Wireless Transmission Media: Radio, Microwave, Infrared, and Satellite Communication
Unguided Media (also called Wireless Media) transports electromagnetic waves through the air or vacuum without using physical conductors or cables.
1. The 3 Primary Wireless Frequency Bands
The Three Main Wireless Bands
📻 1. Radio Waves (3 kHz - 1 GHz)
Omnidirectional; penetrates walls easily; used in FM radio, AM radio & cellular
📡 2. Microwaves (1 GHz - 300 GHz)
Unidirectional line-of-sight; cannot pass walls; used in radar & satellite links
🔴 3. Infrared (300 GHz - 400 THz)
Short-range; blocked by solid obstacles; used in TV remote controls
Understanding the 3 Types:
1. Radio Waves (Omnidirectional)
- Signals propagate in all directions simultaneously from the transmitting antenna.
- Key Advantage: Penetrates through building walls and obstacles easily. The receiving antenna does not need to be physically aligned with the transmitter.
- Applications: FM/AM radio broadcasts, police wireless walkie-talkies, cellular mobile towers.
2. Terrestrial Microwave (Unidirectional Line-of-Sight)
- Highly directional focused electromagnetic beams.
- Requirement: Transmitting and receiving dish antennas must be mounted on tall towers pointing directly at each other (Line of Sight - LoS) with zero mountain or building obstructions.
- Applications: Long-distance phone trunk lines between hilltops, mobile tower backhaul.
3. Infrared Waves (Short-Range)
- Cannot pass through solid walls or doors.
- Advantage: High security with zero interference from neighboring rooms.
- Applications: TV remote controls, wireless optical computer mice, short-range indoor sensors.
2. Satellite Communication
A communication satellite is essentially a massive repeater in outer space. It receives signals from an Earth ground station on an Uplink frequency, amplifies them, and transmits them back to another part of Earth on a Downlink frequency using an electronic device called a Transponder.
The Three Satellite Orbit Types:
| Orbit Type | Altitude Above Earth | Orbital Period | Real-World Applications |
|---|---|---|---|
| GEO (Geostationary Orbit) | Exactly 35,786 km directly above the equator | Exactly 24 hours (Appears completely stationary in the sky) | Tata Play / Dish TV DTH, weather forecasting (INSAT). |
| MEO (Medium Earth Orbit) | 2,000 km to 20,000 km | 6 to 12 hours | GPS (Global Positioning System) navigation, GLONASS. |
| LEO (Low Earth Orbit) | 500 km to 1,500 km | ~90 minutes (Ultra-low latency ~25ms) | High-speed satellite internet (Starlink, OneWeb). |
💡 DAVV Exam Tip
Question (10 Marks): “Explain wireless transmission media. Differentiate between Radio waves, Microwaves, and Infrared. What are GEO and LEO satellites?”
- Compare Omnidirectional (Radio) vs Line-of-Sight (Microwave) vs Short-range (Infrared).
- Give the exact GEO altitude: 35,786 km.
- Mention Starlink as a modern example of LEO satellite internet.