- 2072 Kartik · 10 marks
Guided and unguided media for radio signals
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.
In case of transmission media of radio signal what are guided and unguided media? Compare them also.
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)
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 , 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.
✓ Answer checked by Claude Opus 5.5 (high effort)
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