--- title: "Block diagram of analog communication system" subject: "Communication Systems" chapter: 1 key: "semester_6/communication_systems:analog-comm-block-diagram" source: https://www.bctengineer.com/q/semester_6/communication_systems/analog-comm-block-diagram site: BCT Engineering --- # Block diagram of analog communication system Communication Systems · Chapter 1: Introduction - Asked in: 2074 Bhadra (CS I), 8 marks; 2071 Magh (CS I), 6 marks (asked 2 times) - Video: [Introduction to Analog and Digital Communication | The Basic Block Diagram of Communication System](https://www.youtube.com/watch?v=qhjj6WG7Rgc) — ALL ABOUT ELECTRONICS - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/communication_systems/analog-comm-block-diagram - Whole chapter: https://www.bctengineer.com/md/semester_6/communication_systems/chapter-1 ## Question Draw and explain the block diagram of analog communication system. ## Short answer The analog communication system consists of information source, input transducer, transmitter (modulator/amplifier), channel (adds noise), receiver (demodulator/filters), output transducer, and destination. The message is converted to an electrical signal, modulated onto a carrier, transmitted, received, demodulated, and converted back to its original form. ## Answer An **analog communication system** sends a continuously varying message (voice, music, video) from a source to a destination through a channel, usually using analog modulation such as AM or FM. ```text +--------+ +----------+ +-----------+ | Info |->| Input |->|Transmitter| | source | |transducer| |(modulator)| +--------+ +----------+ +-----------+ | v +-----------+ Noise ---->| Channel | +-----------+ | v +--------+ +----------+ +-----------+ | Desti- |<-| Output |<-| Receiver | | nation | |transducer| |(demod.) | +--------+ +----------+ +-----------+ ``` #### 1. Information source Produces the message to be sent, e.g. human speech, music, a picture or a sensor reading. In analog systems the message takes continuous values. #### 2. Input transducer Converts the non-electrical message into an electrical signal called the **baseband** or **message signal** $m(t)$. Examples: microphone (sound to voltage), camera (light to voltage). #### 3. Transmitter Makes the message suitable for the channel. Main parts: - **Modulator:** varies a parameter (amplitude, frequency or phase) of a high-frequency carrier $A_c\cos 2\pi f_c t$ according to $m(t)$, giving AM, FM or PM. - **Filters and amplifiers:** limit the bandwidth and raise the power to the required level. - **Antenna** (in radio systems): radiates the signal. #### 4. Channel The physical medium between transmitter and receiver: free space, coaxial cable, twisted pair, optical fibre, waveguide. While passing through the channel the signal is: - **attenuated** (loses power), - **distorted** (by limited bandwidth, non-linearity, multipath), - corrupted by **noise** and **interference**, added mostly here and at the receiver front end. #### 5. Receiver Recovers the message from the weak, noisy received signal. It includes an RF amplifier, mixer and IF amplifier (in superheterodyne receivers), filters that reject noise and adjacent channels, and the **demodulator/detector**, which extracts $m(t)$ from the carrier. #### 6. Output transducer Converts the recovered electrical signal back into its original form, e.g. loudspeaker (voltage to sound), picture tube/LCD (voltage to image). #### 7. Destination The person or device that uses the message. **Example:** in AM radio broadcasting, the studio microphone is the input transducer, the AM transmitter and antenna form the transmitter, free space is the channel, and the home radio (superheterodyne receiver with envelope detector and loudspeaker) is the receiver and output transducer. The quality of an analog system is measured mainly by the **output signal-to-noise ratio** and the **fidelity** (how closely the output follows the original message). ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the job of the input transducer in an analog communication system? A. Modulate the message onto a carrier B. Convert the non-electrical message into an electrical baseband signal m(t) C. Remove noise from the channel D. Amplify the received signal Answer: B. A microphone or camera converts sound or light into the electrical message signal called baseband. (Key point: Input transducer) 2. What does the modulator in the transmitter do? A. Converts the electrical signal back to sound B. Adds noise to the message C. Varies amplitude, frequency or phase of a high-frequency carrier according to m(t) D. Samples the message at a fixed rate Answer: C. Modulation varies a carrier parameter in step with the message, giving AM, FM or PM. (Key point: Role of the modulator) 3. What happens to the signal in the channel? A. It is demodulated B. It is attenuated and distorted, and noise and interference are added C. It is amplified without distortion D. It is converted to digital form Answer: B. The channel attenuates and distorts the signal and noise and interference are added mainly there and at the receiver front end. (Key point: Where degradation occurs) 4. Which pair is the main measure of quality of an analog communication system? A. Bit error rate and data rate B. Output SNR and fidelity C. Antenna height and carrier frequency D. Number of repeaters and cost Answer: B. Analog systems are judged by output signal-to-noise ratio and fidelity; BER is the digital measure. (Key point: Quality measures) ## Related in Communication Systems - [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× - [Analog communication block diagram; modulation and its reasons](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aanalog-comm-modulation-reasons) — Communication Systems, chapter 1, asked 3× - [Analog communication block diagram; FDM of three signals](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aanalog-block-fdm-three-signals) — Communication Systems, chapter 5 - [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 - [Communication system block diagram; need for modulation](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Acomm-block-diagram-needs-modulation) — Communication Systems, chapter 1 - [Analog and digital system block diagrams; linear and non-linear distortion](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aanalog-digital-block-linear-nonlinear-distortion) — Communication Systems, chapter 1 ## Related in other subjects - [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× - [Communication system and block diagram](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Acomm-system-block-diagram) — Basic Electronics Engineering, chapter 5, asked 7× - [Communication system and AM block diagram](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Adefine-comm-am) — Basic Electronics Engineering, chapter 5 - [Digital control system block diagram and advantages](https://www.bctengineer.com/question.md?key=semester_6%2Fdigital_control_system%3Adcs-block-diagram-advantages) — Digital Control System, chapter 1, asked 3×