For a while, it seemed that Wi-Fi was becoming a victim of its own success. In many cities, there are numerous active Wi-Fi networks on those preciously few non-overlapping channels—that's in addition to microwaves, bluetooth, cordless phones, and baby monitors, which all share the 2.4GHz band.

But since about 2007, Apple has also built support for 802.11n Wi-Fi on the 5GHz band into its computers and Airport line of Wi-Fi base stations. Now, the iPhone 5 and the latest iPod touch also have that support. (The iPad has had it since day one.) So, how do you set up a Wi-Fi network that makes the most of this confluence of Wi-Fi bands?

Not created equal

First of all, it's important to realize that the two bands are created very differently. The 2.4GHz band suffers from lack of non-overlapping channels and interference from other devices. But the lower frequencies pass through walls and floors reasonably well. The 5GHz band on the other hand, has a much larger number of channels—and they don't overlap—but the higher frequencies have reduced range, even in open air. In addition to this, Apple only supports using two channels as a single, double-speed wide channel in the 5GHz band. If all else is equal, 5GHz is twice as fast as 2.4GHz.

Older base stations, such as the first and second generations of Apple's Airport Extreme (released in 2007), support either 2.4GHz or 5GHz operation, but not both at the same time. If you have one of those, you have to choose. In a small apartment with thin walls, 5GHz has enough reach, and you'll benefit from the extra speed and reduced interference. Especially when you let the base station select the channel, because that way, more channels are available. But in a big house away from interfering neighbors, 2.4GHz gives you better coverage further away from the base station. You may also need 2.4GHz for compatibility with older devices that don't support 5GHz operation.

But fortunately, with newer Wi-Fi base stations, it's no longer necessary to make that choice: they support simultaneous dual band, operating in both the 2.4 and 5GHz bands at the same time. There are two ways to do this: having a separate 2.4 and 5GHz networks, or having one network that spans both bands. In the first case, you tell the base station you want a different name (aka SSID) for the 5GHz band. This means you can manually select the 2.4GHz network or the 5GHz network as needed. The downside is that if you join the 5GHz network, and then move away from the base station, you'll remain connected to the 5GHz network and get spotty performance at distances that 2.4GHz handles just fine.

For most people, the best choice is to set up a network that does both 2.4GHz and 5GHz as a single network. This is what Apple's Airport Utility sets up for you if you don't tell it to use a separate 5GHz name. The benefit to this is that a single dual band network allows wireless devices that support both bands to switch to the band that has the best signal dynamically.

The iPhone 5 supports 72Mbps at 2.4 GHz, but 150Mbps at 5GHz. Most of Apple's computers have two antennas, so they can do 144Mbps at 2.4GHz and 300Mbps at 5GHz. My iPhone 5 quickly jumps from 5GHz to 2.4GHz when I walk down the stairs, but when I return to the living room, it typically takes a few minutes for it to switch back to 5GHz. And sometimes devices or computers get stuck on the 2.4GHz band just when you want to transfer some big files.

Adding to the family

Things get more interesting if you have multiple base stations. If you give each of these their own settings, wireless devices will try to hang on as long as they can before switching to a different one, and when they switch, all ongoing communication gets interrupted. But it doesn't have to be that way. You can have your own multi-base-station Wi-Fi network with seamless roaming, just like a campus or enterprise network, but using regular base stations such as Apple's Airport Extremes or Airport Expresses. (I didn't test with non-Apple equipment, but it should work the same way.)

Seamless roaming between base stations happens when four things are the same between those base stations: the network name (SSID), the security settings, the DHCP server, and the router. This is easily accomplished by hooking up the second base station to a LAN port of the first base station and setting the second one up with the same network name and the same WPA2 password. Then, tell the second base station that it should operate in "bridge mode," rather than perform NAT or DHCP.

It's also possible to set up a second base station as a wireless network extender to get more reach without putting in additional Ethernet wiring, but that requires extra wireless hops for each packet, so it reduces speed. In the wireless extender configuration, the second base station needs to be on the same channel as the first one. But if the second base station has a wired connection, it should have its own channel for best performance.

Don't forget that you can install the Airport Utility for iOS on your iPhone, iPod touch, or iPad, which lets you reconfigure your Airport base stations as well as monitor signal strength, connection speed, and the use of 2.4 vs 5GHz for all of their wireless clients, including iOS devices. Don't select a base station too fast, though, because then the list of wireless clients may not be shown.

Bonus tip: if you want to see what other Wi-Fi networks are active in your area, use the following command on your Mac:

/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -s

I did some speed testing with an iPhone 5 and a fourth generation Airport Extreme base station. In normal Web browsing or e-mailing, there didn't seem to be a speed difference. On 2.4GHz, iTunes Wi-Fi sync topped out at 2.8 megabytes per second, while on 5GHz, this was about 50 percent faster at 4.3MB/s. However, I was able to transfer a file from the Air Sharing app using the Finder at no less than 10MB/s at 5GHz. The Speedtest app showed that the iPhone was able to saturate my 60Mbps Internet connection at 5GHz, but barely more than half that at 2.4GHz.

On the other hand, I find that when using a 5GHz-only network, dropping Wi-Fi connections and problems reestablishing a connection are much more common. In the dual band configuration, issues with 5GHz aren't an issue, because the wireless device simply falls back to 2.4GHz. Life is good with dual Wi-Fi bands.

Update: this story originally said 5GHz support was new in recent iPads, while in fact it was already present in the original iPad.