The Basic Telecommunication Signal System

Transmission medium connects the source and sink in telecommunication network. The transmission medium may comprise a network or a series of networks between source and sink.

The Transmission of Electrical Signal

The process of transmission of electrical signal through the network causes variation in size and shape of the complex waves or pulses carrying the information. The amplitude changes are termed as gains or losses in signal level. In addition, there are distributing effects like noise and distortion. When many channels of communication are established through a common transmission medium, there may be manual interference. The interference caused due to manual induction is called crosstalk.

SIGNAL DEFINITION 

Signal may be defined in following forms. 

• SIGNAL CONVEYING OF INFORMATION THROUGH A MEDIUM 

• The physical contents of a message. 

• A media directive or command conveying information or direction from one end of the transmission medium to another. Alternatively, the term “signal” may be defined on the basis of its nature or its use. The signal frequency and the signaling mode are the examples.

Signal types

Analog Signal

 Signals that follow the instantaneous variation of the signal information are defined as analog.

These signals continuously change over time. These signals can take any value within a certain range. These signals are constantly varying physical quantities. It’s expressing information of data through voltage, current, or frequency.

Digital Signal

A digital signal is in the form of a set of pulses or variations, which represent symbols in the clodified form. 

Digital signals are discrete in nature. It is represented by a series of pulses or discrete voltage levels. Digital signals transmit information by encoding them into binary code digits that are like (0 and 1 form). The quality of such signal is very good. These types of digital signals are mainly used to ensure data transmission over long distances.

Direct Current Signal 

Direct current signals are produced by the flow of electric current in one direction, magnitude of which is changed in accordance with the information. Accordingly, this system requires physical connecting lines and is limited by distance. 

Alternative Current Signal

Alternating current signals are suitable for transmission on long distances and high speeds.

Alternative Current signals periodically change the direction. Its commonly used for long distance area transmission and high-speed communication. These types of AC signals are commonly used in electrical power distribution and telecommunication services because their ability that travel to long distances areas without any loss or degradation.

Wave-form & Frequency 

Waveform and Frequency Sinusoidal is the simplest waveform and is illustrated in the figure. The time in second for a complete cycle is called period and the number of cycles in a second is called the frequency. The frequency is measured in hertz which represent one cycle per second.

Signal Wave Amplitude

The height of the wave is termed as its amplitude. Considering the trigonometry sine wave is similar to cosine wave, but it achieves maximum amplitude all 90° apart. The phase of a sinusoidal wave designate the angular difference between starting point and that of a sine wave itself. Amplitude, frequency, and phase represent the characteristics of a waveform that may varied so that symbols may be transmitted along the media. A message may comprise a number of such symbols.

Sound Waves 

Sound wave, commonly sound consider of longitudinal waves in the air, the term longitudinal means that the means of transmission is by oscillatory movement in the air particles, the direction of oscillation being the same as the direction of wave. The pitch of the voice is the fundamental frequency of the vocal cord vibration. The pitch range for male voice when speak is generally between 80 and 240 Hz and for female 140 to 500 Hz. The multiples of the fundamental frequency are called harmonics and or overtones. The second harmonic is double in frequency of the fundamental.

Signal Amplitude and phase Calculating Method

The method for calculating the amplitude and phase of the harmonics of a periodic wave-form from the itself is called “Fourier Analysis”. Any periodic wave-form regardless of the physical mechanism by which it is generated can be represented by a sum of harmonics in the way. In practice not all frequencies produced are transmitted to the receiver. It is more economic to use devices in circuits that have a limited bandwidth. As the receiving end of the speech or music the ear can only hear sounds that lie within certain limits.

The minimum sound level that can be detected by the ear is known as the threshold of audibility, with the sound level that produces a feeling of discomfort being known as the threshold of feeling. Figures illustrate the thresholds of feeling and audibility by putting sound pressure against frequency. It can be seen that the most sensitive region is 1,000 Hz to 2,000 Hz although response is capable with the 30Hz to 1,600500 Hz range.

Public Telephone ☎️

By international agreement the audio frequency for commercial quality speech circuit routed over is restricted from 300 Hz to 3400 Hz. The suppression of all frequencies above 3400Hz reduce the quality of sound but does not affect the intelligibility.