Electronic Communication Systems

Introduction to Electronic Communication

• Communication: The exchange of information, including thoughts, ideas, and feelings, through verbal, nonverbal, print, or electronic means.
• Electronic Communication System: A system converts electrical signals into transmittable signals over a communication medium
• Transmitter: A circuit converts information into a signal suitable for transmission using components like oscillators, amplifiers, tuned circuits, modulators, and mixers.
• Communication Channel: The medium, transmits electronic signals via electrical conductors (wires, coaxial cables), optical media (fiber optics), and free space (radio waves).
• Receiver: It accepts and converts transmitted signals back into a human-understandable form. It has components like amplifiers, oscillators, mixers, filters, and demodulators.
• Transceiver: A device combining a transmitter and receiver, used for two-way communication in devices like telephones, radios, and modems.
• Attenuation: The degradation of a signal as it travels through a transmission medium, proportional to the square of the distance.
• Simplex Communication: One-way communication, like radio and TV broadcasting.
• Full-Duplex Communication: Two-way communication allowing simultaneous transmission and reception, like telephone conversations.
• Half-Duplex Communication: Two-way communication, where only one party can transmit at a time, such as walkie-talkies.
• Analog Signal: A signal varying continuously over time, for example, voice and video signals.
• Digital Signal: A signal changing in discrete steps or increments, for example, Morse code or binary data.
• Modulation: The process of varying a carrier signal’s amplitude, frequency, or phase to encode information for transmission.
• Multiplexing: A technique allowing multiple signals to be transmitted over a single communication medium; includes Time Division Multiplexing (TDM), Frequency Division Multiplexing (FDM), and Code Division Multiplexing (CDM).
• Electromagnetic Spectrum: The range of all electromagnetic waves; this includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.
• Bandwidth (BW): The portion of the electromagnetic spectrum occupied by a signal, it reflects the difference between upper and lower frequency limits.
• Spectrum Management: Regulation and allocation of the electromagnetic spectrum to ensure efficient use and avoid interference, managed by agencies like the FCC.

Electronic Fundamentals for Communication

• Gain: The increase in signal strength or amplitude, typically achieved through amplification.
• Attenuation: The reduction of signal strength or amplitude over a transmission path.
• Decibel (dB): A logarithmic unit used to measure gain or attenuation in signal processing.
• Tuned Circuit: A circuit with inductors and capacitors; it resonates at a specific frequency for filtering and signal selection.
• Capacitive Reactance (Xc): The opposition a capacitor presents to alternating current (AC), varying with frequency.
• Inductive Reactance (XL): The opposition an inductor presents to AC, proportional to frequency.
• Skin Effect: The tendency of AC to concentrate on the surface of a conductor at high frequencies, increasing resistance.
• Filter: A circuit selectively passing or attenuating specific frequency ranges, including low-pass, high-pass, bandpass, and band-reject filters.
• Fourier Theory: A mathematical method breaking down complex signals into a sum of sinusoidal components (harmonics).
• Harmonics: Integer multiples of a fundamental frequency that shape complex waveforms.
• Time Domain Representation: A graph showing signal variation over time.
• Frequency Domain Representation: A graph showing a signal's frequency components and their amplitudes.

Amplitude Modulation (AM) Fundamentals

• Amplitude Modulation (AM): A modulation technique where the amplitude of a high-frequency carrier signal varies according to the information signal.
• Modulation Index (m): A measure of carrier signal amplitude variation due to modulation, calculated as m = Vm/Vc.
• Overmodulation: Occurs when the modulation index exceeds 1, causing distortion in the transmitted signal.
• Sidebands: Additional frequencies generated when a carrier is modulated.
  • Upper Sideband (USB): Frequency components at fc + fm.
  • Lower Sideband (LSB): Frequency components at fc - fm.
• Bandwidth of AM: It is the total frequency range occupied by an AM signal, given by BW=fUSB-fLSB.
• AM Power Calculation: It is the total power in an AM signal, which is the sum of carrier power and sideband power: PT=PC+PLSB+PUSB.
• Single-Sideband Modulation (SSB): A technique eliminating one sideband to reduce bandwidth and power consumption.

Amplitude Modulator and Demodulator Circuits

• Double-Sideband Suppressed Carrier (DSB-SC): A modulation scheme removing the carrier and retaining both sidebands for efficiency.
• Vestigial Sideband (VSB): A modulation technique partially removing one sideband, commonly used in TV broadcasting.
• Low-Level Modulation: A modulation method generating signals at low power levels before amplification.
• High-Level Modulation: A modulation method amplifying the carrier before modulation, producing a strong signal for transmission.
• Diode Modulator: A simple circuit using a diode to create AM signals by mixing carrier and modulating signals.
• Transistor Modulator: A circuit that improves AM quality by using transistors to modulate the carrier signal.
• Collector Modulator: A high-level modulator where the modulating signal is applied to the collector of a transistor.
• Amplitude Demodulation: The process of extracting the original information signal from an AM wave.
• Diode Detector: A simple circuit rectifying the AM signal and filtering out the carrier to recover the original message.
• Crystal Radio Receiver: A basic AM receiver using a diode detector, requiring no external power source.
• Synchronous Detector: A demodulation circuit synchronizing with the incoming signal for improved signal quality.
• Balanced Modulator: A circuit generating a DSB-SC signal by suppressing the carrier and leaving only sidebands.
• Lattice Modulator: A type of balanced modulator using a diode bridge to generate suppressed-carrier signals.
• SSB Filter Method: A common method for generating SSB signals by removing one sideband using filters.
• Heterodyning: Mixing two frequencies to generate sum and difference frequencies, for demodulation.

Frequency and Phase Modulation

• Frequency Modulation (FM): Varying the carrier frequency according to the modulating signal, while the amplitude remains constant.
• Frequency Deviation: The maximum shift in carrier frequency from its original value due to modulation; a higher deviation improves sound quality but requires more bandwidth.
• Frequency Shift Keying (FSK): A digital modulation scheme where binary data is represented by discrete frequency shifts in the carrier.
• Phase Modulation (PM): Varying the carrier phase in accordance with the modulating signal, while the amplitude remains constant.
• Phase-Shift Keying (PSK): Digital modulation, where the carrier signal's phase changes according to digital data.
• Modulation Index (FM and PM): A measure of the extent of modulation.
• Bessel Functions: Mathematical functions used to analyze FM and PM sidebands.
• Carson’s Rule: Estimates the bandwidth required for FM transmission.
• Capture Effect: A phenomenon in FM where the strongest signal dominates over weaker interfering signals.
• Noise Immunity in FM: FM signals are less affected by noise because of their constant amplitude and limiter circuits eliminating amplitude variations.