Choosing the right Wifi Channel on 2.4Ghz

Choosing the right Wifi Channel on 2.4Ghz

Conventional wisdom dictates that whenever you choose a channel for your 2.4 Ghz Wifi device, you should choose either Channel 1, Channel 6, or Channel 11. According to conventional wisdom, these three channels are the only three channels that do not overlap with another channel in the spectrum, and thus, are the only three that anyone should ever use. You can read more about this conventional wisdom almost anywhere on the internet.

The problem with this conventional wisdom is that, like most pieces of conventional wisdom, it is completely and utterly wrong. It is true that Channels 1, 6, and 11 are the only three channels available in the U.S. that do not overlap with one another. Channel 1 actually uses 2402 to 2422 Ghz, which means that it will interfere with Channel 2 and half of Channel 3. Channel 6 uses 2427 to 2447 Ghz, which means that it uses spectrum from the middle of Channel 4 to the middle of Channel 8. Channel 11 uses 2452 to 2472 Ghz, which means that it uses spectrum from the middle of Channel 9 all the way to what would be Channel 13 (which we don’t use in the U.S.).

So, if you were setting up a network of multiple Wifi Access Points in the middle of the desert, or inside of a lead box, you’d do well to follow the conventional wisdom to prevent one of your devices from interfering with another.

However, it is very likely that you are not setting up a network of multiple Wifi devices inside of a lead box or in the desert. Rather, the chances are good that you are setting up a single Wifi device inside of your home, condo, apartment, or RV. As a result, your 2.4 Ghz network device is competing with a whole host of 2.4 Ghz devices operated by others in adjacent spaces, including baby monitors, cordless telephones, wireless speakers, Bluetooth devices, microwave ovens, 2.4 Ghz wifi devices, and probably a dozen other things that I don’t even know about. Many of these devices use 5 Mhz channel widths (non-overlapping), instead of the 20 Mhz channel width that 802.11 devices use.

So, for example, if Channel 1 is being used by baby monitor that consumes 5 Mhz, and Channel 7 is being used by a cordless phone that consumes 5 Mhz, and channels 10 and 11 are being used by wireless speakers (using a total of 10 Mhz), you’d want to use Channel 4 for your Wifi (which actually utilizes frequencies that compromise the center of Channel 2 through the center of Channel 6, for a total of 20 Mhz). You would most definitely NOT want to use Channels 1, 6, or 11, because all of them would experience interference from the devices that I identified.

Some people wrongly believe that a program like inSSIDer, which shows the other Wifi AP’s in your area and their channels, is a good tool. “Just find the channel that has the least Wifi AP’s with the lowest signals and use it.” Wrong! The problem is that just having another Wifi AP on your channel doesn’t mean that it is going to cause you interference. If the person who set-up that strong AP on Channel 1 never uses it, or only uses it to surf the web, or only uses it while you’re at work or sleeping, you’ll get very little interference from it. On the other hand, if that weaker AP on Channel 11 belongs to someone who streams Netflix at precisely the same time that you intend to do the same, Channel 11 would be a terrible choice, even if there was only ONE AP listed and it was weaker than the rest. The problem with inSSIDER is that it won’t show you the activity on that channel. And inSSIDer won’t show you any of the non-Wifi devices that I discussed above (cordless phones, baby monitors, etc.).

So, how do you choose the right Wifi channel? Well, you can buy a spectrum analyzer and monitor it at various times during the day, but there’s a much simpler method.

Simple. Just follow these four easy rules:

1. Set your channel width to 20 Mhz. 40 Mhz channels spreads your channel size over more than 50% of the entire available 2.4 Ghz spectrum. It increases the risk that interference will slow your speed. And if you’re only using your Wifi to access the internet, a 20 Mhz channel size is more than sufficient to accommodate the speed offered by even the fastest internet available today.

2. If any of your Wifi devices (i.e., your router or your laptop or whatever) will be in the same room as a Microwave oven and you expect it to work while the oven is in use, I strongly recommend Channels 1, 2, 3, or 4. This is because Microwave ovens transmit 1200 watts centered on 2350 Mhz, and spread the signal from roughly Channel 6 to Channel 12. While only 1 watt or so escapes the oven, that is usually more than enough to wipe out the signal transmitted by most wifi laptop cards, which transmit around one tenth of a watt (.1 watt or 100mw). Because of the overlapping nature of Wifi Channels, Channel 4 is the highest channel that you can use that won’t overlap with the interference from a typical microwave oven. If you use Channel 5, roughly 1/3 of your bandwidth will be cut-off. On Channel 6, half will be cut-off. If you don’t mind that your Wifi will go out when you use the microwave, then Channels 5 through 11 are fine.

If you plan to have your Wifi signal pass through a room with a microwave oven, i.e. one device is on one side of the house and the other device is on the other side of the house, and there is a kitchen in between, you should not expect the signal to work when the microwave is on. You’ll need to set-up two APs, one on each side of the room with the microwave. If you only have a few users, you can even put them on the same channel as one another, because when you’re using one, you won’t be using the other. If they’re connected to the same wired network, give them the same SSID and use the same encryption (generally WPA2, AES, with the same key), and your Wifi devices will roam seamlessly between them as you move through the house.

3. Pick any channel at random and use it for a few days. If your throughput is good and you don’t experience random loss of signal, congratulations! You’ve found a good channel. If your throughput is not good or you experience random loss of signal, wait a few days and then pick another channel at random. Continue this process until you’ve tried each channel for a few days.

The best way to test throughput is to test it using the most bandwidth intensive method that you intend to regularly use in the location you intend to use it. So, if you intend to use your Wifi to primarily surf the web in your easy chair, then sit in your easy chair and surf the web. Run a speed test using speedtest.net at different times of day when you might be surfing the web and record the results. Don’t expect to get the same results at different times of the day. If you don’t like the results you get, then change to another channel at random. Once you’ve got a data set for all the channels, pick the best one.

If you plan to use your Wifi primarily for moving large files from your Network Attached Storage device to your laptop, then use that process as a means of testing bandwidth.

Bear in mind that the computer world uses two methods of reporting data speeds: Bytes (B) and bits (b). One Byte is the same as 8 bits. Kilo is a thousand. Mega is a million.

So, for example:

1 KBps (1 thousand bytes per second) is the same as 8 Kbps (8 thousand bits per second).
1 MBps (1 million bytes per second) is the same as 8 Mbps (8 million bits per second).
5 MBps (5 million bytes per second) is the same as 40 MBps (40 million bits per second).

Windows reports file transfer speeds in bytes. Most internet speed tests are reported in bits. So, if your internet speed test shows 26 Mbps and your Windows file transfers are showing 3.25 MBps, they’re actually the same.

Your Wifi device manufacturer advertises its throughput speeds in bits (300 Mbps or 150 Mbps). And Windows will report your link speed in bits. Keep in mind that link speeds are theoretical. Don’t expect to actually get 300 mbps or even 150 mbps. With a 150 Mbps link, you are really only likely to see 40 Mbps (which is equal to about 5 MBps) over the best 2.4 Ghz 20 Mhz channel.

4. Don’t rely upon your device to automatically select a channel for you. While some devices (particularly Ubiquiti’s and Engenius’s) do a pretty good job of automatically selecting a channel, others don’t. However, keep in mind that they auto select the channel at a moment in time. If the device auto selects at 3:00 p.m. in the afternoon, that channel might not be the best channel at 8:45 p.m., when all the new mothers put their children to bed, turn on the baby monitor, and start talking on the cordless, while someone else starts streaming Netflix. The best way to find the right channel is to try all of them over a several day period, and find the one that works best for you where and when you want to use it.

So, there you have it. The best way to pick the right Wifi channel is to pick one at random and try it out. If it doesn’t work, pick another one at random. Repeat until you find the one that works for you.