Electrical Engineering > Communication Systems > Analog Communication

Analog communication is a fundamental branch within the broader field of communication systems in electrical engineering. It deals with the transmission and reception of data or information using continuous signals that vary over time. Unlike digital communication, which relies on discrete signals, analog communication transmits information in a format that closely resembles the original message.

Core Concepts

1. Analog Signals:
   • Analog signals are continuous waveforms that represent physical variables. Common examples include sinusoidal waves, which can be described by their amplitude, frequency, and phase.
   • Mathematically, an analog signal \( s(t) \) can be expressed as: \[ s(t) = A \sin(2 \pi f t + \phi) \] where \( A \) is the amplitude, \( f \) is the frequency, and \( \phi \) is the phase.
2. Modulation Techniques:

   • Amplitude Modulation (AM):
     Amplitude Modulation involves varying the amplitude of the carrier wave based on the message signal. The standard AM signal can be represented as:
     \[
     s(t) = [A + m(t)] \cos(2 \pi f_c t)
     \]
     where \( m(t) \) is the message signal, \( A \) is the carrier amplitude, and \( f_c \) is the carrier frequency.

   • Frequency Modulation (FM):
     Frequency Modulation changes the frequency of the carrier wave in accordance with the message signal. The FM signal is given by:
     \[
     s(t) = A \cos \left( 2 \pi f_c t + 2 \pi k_f \int_{-\infty}^{t} m(\tau) \, d\tau \right)
     \]
     where \( k_f \) is the frequency sensitivity of the modulator.

   • Phase Modulation (PM):
     Phase Modulation modifies the phase of the carrier signal as a function of the message signal. The expression for PM is:
     \[
     s(t) = A \cos \left( 2 \pi f_c t + k_p m(t) \right)
     \]
     where \( k_p \) is the phase sensitivity of the modulator.

3. Demodulation:
   • Demodulation is the process of extracting the original message signal from the modulated carrier wave. Techniques for demodulation match each modulation method like AM, FM, and PM.
   • For instance, in AM, envelope detectors are commonly used, whereas FM requires discriminator circuits.
4. Signal Quality and Noise:
   • Analog communication systems are susceptible to various kinds of noise, such as thermal noise, impulse noise, and intermodulation noise. These noise factors can degrade the signal quality during transmission and reception.
   • The Signal-to-Noise Ratio (SNR) is a critical metric for assessing the performance of an analog communication system: \[ \text{SNR} = \frac{P_s}{P_n} \] where \( P_s \) is the signal power and \( P_n \) is the noise power.

Applications

Analog communication was historically significant in many traditional systems, such as:
- Broadcast Radio
- Television Transmission
- Telephone Systems

Despite the advent of digital communication, analog techniques are still relevant in specific applications where high fidelity and real-time transmission are prioritized, like:
- High-fidelity audio broadcast (FM radio)
- Analog instrumentation and control systems

Conclusion

Analog communication forms the bedrock upon which modern communication systems have been built. Understanding the principles of analog signals, modulation, and noise mitigation is crucial for mastering the field of communication systems in electrical engineering. This knowledge provides a foundation for more advanced topics such as digital communication and information theory.