- 2075 Baisakh (CS I) · 4+2+2 marks
Noise vs interference; minimizing effects; need for modulation
Short answer
Noise is random unwanted energy from natural sources; interference is structured unwanted signals from man-made systems. Minimize noise by limiting receiver bandwidth, using low-noise amplifiers, and error-correcting codes; minimize interference by shielding, frequency planning, and directional antennas. Modulation is needed for practical antenna size, multiplexing, and improved noise immunity.
Distinguish between noise and interference? How their effects can be minimized? Also explain why modulation is needed in communication system.
Noise vs interference
| Basis | Noise | Interference |
|---|---|---|
| Definition | Random unwanted electrical energy | Unwanted signals from other sources |
| Origin | Natural/physical (thermal, atmospheric, cosmic) | Man-made systems (other transmitters, crosstalk) |
| Nature | Random, unpredictable | Usually structured, definite frequency |
| Spectrum | Broadband (often white) | Narrowband at specific frequencies |
| Example | Radio hiss, TV "snow" | Adjacent station, crosstalk, hum |
Minimizing their effects
Noise:
- Limit the receiver bandwidth to just the signal bandwidth (noise power ).
- Use low-noise amplifiers at the front end and cool sensitive receivers.
- Increase transmitted power or antenna gain to raise SNR.
- Use noise-resistant modulation (FM, PCM) and error-correcting codes.
- Use regenerative repeaters in digital links.
Interference:
- Proper frequency planning and guard bands; good selectivity (sharp IF filters).
- Shielding, grounding and twisted pairs to reduce crosstalk and hum.
- Directional antennas and polarization diversity.
- Choosing a high IF and good RF selectivity to reject image frequency.
- Spread-spectrum techniques and linear amplifiers to avoid intermodulation.
Why modulation is needed
- Antenna size: antenna length about ; baseband audio would need antennas many kilometres long, while a carrier of a few MHz needs only tens of metres.
- Multiplexing: allows many signals to share a channel on different carriers.
- Noise reduction: wideband FM improves the output SNR.
- Narrowbanding and equipment design become easier.
- Long-distance transmission and use of the frequency band allotted to the service.
✓ Answer checked by Claude Opus 5.5 (high effort)
Related questions
- External vs internal noise; interference sources; need for modulation · Communication Systems, chapter 1
- Reasons for modulation; noise vs distortion vs interference · Communication Systems, chapter 1
- Communication system block diagram; need for modulation · Communication Systems, chapter 1
- Noise vs interference and their limitations · Communication Systems, chapter 1
- Noise vs interference vs distortion · Communication Systems, chapter 1
- Distortion vs noise vs interference · Communication Systems, chapter 1
- What is modulation and why needed · Data Communication, chapter 5 · asked 4×
- Need of modulation; antenna parameters · Basic Electronics Engineering, chapter 5
- Short note: Interference in mobile communication · Wireless Communication, chapter 2
- Short note: Noise and its effects · Building Technology, chapter 1