--- title: "Guided and unguided media for radio signals" subject: "Telecommunications" chapter: 2 key: "semester_8/telecommunications:radio-guided-unguided-compare" source: https://www.bctengineer.com/q/semester_8/telecommunications/radio-guided-unguided-compare site: BCT Engineering --- # Guided and unguided media for radio signals Telecommunications · Chapter 2: Transmission Media - Asked in: 2072 Kartik, 10 marks - Video: [Guided Vs Unguided Transmission Media | Differences & Comparison | Types of Transmission Media](https://www.youtube.com/watch?v=vUDtFjiNib4) — About Technology - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/telecommunications/radio-guided-unguided-compare - Whole chapter: https://www.bctengineer.com/md/semester_8/telecommunications/chapter-2 ## Question In case of transmission media of radio signal what are guided and unguided media? Compare them also. ## Short answer Guided media confine radio signals along a conductor (twisted pair, coax) or fibre/waveguide; unguided media radiate electromagnetic waves through free space via antennas (ground wave, sky wave, space wave, satellite). Guided offers higher security, less interference, and attenuation per km, while unguided supports mobility and is easier over difficult terrain but faces shared spectrum and fading. ## Answer A **transmission medium** is the physical path between transmitter and receiver. For a radio-frequency (RF) signal it can be **guided**, where the wave is confined and directed by a physical structure (wire, cable, fibre or waveguide), or **unguided**, where the electromagnetic wave travels through free space (air, vacuum, sea water) radiated by an antenna. #### Guided media The wave travels along a conductor or dielectric that sets its path. - **Twisted pair** – two insulated copper wires twisted together to cancel interference; used for telephone loops and LANs (up to about 100 MHz for Cat-5e and 250 MHz for Cat-6). - **Coaxial cable** – centre conductor, dielectric, braided shield; 50 Ω or 75 Ω; carries RF up to a few GHz (cable TV, antenna feeders, old trunk carrier). - **Optical fibre** – light guided by total internal reflection in a glass core; very large bandwidth and low loss (≈0.2 dB/km at 1550 nm). - **Waveguide** – hollow metal tube carrying microwaves between radar/microwave equipment and the antenna. #### Unguided media The antenna launches an electromagnetic wave which propagates as: - **Ground wave** (LF/MF, follows the earth's surface, AM broadcast) - **Sky wave** (HF, reflected by the ionosphere, long-distance radio) - **Space / line-of-sight wave** (VHF and above: FM, TV, terrestrial microwave, mobile) - **Satellite links** (uplink/downlink via a geostationary or LEO satellite) - **Infrared / free-space optics** (short range, line of sight) ```text Guided: Tx ===== cable / fibre ===== Rx Unguided: Tx Rx | ~ ~ ~ free space ~ ~ ~ | /_\ (antenna) /_\ ``` #### Comparison | Point | Guided media | Unguided media | |---|---|---| | Path | Physical conductor or fibre | Free space via antennas | | Direction | Signal confined, point-to-point | Broadcast or directional beam | | Installation | Cable laying, right of way needed | Only towers/antennas at ends | | Cost with distance | Rises with route length | Mostly fixed (terminals) | | Attenuation | Exponential with length (dB/km) | Spreading loss $\propto d^2$, rain/fog fade | | Interference | Low (shielding, twisting, fibre immune) | High; shared spectrum, fading, multipath | | Security | Better; must tap the cable | Poorer; easy to intercept | | Bandwidth | Very high for fibre | Limited by spectrum licence | | Mobility | None | Supports mobile users | | Terrain | Hard across rivers, mountains | Easy over difficult terrain | | Examples | Twisted pair, coax, fibre | Microwave, satellite, cellular, Wi-Fi | #### Choice in practice Guided media are preferred for high-capacity, stable backbone links in cities (fibre between exchanges). Unguided media suit mobile users, rural and mountainous areas (very common in Nepal, e.g. microwave and VSAT links to remote districts), quick deployment and broadcasting. Modern networks combine both: a fibre backbone plus radio access. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What distinguishes guided from unguided media? A. Guided uses antennas; unguided uses cables B. Guided confines the wave to a physical structure; unguided radiates through free space C. Guided is always digital D. Unguided has no attenuation Answer: B. Guided: wire, cable, fibre, waveguide. Unguided: antenna-launched waves in free space. (Key point: Guided vs unguided) 2. How does attenuation behave in the two kinds of media? A. Guided: spreading loss ~ d^2; unguided: exponential in dB/km B. Both are independent of distance C. Both follow d^2 D. Guided: exponential with length (dB/km); unguided: spreading loss ~ d^2 plus rain/fog Answer: D. Cable loss is in dB/km; free-space loss spreads with distance squared. (Key point: Attenuation laws) 3. Which comparison is correct? A. Guided supports mobile users; unguided is more secure B. Both are equally easy to intercept C. Unguided supports mobility and is easier to intercept; guided is more secure but fixed D. Unguided cannot cross rivers or mountains Answer: C. Wireless allows mobility and easy terrain crossing but is easy to intercept. (Key point: Security and mobility) 4. Which is the typical choice in practice? A. Fibre for city backbones; radio for mobile users and remote or mountainous areas B. Radio only for backbones C. Fibre for mobile users D. Cable for remote Himalayan districts Answer: A. Modern networks combine a fibre backbone with radio access. (Key point: Choice in practice) ## Related in Telecommunications - [Guided and unguided transmission media](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Atransmission-media-explain) — Telecommunications, chapter 2, asked 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) — Telecommunications, chapter 2, asked 2× - [Guided media comparison and hybrid operation](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aguided-media-hybrid-operation) — Telecommunications, chapter 2 - [Radio signal in twisted pair and coaxial cable](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aradio-signal-twisted-coaxial) — 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) — 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) — Computer Networks and Security, chapter 2, asked 3× - [Transmission characteristics of guided media](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aguided-media-transmission-characteristics) — Data Communication, chapter 4 - [Physical description of guided media](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aguided-media-description) — Data Communication, chapter 4, asked 2×