Apple’s decision to use both the 2.4GHz and 5GHz bandwidth for their new 802.11n-ready AirPort Extreme wireless router could have negative implications for UK users.

Unlike many pre-n base stations already on the market, Apple’s takes advantage of a currently optional 802.11n feature, the ability to use either the 2.4GHz or 5GHz wireless spectrums. Most manufacturers, including Belkin, are only currently using 2.4GHz – the same frequency as 802.11g.

Dual band support means that the AirPort Extreme can operate in both 2.4GHz and 5GHz frequencies – which means Apple’s unit is able to support the full 802.11 spectrum: B, G and N, and A. Having the ability to operate in the 5GHz frequency is crucial as this frequency is less prone to interferences, according to Apple. It also means that if your 802.11n network has trouble with one spectrum, you can switch to the other.

However, it appears that this decision will limit the speed that can be achieved by the device in the UK, Japan, Austria, Estonia, Germany, Latvia, Slovakia, and Spain.

The company claims that the new Airport Extreme offers better data throughput than its immediate predecessor. In the US the new AirPort Extreme is up to five times faster than its predecessor. However, in the UK (and the other countries listed above) the device is just 2.5 times faster. The reason for the lag is UK government regulatory restrictions that prohibit wide-channel operation. The wide-channel operation that is restricted is the 40MHz channel that is found in the 5GHz frequency.

An industry source explained the implications of this to Macworld: “The 802.11n standard offers a bandwidth frequency that determines how much speed you will be able to achieve. This is either 20MHz or 40MHz, with 20MHz being 2.5x faster than 11g and 40MHz being 5x faster than 11g. I suspect that in the UK Apple's device is only able to use 20MHz because it is illegal to use the 40MHz bandwidth when using the frequency of 5GHz.”

If the source's theory is right it would appear that Apple is only able to promise speeds increases of 2.5 times is because of its choice to adopt the 5GHz frequency. “Most venders haven't adopted this frequency so they can use 40MHz and hence get the full 5x 11g speed,” explained Macworld’s source.

However, another industry source has suggested that it may not be possible to use the 40MHz band in the 2.4 GHz frequency. Interference from Microwaves, cordless phones and Bluetooth devices could lead to loss of performance, and neighbouring 802.11g devices would pull the 802.11n device back to 20 MHz, the source said.