5 GHz Wi-Fi Guide: 802.11ac/ax, DFS Channels & Diagnostics

Core Technical Specifications

center Freq 5.150–5.850 GHz (UNII-1 through UNII-3)

modulation OFDM / OFDMA (Wi-Fi 6)

data Encoding 64-QAM (11a), 256-QAM (11ac), 1024-QAM (11ax)

operating Range 15–50 m indoor

antenna PCB trace, ceramic, or external dual-band dipole

tx Power ≤ 200 mW EIRP (EU UNII-1) / ≤ 1 W (US)

bandwidth 20 / 40 / 80 / 160 MHz

channel Spacing 20 MHz base, non-overlapping

Real-World Devices & Applications

Networking

High-performance routers and access points
Mesh systems (backhaul uses 5 GHz)
FPV drone video links (5.8 GHz)
Wireless bridges and point-to-point links

Reference Circuits & Schematics

Dual-Band Wi-Fi Architecture

Modern dual-band routers use separate radio chains for 2.4 GHz and 5 GHz, enabling simultaneous operation.

Pin	Description
`5 GHz Radio`	Dedicated 5 GHz radio chain with PA
`2.4 GHz Radio`	Legacy/IoT 2.4 GHz support
`Ethernet WAN`	Uplink to ISP router or modem
`Ethernet LAN`	Wired client ports

Circuit Walk-Through

5 GHz offers more bandwidth (up to 160 MHz channels) and less interference but shorter range due to higher path loss. DFS channels (52–144) require 60s radar detection scan before TX and must vacate within 10s if radar detected.

Signal Structure & Waveform Analysis

5 GHz UNII Band Layout

Divided into UNII sub-bands with different power limits and DFS requirements.

UNII-1 (36–48)

5.150–5.250 GHz

Indoor only, no DFS

UNII-2 (52–64)

5.250–5.350 GHz

DFS required

UNII-2e (100–144)

5.470–5.725 GHz

DFS required, widest range

UNII-3 (149–165)

5.725–5.850 GHz

No DFS, highest power

Timing Notes: DFS: 60s CAC before TX, 10s channel vacate on radar, 30min non-occupancy period.

Analysis & Capture Tips

Wi-Fi Analyser for 5 GHz channel occupancy
Check AP DFS event logs for radar detections
Verify 80/160 MHz width achievable without overlap

Bench Troubleshooting & Repair Guide

1. DFS Channel Drops

AP admin console / syslog

AP suddenly switches channels = DFS radar event. False triggers from weather radar or faulty hardware. Move to non-DFS channels (36–48 or 149–165) for stability.

2. Range Limitations

Ekahau / NetSpot

5 GHz has ~6 dB more path loss than 2.4 GHz, worse wall penetration. Use heatmap tool to verify coverage.

3. Client Compatibility

AP client list / device specs

Older/IoT devices may not support 5 GHz. Check client capabilities. Ensure band steering is configured correctly.

5 GHz Wi-Fi