The electromagnetic spectrum is divided into frequency bands, each allocated for specific uses — from submarine communication at a few hertz to millimeter-wave 5G at tens of gigahertz. Understanding frequency bands is essential for anyone working with wireless technology.
The Frequency Spectrum
- ELF (3–30 Hz): Submarine communication. Extremely low data rate but penetrates seawater.
- MF (300 kHz–3 MHz): AM radio (530–1,700 kHz). Ground-wave propagation during day, skywave at night.
- HF (3–30 MHz): Shortwave radio, amateur radio, aviation. Bounces off the ionosphere for global reach.
- VHF (30–300 MHz): FM radio (88–108 MHz), air traffic control, marine VHF.
- UHF (300 MHz–3 GHz): TV, GPS (1.575 GHz), Wi-Fi (2.4 GHz), Bluetooth, 4G/5G.
- SHF (3–30 GHz): Wi-Fi 5 GHz/6E, radar, satellite, 5G mmWave (24–40 GHz).
- EHF (30–300 GHz): Emerging 6G research, automotive radar (77 GHz), security scanners.
Wi-Fi Frequency Bands
2.4 GHz (2,400–2,483 MHz): Long range, good wall penetration, but crowded (Bluetooth, microwaves, baby monitors share this band). Channels: 1–14 (11 in US). Non-overlapping: 1, 6, 11.
5 GHz (5,150–5,825 MHz): Faster speeds, less congestion, shorter range. More channels available. Required for 802.11ac/ax.
6 GHz (5,925–7,125 MHz): Wi-Fi 6E. Up to 1,200 MHz of new spectrum. Very fast, very short range. No legacy device interference.
Frequency Conversion for RF Work
Wavelength = speed of light ÷ frequency. At 2.4 GHz: λ = 3×10⁸ ÷ 2.4×10⁹ = 0.125 m = 12.5 cm. At 5 GHz: λ = 6 cm. Antenna size is related to wavelength — higher frequencies need smaller antennas.
For RF engineers: 1 GHz = 1,000 MHz = 1,000,000 kHz. A signal at 900 MHz is 0.9 GHz. The 5G n78 band at 3,500 MHz is 3.5 GHz.
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