--- title: "Polar, unipolar, bipolar, Manchester; encode 101000111011" subject: "Data Communication" chapter: 5 key: "semester_5/data_communication:line-coding-101000111011" source: https://www.bctengineer.com/q/semester_5/data_communication/line-coding-101000111011 site: BCT Engineering --- # Polar, unipolar, bipolar, Manchester; encode 101000111011 Data Communication · Chapter 5: Data Encoding and Modulation - Asked in: 2070 Chaitra, 6+4 marks - Video: [Line Coding Techniques | RZ, NRZ, Unipolar, Polar, Bipolar & Manchester | Digital Communication](https://www.youtube.com/watch?v=daf9F9NC7zQ) — Engineering Funda - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/data_communication/line-coding-101000111011 - Whole chapter: https://www.bctengineer.com/md/semester_5/data_communication/chapter-5 ## Question Explain polar, unipolar, bipolar and Manchester coding with example. Encode the bit stream 101000111011 using all coding mentioned above. ## Short answer Unipolar NRZ: 1=+V, 0=0V. Polar NRZ-L: 1=+V, 0=-V. Bipolar AMI: 0=0V, 1s alternate ±V: +0-000+-+-0-+. Manchester: 1=low-to-high mid-bit transition, 0=high-to-low. ## Answer #### Unipolar coding Only one polarity is used: a 1 is +V and a 0 is 0 V (NRZ), so the DC component is large and long runs of the same bit give no clock. Simple and cheap, used in short links (inside a computer). #### Polar coding Two voltages of opposite polarity are used: for polar NRZ-L, 1 = +V and 0 = -V. The DC component is lower (zero if 0s and 1s are equal in number). Variants: NRZ-I, RZ, Manchester. #### Bipolar coding (AMI) Three levels: 0 = 0 V and 1s alternate between +V and -V. There is no DC component and violations detect errors. Long strings of 0s lose synchronisation (fixed by B8ZS/HDB3). #### Manchester coding A transition occurs in the middle of every bit: low-to-high for 1 and high-to-low for 0. It is self-clocking and has no DC component, but needs twice the bandwidth. It is used in 10 Mbps Ethernet. #### Encoding of 1 0 1 0 0 0 1 1 1 0 1 1 **Conventions used** (state these in the exam, as books differ): level before the first bit is low (-V); NRZ-L/RZ: 1 = +V, 0 = -V (unipolar: 0 = 0 V); NRZ-I: a 1 toggles the level at the start of the bit, a 0 keeps it; RZ: the pulse returns to zero in the middle of the bit; Manchester: 1 = low-to-high and 0 = high-to-low transition at mid-bit; differential Manchester: always a mid-bit transition, an extra transition at the start of the bit for a 0 and none for a 1; AMI: 0 = 0 V, 1s alternate +V and -V starting with +V. #### Unipolar NRZ ```text 1 0 1 0 0 0 1 1 1 0 1 1 +V ----| |---| |-----------| |------- 0 |---| |-----------| |---| ``` #### Polar NRZ-L ```text 1 0 1 0 0 0 1 1 1 0 1 1 +V ----| |---| |-----------| |------- 0 | | | | | | -V |---| |-----------| |---| ``` #### Bipolar AMI ```text 1 0 1 0 0 0 1 1 1 0 1 1 +V ----| |---| |---| |--- 0 |---| |-----------| | | |---| | -V |---| |---| |---| ``` #### Manchester ```text 1 0 1 0 0 0 1 1 1 0 1 1 +V |---| |---| |-| |-| |-| |-| |---| |-| |- 0 | | | | | | | | | | | | | | | | | -V --| |---| |-| |-| |---| |-| |-| |---| |-| ``` AMI pulses: + 0 - 0 0 0 + - + 0 - +. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the main drawback of unipolar coding? A. Large DC component and no clock for long runs of the same bit B. It needs twice the bandwidth C. It uses three levels D. It cannot represent 0 Answer: A. Only one polarity is used, so DC is large and long runs give no transitions. (Key point: Unipolar drawback) 2. How does bipolar AMI send 1s? A. Always +V B. Alternating +V and -V, with 0 as 0 V C. As a mid-bit transition D. As -V Answer: B. 1s alternate in polarity, giving no DC and allowing violation-based error detection. (Key point: Bipolar AMI) 3. What is the price of Manchester coding's self-clocking? A. It has a DC component B. It needs twice the bandwidth C. It needs three levels D. It cannot detect transitions Answer: B. Mid-bit transitions in every bit double the signalling rate and bandwidth. (Key point: Manchester cost) 4. For 1 0 1 0 0 0 1 1 1 0 1 1, what are the AMI pulses? A. + 0 - 0 0 0 + - + 0 - + B. + 0 + 0 0 0 + + + 0 + + C. + 0 - 0 0 0 - + - 0 + - D. - 0 + 0 0 0 - + - 0 + - Answer: A. The seven 1s alternate + - + - + - +, giving + 0 - 0 0 0 + - + 0 - +. (Key point: AMI pulses) ## Related in Data Communication - [Encode 1001101110 with unipolar, polar, bipolar codes](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aline-coding-1001101110) — Data Communication, chapter 5, asked 3× - [Encode 10110001110 with unipolar, polar, bipolar codes](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aline-coding-10110001110-68c) — Data Communication, chapter 5, asked 3× - [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: properties; encode 01001100011](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aline-coding-01001100011) — Data Communication, chapter 5 - [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 10010110001 with NRZ-L, NRZ-I, diff. Manchester](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aline-coding-10010110001) — Data Communication, chapter 5 ## Related in other subjects - [Definitions of unipolar, polar, bipolar, RZ, Manchester codes](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Adefine-line-codes) — Communication Systems, chapter 6, asked 2× - [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 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 100111010 (Polar RZ, bipolar NRZ, AMI, Manchester)](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aline-codes-100111010) — Communication Systems, chapter 6