- 2077 Chaitra (CS I) · 2+2+4 marks
Analog vs digital source; atmospheric noise
Short answer
Analog sources produce continuous waveforms, while digital sources output discrete symbols. Atmospheric noise from lightning causes impulsive interference, degrades AM severely, and accumulates along repeaters; FM is much less affected. Analog advantages include lower bandwidth, simpler hardware, no quantization noise, graceful degradation, and no conversion delay.
List out the differences between analog source and digital source. What are the effects of atmospheric noise in analog communication system. Mention the advantages of analog communication over digital communication system?
Analog source vs digital source
| Basis | Analog source | Digital source |
|---|---|---|
| Output | Continuous in time and amplitude | Finite set of discrete symbols |
| Values | Infinite possible values | Countable (e.g. 0/1, alphabet) |
| Examples | Microphone, thermometer, camera | Computer, keyboard, ADC output |
| Description | Waveform, bandwidth | Symbol rate, entropy (bits/symbol) |
Effects of atmospheric noise on analog communication
Atmospheric (static) noise is produced mainly by lightning discharges and other natural electrical disturbances in the atmosphere. It travels to the receiver like radio waves.
- It appears as impulsive crackling or "static" in AM radio and as spots on analog TV pictures.
- It is strongest at low and medium frequencies and falls as frequency increases; it is negligible above about 30 MHz.
- Since it is additive, it directly changes the amplitude of the received signal; AM is badly affected because the information is in the amplitude. FM is far less affected because a limiter removes amplitude variations.
- It reduces the SNR and fidelity of the received message and limits the usable range of LF/MF/HF links.
- In an analog system the noise cannot be separated from the signal once added, and repeaters amplify it along with the signal, so it accumulates over the link.
- It is worst in the tropics and in summer/rainy seasons when thunderstorms are frequent.
Advantages of analog over digital communication
- Less bandwidth: e.g. a voice channel needs about 4 kHz in AM-SSB versus 64 kbit/s (about 32 kHz or more) in PCM.
- Simpler and cheaper hardware: no ADC/DAC, coding or complex synchronization.
- No quantization noise: the signal is represented exactly, apart from added noise.
- Graceful degradation: quality falls slowly as SNR drops, instead of the sudden failure (cliff effect) seen in digital links.
- Real-time with no processing delay (no coding or buffering latency).
- Natural signals are already analog, so no conversion is needed.
✓ Answer checked by Claude Opus 5.5 (high effort)
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