When home Wi-Fi stutters, the temptation is to buy a new router. Very often, though, the problem is not the device but the channel it transmits on. In an apartment block dozens of networks share the same slice of spectrum, and if they all shout on the same frequency, none of them is heard well. Understanding how channels work lets you recover performance without spending anything.
How a channel works
Wi-Fi is a shared medium: on a given channel only one device can transmit at a time. The others listen, wait for the channel to be free and only then speak. This mechanism also applies to neighbours' networks using the same channel: they do not "steal" bandwidth directly, but they make each other wait. The more active devices there are on the same channel, the more time is spent queuing.
There are two different kinds of disturbance:
- Co-channel interference: networks on the same channel. It is manageable, because devices coordinate and take turns.
- Adjacent-channel interference: networks on partially overlapping channels. It is worse, because devices do not recognise each other as decodable Wi-Fi and only perceive noise, which degrades the signal.
This leads to a counter-intuitive principle: it is better to share exactly one channel with a neighbour than to sit halfway between two busy channels.
The 2.4 GHz band
On 2.4 GHz channels are spaced 5 MHz apart but each one occupies about 20 MHz, so they overlap. The only channels that do not touch are 1, 6 and 11. In Europe channels 12 and 13 are also available, but some devices configured for other markets cannot see them: using them can make the network disappear from an old laptop or a smart appliance.
The practical rules for this band are simple:
- Choose only among 1, 6 and 11.
- Set the width to 20 MHz. 40 MHz on 2.4 GHz takes up almost half the band and makes things worse for everyone, you included.
- Reserve this band for distant devices or those that support nothing else, such as smart plugs and sensors.
The advantage of 2.4 GHz is range; the drawback is limited capacity and the presence of other sources, such as microwave ovens and Bluetooth devices.
The 5 GHz band
On 5 GHz there is much more room and 20 MHz channels do not overlap. Here the reasoning changes: several channels can be bonded to obtain widths of 40, 80 or 160 MHz and therefore higher speeds.
| Width | Advantage | Drawback |
|---|---|---|
| 20 MHz | Maximum robustness, many free channels | Lower peak speed |
| 40 MHz | Good compromise in apartment blocks | Fewer channels available |
| 80 MHz | High speeds, standard for Wi-Fi 5 and 6 | Greater chance of overlap |
| 160 MHz | Top speeds at short range | Few free blocks, often on DFS |
In an apartment surrounded by other networks, 80 MHz is usually the balance point. 160 MHz performs well in an isolated house, much less so in a crowded building.
DFS channels
Part of the 5 GHz band is shared with weather radar and other radar systems. On these channels, called DFS (Dynamic Frequency Selection), the router must listen before transmitting and, if it detects radar, must leave the channel. This has two practical effects: at power-on the network may appear with a delay of about a minute, and in rare cases the network suddenly changes channel, with a brief disconnection.
DFS channels are often the freest precisely because many routers avoid them. If you live far from airports or radar stations, trying them is a good idea; if you notice periodic disconnections, go back to the non-DFS channels in the lower part of the band.
Reading a scan
Before choosing, you need to observe. On a laptop or an Android smartphone you can use Wi-Fi analysis apps that show visible networks, channel, width and signal strength. On Linux a single command is enough:
nmcli -f SSID,CHAN,SIGNAL,RATE dev wifi list
What to look at:
- The number of networks per channel matters less than their strength. Ten distant networks at -85 dBm cause little disturbance; a single network at -55 dBm on the same channel causes a lot.
- Scan from the rooms where you use the network, not next to the router. What matters is where the device is.
- Repeat the measurement in the evening, when neighbours are home and networks are busier.
Automatic or manual selection
Almost all routers offer automatic channel selection. It works reasonably well, but often relies on a scan made at boot and is never refreshed. In my work I prefer a reasoned manual choice on the 2.4 GHz band, where there are only three options, and I leave automatic mode on 5 GHz only if the router re-evaluates it periodically.
If you have a mesh system or several access points, assign different channels to units close to each other, so they do not compete for the same radio space.
In short
- On 2.4 GHz use only channels 1, 6 or 11 with a 20 MHz width.
- On 5 GHz, 80 MHz is the most common compromise; 160 MHz only where the spectrum is free.
- DFS channels are often free, but can cause delays and sudden changes.
- Assess the strength of nearby networks, measuring where you actually use Wi-Fi.
- Sharing a channel is better than overlapping halfway between two.
