Analog Communication Explained in a Comprehensive Manner

Communication:
The exchange of meaningful information is defined as communication (Exchanging Information). In today’s world, the development of internet communication and electronic media has given the concept of communication a global meaning, turning it into "global exchanging of information." Communication has technical, economic, social, and cultural dimensions. To achieve full, uninterrupted, and 100% communication, barriers to communication must be overcome.

Communication Barriers:

  • Distance
  • Attenuations in the transmission medium
  • Insufficient financial resources for following technological developments
  • Language and cultural differences

Providing the necessary technical equipment for communication over long distances falls under the domain of telecommunications. 


Elements of a Communication System

Transmitter:
Electronic circuits that encode or shape the signal to be transmitted into a form suitable for the medium. For example:

  • Radio transmitters: 1000 W–10 kW
  • Wireless transmitters: 2W–600W
  • Base stations: 25W
  • Mobile phones: 3W (500 mW in standby mode)

Transmission Medium:
The medium that carries the signal encoded by the transmitter. Transmission media can be divided into two types:

  • Guided (cabled)
  • Unguided (wireless/natural mediums)

Guided Transmission Media:
Includes mediums such as copper cable, twisted pair cables, coaxial cable, fiber-optic cables, and microwave guides.

Unguided Transmission Media:
Natural mediums like air, water, and vacuum.

Disturbances and Noise in Transmission Media:

  • Signal Attenuation: As communication distance increases, the signal weakens, and insufficient energy reaches the receiver.
  • Signal Distortion: Caused by different frequencies in the signal being attenuated differently as they propagate.
  • Delay Distortion (Dispersion): Results from different frequencies or light rays in fiber-optic cables taking different paths, reaching the target at varying times.
  • Noise: Any energy that disrupts the signal and unpredictably enters the system (e.g., sunlight, fluorescent lamps, motor ignition systems).

Types of Noise:

  1. Interference: Undesired signals entering the system and disrupting the main signal.
  2. Thermal Noise: Arising from free electrons in components like resistors and transistors due to ambient temperature (also known as Johnson noise or white noise).
  3. Intermodulation Noise: Harmonic frequencies of signals combining, leading to noise.
  4. Crosstalk: Signals in adjacent cables interfering with each other.
  5. Shot Noise: Noise originating in transistors.
  6. Impulse Noise: Noise caused by operational factors like electrical motors, ignition systems, or electromechanical relays.

Bell and Decibel:

As signals travel along a transmission line, they weaken. Repeaters amplify these signals back to the line. The logarithmic measure of this attenuation or amplification is termed a "Bell," named after Alexander Graham Bell.



  • Definition: When the amplitude of a carrier signal is varied in proportion to the information signal, it results in amplitude modulation.
  • Double Sideband Amplitude Modulation (DSB-AM): A modulator circuit produces amplitude modulation.

Radio Receivers

Superheterodyne Receiver:
Receives electromagnetic signals, amplifies them, and sends them to a speaker. Key properties include:

  1. Sensitivity: Ability to capture and amplify weak signals.
  2. Selectivity: Ability to filter out and isolate the desired signal from others.

Electronic Tuner:
A circuit composed of RF amplifiers, mixers, and local oscillators. It selects, amplifies, and extracts intermediate frequencies. If varicap diodes are used, it is termed an electronic tuner.


Frequency Modulation (FM):


  • Need: To address the signal-to-noise ratio problems at high power levels in AM systems. FM circuits include limiter circuits, PLL synthesizer circuits, and emphasis circuits.
  • Definition: The frequency of the carrier signal changes according to the amplitude of the information signal.

Advantages of FM:

  1. Higher sound quality due to reduced noise.
  2. Greater immunity to noise compared to AM.
  3. Capture Effect: FM systems prioritize stronger signals on the same frequency.
  4. Utilizes PLL synthesizer circuits.

Disadvantages of FM:

  1. Requires significantly larger bandwidth.
  2. More expensive circuits.
Stereo Transmitters and Receivers
The term "stereo" originates from a Greek word meaning "three-dimensional." In modern usage, it creates a three-dimensional effect with a two-source sound system placed at a certain distance from the listener. Stereo receivers and transmitters are designed to separate or create two-source signals, respectively. Stereo coding is incorporated into FM transmitters between the sound circuit and modulator.

Stereo coding procedures are standardized for compatibility with existing systems. A single-channel receiver can output both sound channels through one speaker, while a dual-channel receiver delivers stereo sound through two speakers.


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