In this usage, bandwidth is expressed in terms of the difference between the highest-frequency signal component and the lowest-frequency signal component.

13. Channel(Broadcast) Bandwidth:-
The bandwidth of a channel is the difference between the lowest and highest frequencies that can be transmitted in that channel without significant loss.

14. Noise:-
In common use, the word noise means unwanted sound or noise pollution. In electronics noise can refer to the electronic signal corresponding to acoustic noise (in an audio system) or the electronic signal corresponding to the (visual) noise commonly seen as 'snow' on a degraded television. Generally in electronic circuitry noise refers to electromagnetic interference from an external source.

15. Distortion:-
Generally in electronic systems distortion refers to signal interference from internal circuitry.
eg Clipping distortion of an Op-Amp or the random motion of electrons within the circuit itself.

16. Multiplexing:-
Transmitting multiple signals over a single communications line or computer channel. The two common multiplexing techniques are frequency division multiplexing, which separates signals by modulating the data onto different carrier frequencies, and time division multiplexing.

17. Demultiplexing:-
This is the opposite function to multiplexing ie. The signal from the single transmission line is directed to one of many outputs.

18. Time Division multiplexing:-
This a method of conveying many signals on a single channel. Signals from several sources are allocated to short time slots and transmitted one after another in short succession. At the receiver the signals are sorted and routed to their proper recipients.

19. Error checking:-
This refers to the use of a parity bit as a means of checking the digital signal for any corruption or error.

20. Frequency division multiplexing:-
This approach sends a number of different messages or signals which are modulated on to a number of different frequencies and sent down the same channel at the same time. They are then separated at the receiving end.

21. Frequency Shift Keying(FSK):-
FSK is a technique for transmitting digital information as an analogue signal. It is used, for example, in transmitting digital data from a computer to an Internet Service Provider over a public telephone line. The system is based on two audio frequencies, one of which represents ‘0’ and the other ‘1’. In one version of FSK, a ‘0’ is represented by a burst of 4 cycles at 1.2KHz, and a ‘1’ is represented by a burst of 8 cycles at 2.4KHz. The digital signals are converted into FSK, and FSK converted back into digital signals by a modem (modulator/demodulator) which connects the computer with the telephone line.

23. The relationship between bandwidth, data rate and the capacity to carry information.
Modems. Ordinary copper telephone lines are designed to carry audio frequency signals in the range 300hz to 3500Hz. They are not meant to handle long strings of fast-rising and falling d.c pulses which would be affected by capacitive and inductive effects.
However, digital data can be sent over the telephone network so long as there is a device called a modem at each end.
Bit-rate.Digital data is sent in bits, ie 1s and 0s, and the rate at which transmission occurs is measured in bauds where
1 baud=1 bit per second
The greater the bandwidth of the telephone line, the greater the range of frequencies it can transmit satisfactorily, the greater the bit rate it can transmit. This is because each bit of data requires as a maximum, one cycle of audio tone. Therefore the higher the tone frequency the more bursts can be ‘fitted in’ but this depends on the bandwidth of the line.