Describe data transmission methods (fibre optic, wireless)
📡 14 Communications Technology – Data Transmission Methods
Fibre Optic Transmission
Think of fibre optic cables as a super‑fast highway for light. Instead of sending electric signals like a car, we send pulses of light through glass or plastic strands. The light travels at about 200 000 km/s (≈2/3 the speed of light in a vacuum), making fibre optic the fastest way to move data over long distances.
🔍 Key points:
- Uses total internal reflection to keep light inside the core.
- Can carry data at gigabit per second (Gbps) rates.
- Low attenuation: signals lose very little strength over 100 km.
- Immune to electromagnetic interference (EMI).
📐 Speed calculation example: If a data packet travels 100 km in 0.5 ms, its speed is:
$ \frac{100\,\text{km}}{0.5\,\text{ms}} = 200\,000\,\text{km/s} $
| Feature | Pros | Cons |
|---|---|---|
| Bandwidth | Very high | Expensive to install |
| Signal loss | Low over long distances | Sensitive to bending |
| Security | High | Hard to tap |
Wireless Transmission
Wireless is like sending messages through the air using radio waves. Think of shouting across a field – the sound travels through the air to reach the listener. In technology, we use microwaves, radio waves, or infrared to carry data without cables.
🔍 Key points:
- Uses modulation to encode data onto carrier waves.
- Speed varies: Wi‑Fi can reach up to 1 Gbps, but real‑world speeds are lower.
- Susceptible to interference from other devices and obstacles.
- Convenient for mobile devices and IoT.
📐 Signal strength example: Received power $P_r$ can be calculated using the Friis transmission equation:
$ P_r = P_t G_t G_r \left( \frac{\lambda}{4\pi d} \right)^2 $
Where $P_t$ is transmitted power, $G_t$ and $G_r$ are antenna gains, $\lambda$ is wavelength, and $d$ is distance.
| Aspect | Advantages | Limitations |
|---|---|---|
| Installation | Fast, no cables | Requires line‑of‑sight |
| Mobility | High | Signal drops indoors |
| Security | Encryption available | Can be intercepted |
Exam Tips for Data Transmission Methods
- Remember the speed of light in fibre (~200 000 km/s) and how it compares to wireless speeds.
- Use the Friis equation when asked about wireless signal strength.
- List advantages and disadvantages of each method in a table format for quick recall.
- Explain the concept of total internal reflection for fibre and modulation for wireless.
- Include real‑world examples: Internet backbone uses fibre, Wi‑Fi for home networks.
Revision
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