--- title: "Digital transmission system; analog vs digital" subject: "Instrumentation II" chapter: 5 key: "semester_5/instrumentation_ii:analog-digital-transmission-compare" source: https://www.bctengineer.com/q/semester_5/instrumentation_ii/analog-digital-transmission-compare site: BCT Engineering --- # Digital transmission system; analog vs digital Instrumentation II · Chapter 5: Data Acquisition And Transmission - Asked in: 2078 Kartik, 2+2 marks - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/instrumentation_ii/analog-digital-transmission-compare - Whole chapter: https://www.bctengineer.com/md/semester_5/instrumentation_ii/chapter-5 ## Question Draw the block diagram of a digital transmission system that can be used to transmit analog as well as digital data. Compare and contrast analog and digital transmission techniques with at least five distinguishing characteristics. ## Short answer A digital system samples and PCM-encodes analog data, then line-codes or modulates both analog-derived bits and digital data. Digital transmission offers regeneration, error control, encryption, constant quality, and TDM, but uses more bandwidth; analog is simpler, less bandwidth, but noise accumulates and quality degrades. ## Answer #### Block diagram of a digital transmission system for analog and digital data ```text Analog source -> LPF -> Sampler -> Quantiser -> Encoder (PCM) -+ v Digital source ------------------------------------> Line coder/Modulator | Channel | Analog output <- LPF <- DAC <- Decoder <- Regenerator/Demodulator Digital output <------------------------------------+ ``` Analog data is sampled (above twice the highest frequency), quantised and encoded into bits (PCM); digital data goes directly to the line coder or modulator (ASK, FSK, PSK). At the receiver the signal is regenerated, decoded and, for analog data, converted back by a DAC and filter. #### Comparison | Point | Analog transmission | Digital transmission | |---|---|---| | Signal | Continuous in time and amplitude | Discrete levels (bits) | | Noise effect | Noise adds up and cannot be removed | Regenerated by repeaters, errors can be detected and corrected | | Bandwidth | Less | More (for PCM) | | Equipment | Amplifiers, simple | Converters, repeaters, more complex | | Security / processing | Difficult to encrypt and process | Easy encryption, compression, multiplexing (TDM) | | Quality over distance | Degrades | Constant (regenerated) | | Examples | AM/FM radio, old telephone | Digital telephony, Ethernet, mobile data | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How is analog data prepared for a digital transmission system? A. Directly sent to the modulator B. Only amplified C. Converted using a DAC at the sender D. Low-pass filtered, sampled, quantised and encoded (PCM) Answer: D. Sampling must be above twice the highest frequency. (Key point: Analog to digital) 2. How do analog and digital transmission differ in handling noise? A. Analog noise adds up and cannot be removed; digital signals can be regenerated by repeaters B. Both can be regenerated C. Digital noise accumulates, analog does not D. Neither is affected by noise Answer: A. Regeneration stops noise accumulation in digital links. (Key point: Noise) 3. How does bandwidth compare? A. Analog needs more B. Analog needs less; digital (PCM) needs more C. They are the same D. Digital needs none Answer: B. The cost of digital transmission is larger bandwidth. (Key point: Bandwidth) 4. In the receiver, how is analog data recovered? A. Only a low-pass filter B. A quantiser and encoder C. Regenerator/demodulator, decoder, DAC and low-pass filter D. A multiplexer Answer: C. The DAC and filter rebuild the analog signal. (Key point: Receiver) ## Related in Instrumentation II - [Compact data logger characteristics and block diagram](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Acompact-dl-block) — 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 - [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× - [Analog and digital communication systems](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aanalog-digital-comm-systems) — Instrumentation II, chapter 5 - [Data transfer techniques for slow I/O](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aio-speed-mismatch) — Instrumentation II, chapter 1, asked 3× - [Error detection in serial data transmission](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aserial-error-detection) — Instrumentation II, chapter 3, asked 2× ## 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 - [Digital data acquisition system block diagram](https://www.bctengineer.com/question.md?key=semester_4%2Finstrumentation_i%3Adigital-data-acquisition-system) — Instrumentation I, chapter 6 - [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 - [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×