--- title: "Guided and unguided transmission media" subject: "Telecommunications" chapter: 2 key: "semester_8/telecommunications:transmission-media-explain" source: https://www.bctengineer.com/q/semester_8/telecommunications/transmission-media-explain site: BCT Engineering --- # Guided and unguided transmission media Telecommunications Β· Chapter 2: Transmission Media - Asked in: 2080 Bhadra, 8 marks; 2074 Asoj, 8 marks (asked 2 times) - Video: [CN 5 : Transmission Media | Guided & Unguided Media with Examples](https://www.youtube.com/watch?v=HryzQDpKvwA) β€” CS & IT Tutorials by Vrushali πŸ‘©β€πŸŽ“ - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/telecommunications/transmission-media-explain - Whole chapter: https://www.bctengineer.com/md/semester_8/telecommunications/chapter-2 ## Question What are the transmission media used in telecommunication? Explain with suitable diagram guided and unguided transmission media used in telecommunication. ## Short answer Transmission media are physical paths carrying signals, classified as guided (twisted pair, coaxial, optical fibre) and unguided (radio, microwave, satellite, infrared). Guided media use cables; unguided media use free space. Diagrams show cable cross-sections and wireless links. ## Answer **Transmission media** are the physical paths that carry signals between transmitter and receiver. They are classed as **guided** (wired) and **unguided** (wireless). #### Guided media **1. Twisted pair cable** ```text ~~~/\/\/\/\/\/\/\~~~ two insulated copper ~~~\/\/\/\/\/\/\/~~~ wires twisted together ``` - Two insulated copper wires twisted to reduce crosstalk and noise pickup; UTP and STP types. - Used for telephone subscriber loops, DSL and LAN (Cat-5/6). - Cheap, easy to install; attenuation high at high frequency, limited distance/bandwidth. **2. Coaxial cable** ```text | outer jacket | braid (shield) | insulator | core | ( ( ( ( ● center conductor ) ) ) ) ``` - Central copper conductor, dielectric insulator, outer braided conductor and jacket. - Wider bandwidth and better shielding than twisted pair; used in cable TV, old long-distance FDM trunks, antenna feeders. **3. Optical fibre** ```text cladding ─────────────────────── core ═══> light by total ═══> internal reflection cladding ─────────────────────── ``` - Glass core with higher refractive index than the cladding; light is guided by **total internal reflection**. - Single-mode and multimode types; very low loss (~0.2 dB/km at 1550 nm), huge bandwidth, immune to EMI, light and secure. - Used in backbone, undersea cables, FTTH. #### Unguided media **1. Radio waves (HF/VHF/UHF):** omnidirectional antennas; ground wave, sky wave (HF via ionosphere), line-of-sight; used in broadcasting, mobile, walkie-talkies. **2. Terrestrial microwave (1–40 GHz):** ```text [Dish]))) ─ line of sight ─ (((([Dish] tower repeater every 40-60 km tower ``` Highly directional parabolic dishes on towers; used for long-distance trunks and mobile backhaul; affected by rain and obstacles. **3. Satellite:** ```text [Satellite] ^ \ uplink / v downlink [Earth stn A] [Earth stn B] ``` Geostationary satellite (36,000 km) acts as a repeater in the sky; wide coverage; delay about 250 ms one way. **4. Infrared and light-wave:** short range, line of sight (remote controls, IrDA, free-space optics). | Medium | Bandwidth | Typical use | |---|---|---| | Twisted pair | Low–medium | Local loop, LAN | | Coaxial | Medium | Cable TV | | Optical fibre | Very high | Backbone, FTTH | | Microwave | High | Trunks, backhaul | | Satellite | High | Remote, international | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How does optical fibre guide light? A. Total internal reflection, as the core has a higher refractive index than the cladding B. Reflection from a metal shield C. Radio propagation D. Ground wave Answer: A. Light stays in the higher-index core by total internal reflection. (Key point: Optical fibre principle) 2. Why are the wires of a twisted pair twisted? A. To increase attenuation B. To reduce crosstalk and noise pickup C. To raise bandwidth to Tbps D. To improve light guiding Answer: B. Twisting reduces crosstalk and noise pickup. (Key point: Twisted pair purpose) 3. What is needed for terrestrial microwave over long distances? A. Omnidirectional antennas B. Line-of-sight directional dishes with repeaters every 40-60 km C. Sky-wave reflection D. A twisted pair Answer: B. Microwave is line of sight using parabolic dishes and repeaters, and it is affected by rain. (Key point: Microwave links) 4. What is a typical one-way delay of a geostationary satellite link? A. About 2.5 ms B. About 25 ms C. About 250 ms D. About 25 s Answer: C. GEO at 36,000 km gives roughly 250 ms one-way delay. (Key point: Satellite) ## Related in Telecommunications - [Guided and unguided media for radio signals](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aradio-guided-unguided-compare) β€” Telecommunications, chapter 2 - [Guided vs unguided media; 2-wire to 4-wire](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aguided-unguided-two-four-wire) β€” Telecommunications, chapter 2, asked 2Γ— - [Guided media comparison and hybrid operation](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aguided-media-hybrid-operation) β€” Telecommunications, chapter 2 ## Related in other subjects - [Guided vs unguided transmission media](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aguided-vs-unguided-media) β€” Data Communication, chapter 4 - [Guided and other transmission media](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Atransmission-media-explain) β€” Computer Networks and Security, chapter 2, asked 3Γ— - [Transmission characteristics of guided media](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aguided-media-transmission-characteristics) β€” Data Communication, chapter 4 - [Physical description of guided media](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aguided-media-description) β€” Data Communication, chapter 4, asked 2Γ—