---
title: "Analog and digital communication systems"
subject: "Instrumentation II"
chapter: 5
key: "semester_5/instrumentation_ii:analog-digital-comm-systems"
source: https://www.bctengineer.com/q/semester_5/instrumentation_ii/analog-digital-comm-systems
site: BCT Engineering
---

# Analog and digital communication systems

Instrumentation II · Chapter 5: Data Acquisition And Transmission

- Asked in: 2076 Asoj, 4 marks
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/instrumentation_ii/analog-digital-comm-systems
- Whole chapter: https://www.bctengineer.com/md/semester_5/instrumentation_ii/chapter-5

## Question

Discuss analog communication system and digital communication system with an appropriate block diagram.

## Short answer

Analog system directly modulates a carrier (AM/FM) with a continuous signal; simple but noise adds. Digital system samples, digitizes, source and channel codes, then modulates (e.g., PSK); regeneration prevents noise, errors can be corrected, and encryption is possible, but wider bandwidth and synchronisation are needed.

## Answer

#### Analog communication system
Information is a continuous signal (voice, video) that modulates a carrier continuously (AM, FM, PM).
```text
 Source -> Transducer -> Modulator -> Transmitter -> Channel (+ noise)
 Destination <- Transducer <- Demodulator <- Receiver <-----+
```
- Noise adds to the signal and cannot be removed; quality degrades with distance.
- Simple equipment, less bandwidth.
- Examples: AM/FM radio, analog TV, old telephone.

#### Digital communication system
Information is converted to bits, coded and sent as discrete symbols.
```text
 Source -> Sampler/ADC -> Source encoder -> Channel encoder
       -> Modulator (ASK/FSK/PSK) -> Channel (+ noise)
 Destination <- DAC <- Source decoder <- Channel decoder <- Demodulator
```
- Blocks: source encoding (compression, PCM), channel coding (error detection/correction), modulation, channel, and the reverse at the receiver.
- Signals can be regenerated by repeaters so noise does not accumulate; errors can be corrected; easy encryption, multiplexing (TDM), and processing.
- Needs more bandwidth and synchronisation; complex equipment.
- Examples: mobile phones, Ethernet, digital TV, Bluetooth.

| Point | Analog | Digital |
|---|---|---|
| Signal | Continuous | Discrete bits |
| Noise immunity | Poor | Good, with error control |
| Bandwidth | Less | More |
| Security and processing | Low | High |

## Check yourself

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

1. How does an analog communication system send information?
   A. Bits are coded as discrete symbols
   B. The signal is sampled and quantised
   C. A continuous signal modulates a carrier (AM, FM, PM)
   D. The carrier is never modulated
   Answer: C. Analog systems modulate the carrier continuously. (Key point: Analog system)

2. Which blocks does a digital system include beyond modulation?
   A. Only an amplifier
   B. Only a filter
   C. A transducer only
   D. Source encoding and channel coding
   Answer: D. Source coding compresses, channel coding detects and corrects errors. (Key point: Digital blocks)

3. Why is noise less harmful in digital systems?
   A. Signals can be regenerated and errors corrected
   B. Noise cannot reach them
   C. They need less bandwidth
   D. They use analog repeaters
   Answer: A. Repeaters regenerate pulses so noise doesn't accumulate. (Key point: Noise)

4. What is a drawback of digital systems?
   A. Poor security
   B. More bandwidth, synchronisation and complexity needed
   C. Noise buildup over distance
   D. Cannot be multiplexed
   Answer: B. Digital needs more bandwidth and complex equipment. (Key point: Drawback)

## Related in Instrumentation II

- [Digital transmission system; analog vs digital](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aanalog-digital-transmission-compare) — Instrumentation II, chapter 5
- [Advantages of digital over analog transmission](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Adigital-vs-analog-transmission-adv) — Instrumentation II, chapter 5
- [MBI block diagram and basic features](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Ambi-block-features) — Instrumentation II, chapter 1, asked 4×
- [MBI block diagram, advantages and DMA](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Ambi-block-advantages-dma) — Instrumentation II, chapter 1
- [MBI block diagram and advantages in industry](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Ambi-block-advantages) — Instrumentation II, chapter 1
- [Data logger block diagram and operation](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Adl-block) — Instrumentation II, chapter 5, asked 6×

## Related in other subjects

- [Digital vs analog communication; DCS block diagram](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Adigital-vs-analog-dcs-block) — Communication Systems, chapter 1
- [Modulation; analog communication system block diagram](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Amodulation-analog-block-diagram) — Communication Systems, chapter 1, asked 3×
- [Block diagram of analog communication system](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aanalog-comm-block-diagram) — Communication Systems, chapter 1, asked 2×
- [Block diagram of digital communication system](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Ablock-diagram-digital-comm) — Data Communication, chapter 1, asked 8×