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Spectrum Reference
Microwave Spectrum Guide: 2.4, 5 & 6 GHz
As operating frequency jumps from sub-1GHz into gigahertz microwave territory, physical behavior changes completely. You trade wall penetration and multi-mile battery reach for massive channel widths (up to 320 MHz) and multi-gigabit throughput. This is the complete channel roster and technical reference for 2.4 GHz, 5 GHz, and 6 GHz.
01 · 2.4 GHz ISM: Complete Channel Roster (Channels 1–14)
The 2.4 GHz ISM band stretches from 2400 to 2483.5 MHz. Standard 2.4 GHz Wi-Fi channels are 20 MHz or 22 MHz wide but spaced only 5 MHz apart, meaning adjacent channels overlap heavily.
In North America under FCC rules, Channels 1, 6, and 11 are the only three non-overlapping 20 MHz channels. Setting an access point to Channel 2, 3, 4, 8, or 9 creates adjacent-channel interference (ACI), raising the noise floor and destroying packet throughput for all nearby nodes.
| Channel | Center Freq | Frequency Span | US (FCC) | Europe (ETSI) | Japan (MIC) | Interference & Application |
|---|---|---|---|---|---|---|
| Ch 1 | 2412 MHz | 2401 – 2423 MHz | Allowed (Standard) | Allowed | Allowed | Primary non-overlapping anchor in US/Global 1/6/11 plan. |
| Ch 2 | 2417 MHz | 2406 – 2428 MHz | Allowed | Allowed | Allowed | Overlaps Ch 1 and Ch 3; causes adjacent-channel interference (ACI). |
| Ch 3 | 2422 MHz | 2411 – 2433 MHz | Allowed | Allowed | Allowed | Overlaps Ch 1, 2, 4, 5. Center of 40 MHz bonded pair (Ch 1+5). |
| Ch 4 | 2427 MHz | 2416 – 2438 MHz | Allowed | Allowed | Allowed | Overlaps Ch 2, 3, 5, 6; bleeds into both Ch 1 and Ch 6 carriers. |
| Ch 5 | 2432 MHz | 2421 – 2443 MHz | Allowed | Allowed | Allowed | Overlaps Ch 3, 4, 6, 7. Heavy bleed into Ch 6 carrier. |
| Ch 6 | 2437 MHz | 2426 – 2448 MHz | Allowed (Standard) | Allowed | Allowed | Primary non-overlapping center anchor in US/Global 1/6/11 plan. |
| Ch 7 | 2442 MHz | 2431 – 2453 MHz | Allowed | Allowed | Allowed | Overlaps Ch 5, 6, 8, 9; close to residential microwave oven peak (2450 MHz). |
| Ch 8 | 2447 MHz | 2436 – 2458 MHz | Allowed | Allowed | Allowed | Overlaps Ch 6, 7, 9, 10; heavily disrupted by microwave oven leakage. |
| Ch 9 | 2452 MHz | 2441 – 2463 MHz | Allowed | Allowed | Allowed | Overlaps Ch 7, 8, 10, 11. Center of 40 MHz bonded pair (Ch 7+11). |
| Ch 10 | 2457 MHz | 2446 – 2468 MHz | Allowed | Allowed | Allowed | Overlaps Ch 8, 9, 11, 12; bleeds directly into Ch 11. |
| Ch 11 | 2462 MHz | 2451 – 2473 MHz | Allowed (Standard) | Allowed | Allowed | Primary non-overlapping upper anchor in US/Global 1/6/11 plan. |
| Ch 12 | 2467 MHz | 2456 – 2478 MHz | Restricted (Low Power) | Allowed | Allowed | Standard in Europe & Japan. FCC Part 15.205 restricts power to prevent 2483.5 MHz bleed. |
| Ch 13 | 2472 MHz | 2461 – 2483 MHz | Restricted (Low Power) | Allowed | Allowed | Standard in Europe (enables 1/5/9/13 4-channel plan). Highly restricted under FCC rules. |
| Ch 14 | 2484 MHz | 2473 – 2495 MHz | Prohibited | Prohibited | Allowed (11b only) | Japan only; restricted strictly to legacy 802.11b DSSS/CCK modulation. Banned everywhere else. |
Who Else Lives in 2.4 GHz?
- Bluetooth LE: 40 channels spaced 2 MHz apart (2402–2480 MHz). The 3 primary advertising channels (37, 38, 39) sit at 2402, 2426, and 2480 MHz — tucked inside the quiet gaps between Wi-Fi Channels 1, 6, and 11.
- Zigbee / Thread / Matter (IEEE 802.15.4): 16 channels numbered 11 to 26. Channels 15, 20, and 25 dodge Wi-Fi carriers; Channel 26 sits safely at 2480 MHz above Wi-Fi Channel 11.
- ESP-NOW: Transmits raw connectionless vendor action frames directly on whatever channel the host ESP32 is tuned to, bypassing AP handshakes.
- Microwave Ovens: Magnetron tubes oscillate around 2450 MHz. Poorly shielded door seals blast hundreds of watts of unsynchronized noise across Channels 8 through 11.
02 · 5 GHz UNII Tiers & Complete Channel Roster (All 25 Channels)
The 5 GHz band (5150 to 5850 MHz) offers 25 separate 20 MHz channels that can be bonded into 40 MHz, 80 MHz, and 160 MHz blocks. The band is segmented into four distinct UNII regulatory tiers:
| UNII Tier | Frequency Span | Channels (20 MHz) | Radar Rules (DFS) | Field Application |
|---|---|---|---|---|
| UNII-1 (Lower) | 5150 – 5250 MHz | 36, 40, 44, 48 (4 channels) | No DFS required | Cleanest indoor band. Zero radar detection; instantly available without scanning delays. |
| UNII-2A (Middle-1) | 5250 – 5350 MHz | 52, 56, 60, 64 (4 channels) | DFS & TPC Mandatory | Shares spectrum with airport weather radar. Radios must listen for 60 seconds before transmitting. |
| UNII-2C / Extended | 5470 – 5725 MHz | 100, 104, 108, 112, 116, 120, 124, 128, 132, 136, 140, 144 (12 channels) | DFS Mandatory (TDWR on 120–128) | Huge swath of channels. Weather radar hits are frequent near airports, triggering channel drops. |
| UNII-3 / ISM (Upper) | 5725 – 5850 MHz | 149, 153, 157, 161, 165 (5 channels) | No DFS required | The undisputed king of outdoor wireless backhauls. High power allowed with directional dish antennas. |
Master 5 GHz Channel Table (Every 20 MHz Channel)
| Channel | Center Freq | UNII Tier | DFS Required? | Max US Power (conducted) | Bonding & Radar Notes |
|---|---|---|---|---|---|
| Ch 36 | 5180 MHz | UNII-1 | No | 1 W (30 dBm) | Lower indoor anchor. Pairs with Ch 40 for 40 MHz (Ch 38); anchor for 80 MHz (Ch 42). |
| Ch 40 | 5200 MHz | UNII-1 | No | 1 W (30 dBm) | Secondary 20 MHz channel in UNII-1 block. |
| Ch 44 | 5220 MHz | UNII-1 | No | 1 W (30 dBm) | Pairs with Ch 48 for 40 MHz (Ch 46). |
| Ch 48 | 5240 MHz | UNII-1 | No | 1 W (30 dBm) | Upper UNII-1 channel. Upper boundary of first 80 MHz block. |
| Ch 52 | 5260 MHz | UNII-2A | Yes (DFS) | 250 mW (24 dBm) | Lower UNII-2A anchor. 60-second CAC quiet scan required. |
| Ch 56 | 5280 MHz | UNII-2A | Yes (DFS) | 250 mW (24 dBm) | Pairs with Ch 52 for 40 MHz (Ch 54). |
| Ch 60 | 5300 MHz | UNII-2A | Yes (DFS) | 250 mW (24 dBm) | Pairs with Ch 64 for 40 MHz (Ch 62). |
| Ch 64 | 5320 MHz | UNII-2A | Yes (DFS) | 250 mW (24 dBm) | Upper UNII-2A channel. Upper boundary of second 80 MHz block (Ch 58). |
| Ch 100 | 5500 MHz | UNII-2C | Yes (DFS) | 250 mW (24 dBm) | Lower UNII-2C Extended anchor. Pairs with Ch 104 for 40 MHz (Ch 102). |
| Ch 104 | 5520 MHz | UNII-2C | Yes (DFS) | 250 mW (24 dBm) | Secondary 20 MHz channel in UNII-2C block. |
| Ch 108 | 5540 MHz | UNII-2C | Yes (DFS) | 250 mW (24 dBm) | Pairs with Ch 112 for 40 MHz (Ch 110). |
| Ch 112 | 5560 MHz | UNII-2C | Yes (DFS) | 250 mW (24 dBm) | Upper boundary of third 80 MHz block (Ch 106). |
| Ch 116 | 5580 MHz | UNII-2C | Yes (DFS) | 250 mW (24 dBm) | Lower boundary of airport Terminal Doppler Weather Radar (TDWR) band. |
| Ch 120 | 5600 MHz | UNII-2C | Yes (TDWR Radar) | 250 mW (24 dBm) | TDWR weather radar core. Requires 10-minute CAC quiet listening period in many regions. |
| Ch 124 | 5620 MHz | UNII-2C | Yes (TDWR Radar) | 250 mW (24 dBm) | TDWR weather radar core. Frequent radar strikes trigger automatic channel drops. |
| Ch 128 | 5640 MHz | UNII-2C | Yes (TDWR Radar) | 250 mW (24 dBm) | TDWR weather radar core. High risk of 60-second channel vacations. |
| Ch 132 | 5660 MHz | UNII-2C | Yes (DFS) | 250 mW (24 dBm) | Pairs with Ch 136 for 40 MHz (Ch 134). |
| Ch 136 | 5680 MHz | UNII-2C | Yes (DFS) | 250 mW (24 dBm) | Secondary 20 MHz channel in UNII-2C block. |
| Ch 140 | 5700 MHz | UNII-2C | Yes (DFS) | 250 mW (24 dBm) | Pairs with Ch 144 for 40 MHz (Ch 142). |
| Ch 144 | 5720 MHz | UNII-2C | Yes (DFS) | 250 mW (24 dBm) | Added by FCC in 2014; spans the boundary between UNII-2C and UNII-3. |
| Ch 149 | 5745 MHz | UNII-3 | No | 1 W (30 dBm) | Lower UNII-3 / ISM anchor. Pairs with Ch 153 for 40 MHz (Ch 151). |
| Ch 153 | 5765 MHz | UNII-3 | No | 1 W (30 dBm) | Secondary 20 MHz channel in UNII-3 block. |
| Ch 157 | 5785 MHz | UNII-3 | No | 1 W (30 dBm) | Center UNII-3 channel. Pairs with Ch 161 for 40 MHz (Ch 159). |
| Ch 161 | 5805 MHz | UNII-3 | No | 1 W (30 dBm) | Secondary 20 MHz channel in UNII-3 block. |
| Ch 165 | 5825 MHz | UNII-3 | No | 1 W (30 dBm) | Upper 20 MHz limit in US UNII-3. 20 MHz only (cannot bond to 40 MHz in standard plan). |
The DFS Radar Drop Trap
Dynamic Frequency Selection (DFS) is legally required on UNII-2 channels. If an access point detects a radar pattern (such as an airport weather radar sweeping the horizon), it must silence transmission within 200 ms and vacate the channel for 60 seconds. On TDWR channels (120, 124, 128), a 10-minute Channel Availability Check (CAC) is required before transmitting. For critical field links, stick to UNII-1 (36–48) or UNII-3 (149–165).
03 · 6 GHz Wi-Fi 6E & 7: UNII Tiers & Preferred Scanning Channels
The 6 GHz band (5925 to 7125 MHz) opened up an astonishing 1200 MHz of clean spectrum. It contains 59 20-MHz channels, 29 40-MHz channels, 14 80-MHz channels, 7 160-MHz channels, and 3 massive 320-MHz channels in Wi-Fi 7.
| UNII Tier | Frequency Span | Total Bandwidth | 20 MHz Ch Count | Preferred Scanning Channels (PSCs) | AFC / Regulatory Rules |
|---|---|---|---|---|---|
| UNII-5 | 5925 – 6425 MHz | 500 MHz | 24 channels | 6 PSCs (5, 21, 37, 53, 69, 85) | Permitted for Low Power Indoor (LPI) and Standard Power (with AFC). |
| UNII-6 | 6425 – 6525 MHz | 100 MHz | 5 channels | 1 PSC (101) | Indoor-only LPI in US; shares spectrum with mobile TV pickup links. |
| UNII-7 | 6525 – 6875 MHz | 350 MHz | 17 channels | 5 PSCs (117, 133, 149, 165, 181) | Permitted for LPI and Standard Power (with AFC outdoor coordination). |
| UNII-8 | 6875 – 7125 MHz | 250 MHz | 13 channels | 3 PSCs (197, 213, 229) | Indoor-only LPI in US; shares spectrum with fixed microwave links. |
Preferred Scanning Channels (PSC) Roster
Because scanning 59 separate 20 MHz channels would drain client device batteries, Wi-Fi 6E/7 defines Preferred Scanning Channels (PSCs) spaced every 80 MHz. Client devices only scan these exact 14 channels during active discovery:
| PSC Channel | Center Freq | UNII Tier | Corresponding 80 MHz Block | Corresponding 160 MHz Block |
|---|---|---|---|---|
| Ch 5 | 5975 MHz | UNII-5 | Ch 7 (5945 – 6025 MHz) | Ch 15 (5945 – 6105 MHz) |
| Ch 21 | 6055 MHz | UNII-5 | Ch 23 (6025 – 6105 MHz) | Ch 15 (5945 – 6105 MHz) |
| Ch 37 | 6135 MHz | UNII-5 | Ch 39 (6105 – 6185 MHz) | Ch 47 (6105 – 6265 MHz) |
| Ch 53 | 6215 MHz | UNII-5 | Ch 55 (6185 – 6265 MHz) | Ch 47 (6105 – 6265 MHz) |
| Ch 69 | 6295 MHz | UNII-5 | Ch 71 (6265 – 6345 MHz) | Ch 79 (6265 – 6425 MHz) |
| Ch 85 | 6375 MHz | UNII-5 | Ch 87 (6345 – 6425 MHz) | Ch 79 (6265 – 6425 MHz) |
| Ch 101 | 6455 MHz | UNII-6 | Ch 103 (6425 – 6505 MHz) | Ch 111 (6425 – 6585 MHz) |
| Ch 117 | 6535 MHz | UNII-7 | Ch 119 (6505 – 6585 MHz) | Ch 111 (6425 – 6585 MHz) |
| Ch 133 | 6615 MHz | UNII-7 | Ch 135 (6585 – 6665 MHz) | Ch 143 (6585 – 6745 MHz) |
| Ch 149 | 6695 MHz | UNII-7 | Ch 151 (6665 – 6745 MHz) | Ch 143 (6585 – 6745 MHz) |
| Ch 165 | 6775 MHz | UNII-7 | Ch 167 (6745 – 6825 MHz) | Ch 175 (6745 – 6905 MHz) |
| Ch 181 | 6855 MHz | UNII-7 | Ch 183 (6825 – 6905 MHz) | Ch 175 (6745 – 6905 MHz) |
| Ch 197 | 6935 MHz | UNII-8 | Ch 199 (6905 – 6985 MHz) | Ch 207 (6905 – 7065 MHz) |
| Ch 213 | 7015 MHz | UNII-8 | Ch 215 (6985 – 7065 MHz) | Ch 207 (6905 – 7065 MHz) |
| Ch 229 | 7095 MHz | UNII-8 | Ch 231 (7065 – 7125 MHz) | 20/40/80 MHz only |
04 · Propagation Physics & Free Space Path Loss
Free Space Path Loss follows the inverse square law and frequency scaling:
FSPL (dB) = 20·log10(distance) + 20·log10(frequency) + 32.44
Every time frequency doubles, path loss increases by 6 dB:
- 915 MHz vs 2.4 GHz: 2.4 GHz suffers 8.5 dB more path loss over the same line-of-sight distance.
- 915 MHz vs 6 GHz: 6 GHz suffers 16.3 dB more path loss.
- Drywall & Glass: While 915 MHz passes through three interior sheetrock walls with ~3 dB attenuation, a single 6 GHz wave loses 6 to 10 dB per wall. 6 GHz is strictly an in-room or pure line-of-sight technology.