WiFi 20 MHz or 40 MHz: how to choose the bandwidth

Buy new WiFi router we will often find the words «300 Mbps«, Speed ​​that is obtained with the WiFi connection on the 2,4 GHz frequency. However, once the device is installed, we find that the connection speed is much lower, especially on desktops with wireless adapters . What users do not know is that to obtain this speed it is necessary to act on the router and configure the Band Width item (in some routers also called Band Width, WiFi Bands or WiFi 20 MHz or 40 MHz).

In this guide we will discover what does WiFi 20 MHz or 40 MHz mean and how to configure the wireless network; We will discover that maximum speed is not always the best path to a stable connection.

WiFi 20 MHz or 40 MHz

Question of channels

If you have read our previous guide on 2,4 GHz and 5 GHz WiFi networks, you will know that, given a specific frequency, there will be a variety of channels available for wireless data transmission.

These channels are indicated by a number:

• In the 2,4 GHz frequency the authorized channels for Italy are 13 (from 1 to 13)
• In the 5 GHz frequency, there are 19 authorized channels for Italy, many of them only at low power (many channels are prohibited)

Each channel has its own "Width" indicating the amount of data that can be transmitted within that particular channel. Therefore, it follows that:

• Larger channel = much more data to carry wirelessly

Thus, using a router that operates on the 2,4 GHz frequency with the N protocol (the fastest on this frequency) we will have the following scenario.

• 13 channels of 22 MHz each (rounded to 20 MHz on routers for convenience)
• Channel 14 is not authorized in Italy (only available in Japan)
• Maximum transmission speed 144,5 Mbps

Many routers configure the channel at 20 MHz by default, so we will obtain a maximum speed of 144,5 Mbps (on compatible devices). To reach 300 Mbps we will have to "fatten" the channel.

The 40 MHz channel

The IEEE standard states that two "merged" channels can only be used under special network conditions. In this way Doubling the channel width to 40 MHz will allow us to take advantage of the 300 Mbps announced in the package.

40 MHz problems

Expanding the channel means double interference with neighboring networks. To remedy this, the IEEE introduced a 2,4 GHz coexistence mechanism to avoid nuisance to neighboring networks.

Many router manufacturers have adapted to the standard, so they do not allow users to arbitrarily select 40 MHz, but rather limit themselves to "Auto 20/40". Therefore, if you have the entry «Auto 20/40», the router will only use 40 MHz if the neighboring channels only «free»otherwise it will use 20 MHz so as not to harm the neighbors.

Some manufacturers have not fully adhered to the coexistence mechanism, and allow the user to choose the 40 MHz channel regardless of network conditions.

What to choose?

Given how congested 2,4 GHz networks are. using 40 MHz without having problems of interference and signal drops. it is utopian. There will be very few times that you take advantage of the 300 Mbps.

So in 2,4 GHz frequencies I always recommend using the 20 MHz channels. If you have interference, better change the channel.

If you don't fix the interference problems, it's time to go for a new router.