Understanding Wi-Fi's two spectrum bands

The evolution of communications is about taking one kind of thing and making it better, faster, and more reliable. USB 1 evolved into USB 2; FireWire 400 morphed into FireWire 800; 10 Mbps Ethernet moved into 100 Mbps and then 1,000 Mbps. Where there's a choice, it's between a worse, older alternative and the latest and greatest.

Not so with Wi-Fi, which has an interesting current tradeoff with Apple's implementation in hardware and software. You're given a significant choice as to which spectrum band to use or whether to let Mac OS X decide for you. The choice you make has a huge impact on the distance, robustness, and speed you can eke out of a network without wires.

Wi-Fi can work over one of two spectrum bands: 2.4GHz or 5GHz. The two bands have quite different properties, and in the past Apple's AirPort Base Stations have only been able to use one band at a time. But the AirPort Base Station and Time Capsules released in March 2009 can operate simultaneously over both bands, removing some of the difficulty of building Wi-Fi networks that work best for whatever devices we attach to them.

Apple also supports both bands in Macs and the Apple TV as network clients. Nearly all Macs with Intel processors work in both bands, while nearly all Core 2 Duo Macs (and Mac Pros with Wi-Fi) also handle the latest 802.11n Wi-Fi spec. (First-generation Intel Macs have dual-band support, but only for an older standard in 5GHz.)

With all this dual-band support, Apple has tried to keep you from having to make a decision about which band to use, automatically choosing the right frequencies for speed, consistency, and range based on where your computer is relative to a base station at any given time.

Often, taking Apple's suggestions makes the most sense, but other times, you want to override automatic selection and other options to produce better, more consistent throughput and range. I'll look at common problems and solutions that might plague you in the 2.4GHz and 5GHz bands, and then offer advice for manually setting channels in both bands or creating two unique networks with a simultaneous dual-band base station.

Band tradeoffs
Wireless networks work by having a wireless base station transmit data on a given range of frequencies to another device. Both of the frequency bands used by Apple's base stations are unlicensed, which means any individual or organization can build a device that sends signals in the frequency range covered by the band without obtaining permission.

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