---
title: "Transmission characteristics of guided media"
subject: "Data Communication"
chapter: 4
key: "semester_5/data_communication:guided-media-transmission-characteristics"
source: https://www.bctengineer.com/q/semester_5/data_communication/guided-media-transmission-characteristics
site: BCT Engineering
---

# Transmission characteristics of guided media

Data Communication · Chapter 4: Transmission Media

- Asked in: 2070 Asar, 4 marks
- Video: [CN 5 : Transmission Media | Guided & Unguided Media with Examples](https://www.youtube.com/watch?v=HryzQDpKvwA) — CS & IT Tutorials by Vrushali 👩‍🎓
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/data_communication/guided-media-transmission-characteristics
- Whole chapter: https://www.bctengineer.com/md/semester_5/data_communication/chapter-4

## Question

Briefly describe about transmission characteristics (frequency range, attenuation, delay and repeater spacing) of twisted pair cable, coaxial cable and optical fiber.

## Short answer

Twisted pair: 0-1 MHz, attenuation ~3 dB/km at 1 kHz, delay 5 µs/km, repeater spacing 2 km (UTP supports Gbps up to 100 m). Coaxial cable: 0-500 MHz, attenuation 7 dB/km at 10 MHz, delay 4 µs/km, repeaters every 1-9 km. Optical fibre: 180-370 THz, attenuation 0.2-0.5 dB/km, delay 5 µs/km, repeater spacing up to 40 km.

## Answer

The usual point-to-point transmission characteristics of the three guided media (as in Stallings) are:

| Medium | Frequency range | Attenuation | Delay | Repeater spacing |
|---|---|---|---|---|
| Twisted pair (with loading) | 0-3.5 kHz (analog voice) | 0.2 dB/km at 1 kHz | 50 µs/km | 2 km |
| Twisted pair (multipair cable) | 0-1 MHz | 3 dB/km at 1 kHz | 5 µs/km | 2 km |
| Coaxial cable | 0-500 MHz | 7 dB/km at 10 MHz | 4 µs/km | 1-9 km |
| Optical fibre | 180-370 THz | 0.2-0.5 dB/km | 5 µs/km | 40 km |

- **Twisted pair**: it has a low frequency range and high attenuation, so repeaters or amplifiers are needed about every 2 km. Modern UTP supports Mbps to Gbps over 100 m.
- **Coaxial cable**: the shielded construction gives a wider frequency range and lower attenuation than twisted pair, but attenuation rises quickly with frequency.
- **Optical fibre**: it has the largest frequency range, the lowest attenuation and the greatest repeater spacing, so it suits long-haul links.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which medium has the greatest repeater spacing?
   A. Twisted pair (2 km)
   B. Optical fibre (about 40 km)
   C. Coaxial cable (1-9 km)
   D. All the same
   Answer: B. Fibre has the lowest attenuation. (Key point: Repeater spacing)

2. Frequency range of optical fibre is:
   A. 180-370 THz
   B. 0-500 MHz
   C. 0-1 MHz
   D. 0-3.5 kHz
   Answer: A. Fibre has the widest range. (Key point: Frequency range)

3. How does coax attenuation behave?
   A. Constant with frequency
   B. Lower than fibre
   C. Lower than twisted pair, but grows quickly with frequency
   D. Falls with frequency
   Answer: C. 7 dB/km at 10 MHz and rising with frequency. (Key point: Coax attenuation)

4. Why does twisted pair need repeaters about every 2 km?
   A. It has low delay
   B. It uses light
   C. It is immune to noise
   D. Low frequency range and high attenuation
   Answer: D. Attenuation is high so signals need regenerating. (Key point: Twisted pair)

## Related in Data Communication

- [Optical fiber advantages over coax and twisted pair](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Afiber-advantages) — Data Communication, chapter 4, asked 3×
- [Coaxial cable vs optical fiber](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Acoax-vs-fiber) — Data Communication, chapter 4
- [Optical fiber vs satellite transmission](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aoptical-fiber-vs-satellite) — Data Communication, chapter 4
- [Guided vs unguided transmission media](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aguided-vs-unguided-media) — Data Communication, chapter 4
- [Transmission impairments; attenuation of cable](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aattenuation-cable-numeric) — Data Communication, chapter 1
- [Why wires are twisted in twisted pair](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Atwisted-pair-why-twist) — Data Communication, chapter 4

## Related in other subjects

- [Compare twisted pair, coaxial, fiber](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Acompare-twisted-coax-fiber) — Computer Networks and Security, 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
- [Optical fiber advantages and wireless media](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aoptical-fiber-wireless-media) — Telecommunications, chapter 2
- [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×