---
title: "Short note: Distortion and interference"
subject: "Communication Systems"
chapter: 1
key: "semester_6/communication_systems:short-note-distortion-interference"
source: https://www.bctengineer.com/q/semester_6/communication_systems/short-note-distortion-interference
site: BCT Engineering
---

# Short note: Distortion and interference

Communication Systems · Chapter 1: Introduction

- Asked in: 2071 Magh (CS I), 4 marks
- Video: [1.2 Noise, distortion and interference | Communication System IOE](https://www.youtube.com/watch?v=kTfHdgxg5QY) — Saurab Poudel
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/communication_systems/short-note-distortion-interference
- Whole chapter: https://www.bctengineer.com/md/semester_6/communication_systems/chapter-1

## Question

Write a short note on distortion and interference.

## Short answer

Distortion is signal shape change caused by the system itself (amplitude/phase nonlinearities) and vanishes without signal; corrected by equalizers. Interference is unwanted external signals (other transmitters, crosstalk) present without the wanted signal, reduced by filtering and shielding.

## Answer

**Distortion** is the unwanted change in the shape of a signal caused by the system or channel itself; the output is no longer $K\,x(t - t_d)$.
- *Amplitude distortion:* gain not constant across the signal band.
- *Phase (delay) distortion:* phase not linear with frequency, so components arrive at different times (causes ISI).
- *Non-linear distortion:* non-linear devices generate harmonics and intermodulation products.
- It exists only when the signal is present and is deterministic, so it can be reduced by **equalizers**, linear amplifiers and pre-distortion.

**Interference** is contamination of the wanted signal by unwanted signals from **other sources**, mostly man-made.
- Examples: co-channel and adjacent-channel interference, crosstalk between cables, image-frequency signals, power-line hum.
- It is present even without the wanted signal and usually has a definite frequency.
- Reduced by good filtering and selectivity, shielding, frequency planning, directional antennas and spread spectrum.

| Distortion | Interference |
|---|---|
| Caused by the system itself | Caused by external signals |
| Vanishes with no signal | Present without signal |
| Fixed by equalization | Fixed by filtering/shielding |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which feature is true of distortion?
   A. It is random
   B. It exists even with no signal
   C. It comes from other transmitters
   D. It is caused by the system itself and vanishes when the signal is absent
   Answer: D. Distortion is a deterministic change due to the system and needs the signal. (Key point: Distortion)

2. Which is an example of interference?
   A. Clipping in an amplifier
   B. Phase nonlinearity of a cable
   C. Co-channel and adjacent-channel signals, crosstalk
   D. Thermal agitation
   Answer: C. Interference comes from other sources such as other stations or crosstalk. (Key point: Interference)

3. Distortion is mainly reduced by:
   A. Equalizers and linear amplifiers
   B. Shielding and frequency planning
   C. Spread spectrum only
   D. Directional antennas
   Answer: A. Interference needs filtering/shielding; distortion needs equalization or linear design. (Key point: Remedies)

## Related in Communication Systems

- [Noise vs interference vs distortion](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Anoise-interference-distortion) — Communication Systems, chapter 1
- [Distortion vs noise vs interference](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Adistortion-noise-interference-diff) — Communication Systems, chapter 1
- [Noise, distortion, interference; internal and external noise](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Anoise-types-internal-external) — Communication Systems, chapter 1
- [Noise, interference, distortion; thermal and high frequency noise](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Anoise-effects-thermal-hf) — Communication Systems, chapter 1
- [Reasons for modulation; noise vs distortion vs interference](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Amodulation-reasons-noise-distortion-compare) — Communication Systems, chapter 1
- [Distortion, noise, interference; four types of noise](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Adistortion-noise-interference-four-noise) — Communication Systems, chapter 1