📘 06-02: Frequencies, Channels & Antennas¶
📌 The Two Main Bands¶
| 2.4 GHz | 5 GHz | |
|---|---|---|
| Range | Longer, better penetration | Shorter |
| Speed | Lower | Higher |
| Channels | Few (crowded) | Many (cleaner) |
| Interference | High (microwaves, Bluetooth, cordless phones) | Lower |
Wi-Fi 6E adds the 6 GHz band for even more clean spectrum.
📌 Channels¶
- In 2.4 GHz, the only non-overlapping 20 MHz channels are 1, 6, and 11. Using others causes co-channel/adjacent-channel interference.
- 5 GHz has many non-overlapping channels, allowing more APs and wider (channel-bonded) channels.
🔹 Channel bonding¶
Combining channels (40/80/160 MHz) increases speed but consumes more spectrum — practical mainly in 5/6 GHz; it worsens congestion in 2.4 GHz.
📌 Antennas¶
| Type | Pattern | Use |
|---|---|---|
| Omnidirectional | All directions | General coverage |
| Directional (Yagi, panel, parabolic) | Focused beam | Point-to-point links, extended range |
Higher gain = more focused/farther signal.
📌 Signal Quality¶
- RSSI — received signal strength.
- SNR (signal-to-noise ratio) — higher is better; low SNR forces lower data rates, retransmissions, and drops.
- Signal weakens with distance (path loss) and is absorbed/reflected by walls and objects.
Tip
Key idea — 2.4 GHz = range but crowded (use channels 1/6/11); 5/6 GHz = speed and clean channels. Use directional antennas for point-to-point, and design for good SNR.
See also: Wireless Fundamentals & 802.11 Standards, Wireless Design & Roaming
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