--- title: "Line coding 1011000010000000001 (polar NRZ, AMI, Manchester)" subject: "Communication Systems" chapter: 6 key: "semester_6/communication_systems:line-codes-polar-ami-manchester-long" source: https://www.bctengineer.com/q/semester_6/communication_systems/line-codes-polar-ami-manchester-long site: BCT Engineering --- # Line coding 1011000010000000001 (polar NRZ, AMI, Manchester) Communication Systems · Chapter 6: Baseband Digital Data Transmission - Asked in: 2074 Chaitra (CS II), 6 marks - Video: [Line coding in digital communication- Polar, Unipolar, Bipolar, RZ ,NRZ in simple way | HINDI](https://www.youtube.com/watch?v=rHPa0VU27l0) — Electronics Subjectified - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/communication_systems/line-codes-polar-ami-manchester-long - Whole chapter: https://www.bctengineer.com/md/semester_6/communication_systems/chapter-6 ## Question Draw the timing diagram of Polar NRZ, AMI and Manchester for the following binary sequence 1011000010000000001. ## Short answer Polar NRZ: 1 is +V, 0 is -V. AMI: 1 alternates +V/-V, 0 is 0 V. Manchester: 1 is +V then -V, 0 is -V then +V. Long zero runs cause DC in NRZ and timing loss in AMI, while Manchester is self-clocking. ## Answer Conventions (bit period $T_b$, amplitude $V$): | Code | Bit 1 | Bit 0 | |---|---|---| | Polar NRZ | $+V$ for full bit | $-V$ for full bit | | AMI (bipolar) | $+V$ and $-V$ alternately | 0 | | Manchester | $+V$ then $-V$ (high-to-low at mid-bit) | $-V$ then $+V$ (low-to-high) | The first 1 in AMI is taken as $+V$ (full-width pulses). Bit sequence (19 bits): **1 0 1 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 1** Each character below is half a bit period. ```text bits 1 0 1 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 1 Polar NRZ: +V |‾‾ ‾‾‾‾ ‾‾ ‾‾ 0 | -V | __ ________ __________________ AMI (bipolar NRZ): +V |‾‾ ‾‾ ‾‾ 0 | -- -------- ------------------ -V | __ __ Manchester: +V |‾ ‾‾ ‾ ‾ ‾ ‾ ‾‾ ‾ ‾ ‾ ‾ ‾ ‾ ‾ ‾ ‾‾ 0 | -V | __ _ __ _ _ _ __ _ _ _ _ _ _ _ _ _ ``` AMI levels of the five 1s (bits 1, 3, 4, 9, 19): $+V, -V, +V, -V, +V$. Observations: - **Polar NRZ:** stays at $-V$ for the run of nine 0s (bits 10–18), so there are no transitions for timing recovery, and the waveform has a DC component. - **AMI:** zero DC because 1s alternate; a violation of alternation shows an error. But the long run of zeros gives 0 V for 9 bits, so timing is lost (solved by B8ZS or HDB3). - **Manchester:** has a mid-bit transition in every bit, including the zero run, so it is self-clocking with no DC; it needs twice the bandwidth of NRZ. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. In the sequence 1011000010000000001 the five 1s in AMI are: A. +V, -V, +V, -V, +V B. +V, +V, +V, +V, +V C. +V, -V, -V, +V, +V D. -V, +V, -V, +V, -V Answer: A. AMI alternates polarity on successive 1s, starting with +V. (Key point: AMI levels) 2. What is the weakness of AMI in a long run of zeros? A. DC builds up B. 0 V for many bits, so timing is lost (fixed by B8ZS or HDB3) C. Amplitude doubles D. It becomes unipolar Answer: B. Zeros give no pulses; B8ZS/HDB3 insert violations to keep transitions. (Key point: Zero run in AMI) 3. During nine consecutive 0s, Polar NRZ: A. Alternates between +V and -V B. Stays at -V with no transitions and has DC C. Is at 0 V D. Stays at +V Answer: B. A constant -V gives no timing information and a DC component. (Key point: Polar NRZ zero run) 4. Why is Manchester self-clocking? A. It has a mid-bit transition in every bit B. It uses half the bandwidth C. It has three levels D. It transitions only on 1s Answer: A. Every bit, including zeros, has a mid-bit transition, so the clock can be recovered, at twice the NRZ bandwidth. (Key point: Manchester self-clocking) ## Close variants set in other exams - [Line coding 1011000010000000000111](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aline-codes-long-sequence) — Communication Systems, chapter 6, asked 2× ## Related in Communication Systems - [Line coding 1011001010 (polar NRZ, polar RZ, Manchester, AMI)](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aline-codes-1011001010) — Communication Systems, chapter 6, asked 8× - [Line coding 1001001101 (polar NRZ, polar RZ, Manchester, AMI)](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aline-codes-1001001101) — Communication Systems, chapter 6, asked 8× - [Line coding 1001101101 (unipolar NRZ, polar RZ, AMI, Manchester)](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aline-codes-1001101101) — Communication Systems, chapter 6, asked 8× - [Line coding 1101010111 (polar NRZ, polar RZ, Manchester, AMI)](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aline-codes-1101010111-polar-ami) — Communication Systems, chapter 6, asked 8× - [Line coding 10110101 (polar NRZ, unipolar RZ, AMI, Manchester)](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aline-codes-10110101) — Communication Systems, chapter 6, asked 8× - [Line coding 1101010011 (polar NRZ, polar RZ, Manchester, AMI)](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aline-codes-1101010011) — Communication Systems, chapter 6, asked 8× ## Related in other subjects - [Encode 1101001 with polar NRZ, AMI, Manchester](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aline-coding-1101001) — Data Communication, chapter 5, asked 3× - [Line coding and NRZ, RZ, AMI](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aline-coding-nrz-rz-ami) — Telecommunications, chapter 3 - [Line coding: polar RZ and bipolar AMI](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aline-coding-polar-rz-ami) — Data Communication, chapter 5 - [Encode 10101111000011 with NRZ, RZ, AMI, Manchester](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aline-coding-10101111000011) — Data Communication, chapter 5