Electromagnetic Spectrum Overview

Study Notes

Ultraviolet light, X-rays, and gamma rays have higher frequencies but are challenging to produce, modulate, and are harmful to living organisms.
The ITU nomenclature classifies frequencies: LF (Low Frequency) from 30 kHz to 300 kHz, MF (Medium Frequency), and HF (High Frequency).
Bands above 10 MHz are categorized as Very, Ultra, Super, Extremely, and Tremendously High Frequency; additional terms include Incredibly, Astonishingly, and Prodigiously High Frequency (IHF, AHF, PHF).

The capacity of electromagnetic waves to carry information is linked to both received power and bandwidth, making fiber optics favorable for networking due to their high bandwidth capabilities.

Radio waves are easily generated, travel long distances, penetrate buildings, and transmit omnidirectionally, eliminating the need for precise alignment between transmitter and receiver.
VLF, LF, and MF bands allow radio waves to follow the earth's contours, with effective detection possible up to 1000 km at lower frequencies; commonly used in AM radio broadcasting.

In HF and VHF bands, ground waves are absorbed, but waves reaching the ionosphere reflect back to Earth, enhancing communication range.

Microwaves, operating above 100 MHz, travel in straight lines and can be focused using parabolic antennas which increase the signal-to-noise ratio.
Effective communication requires precise alignment of transmitting and receiving antennas, allowing multiple transmitters to communicate with multiple receivers without interference when spacing is managed.

Due to the straight-line path of microwaves, repeaters are necessary for long distances; the spacing between repeaters can increase with tower height (e.g., 100-meter towers can be spaced 80 km apart).

Microwaves range from 1 GHz (30 cm) to 12 GHz (1 mm) and are categorized into bands such as L, S, C, and X.
Common uses include satellite communications, cellular networks, Bluetooth, Wi-Fi, and GPS.
Microwave propagation can face challenges due to obstacles and atmospheric conditions, leading to multipath fading where delayed waves arrive out of phase, potentially canceling signals.

At frequencies around 4 GHz, microwaves are absorbed by water, particularly during rainfall, which may necessitate rerouting communication links to avoid interruptions.

Unguided optical signaling has historical applications and modern uses include connecting Local Area Networks (LANs) through rooftop lasers.
Laser-based signaling is unidirectional, necessitating separate lasers and photodetectors at each end, offering high bandwidth and security.

Satellites act as relay stations, receiving signals on one frequency, amplifying them, and retransmitting on another; they are classified based on orbital altitude:
- Geostationary Orbit Satellites (GEO)
- Medium-Earth Orbit Satellites (MEO)
- Low-Earth Orbit Satellites (LEO)
Applications of satellites include television broadcasting, long-distance telephony, and private business networks.