Friday, December 04, 2009

Wi-fi interference

I have often complained about the increasing amount of radio interference and its effect on amateur radio operation. But it is not just ham radio that is affected. Other wireless devices are too. The latest problem of this type that I encountered concerns a wi-fi internet radio called the MagicBox IMP Adapt.

My wife and I enjoy listening to classical music. One day some time ago I was trying out some internet radio tuner software and discovered several stations online that played non-stop classical music with few announcements. One that I particularly liked was WCPE, from North Carolina. I wanted to listen to it through the hi-fi system instead of the computer speakers so I bought an IMP Adapter, a dedicated "internet radio".

The IMP worked fine for a year or so but the other day it started freezing at "Initializing network" and then apparently rebooting. I wondered if it needed a firmware update but none was available. I did a bit of Googling about the problem and discovered several interesting things about it. Apparently this and most of the other wi-fi internet radio devices on the market are not specially designed custom electronics as you might expect, but general purpose computers with ARM processors running Linux! And a group of clever people called the Sharpfin Project had developed a system to enable you to bootstrap later versions of the software designed for other models of internet radio, even though they are no longer available from the original manufacturer.

This didn't help me much, because in order to bootstrap new software on to the device I needed it to connect to the network, and it wouldn't. But I discovered that the firmware wasn't the cause of the problem anyway. As you can see if you take the thing apart, the little embedded computer has a USB socket on it, and plugged into that is a bog standard USB wi-fi adapter. Apparently the one used with the IMP Adapt falls over in the presence of the latest IEE 802.11n wi-fi signals, which are becoming increasingly common being supported by the free wi-fi routers being given out by all the major broadband providers.

When I first moved here, only geeks had home networks. I never even bothered encrypting or securing my wireless network as the neighbours are mainly retired people or had no interest in computers and the likelihood of them trying to hack into my computers seemed negligible. Today if you open the "view all wireless networks" window on my laptop you have to scroll down to see them all. Obviously my wireless adapters are struggling to receive my network's signal among all the competing signals. In fact, I've just ordered a pair of 10dB gain wi-fi antennas for my router.

But back to the IMP Adapt. I found that there is a simple and fairly inexpensive solution to the rebooting problem, and that is to replace the existing USB wi-fi adapter with a different model. There is no guarantee that any old USB adapter will work with the drivers in the IMP's Linux kernel. But I discovered that the Edimax EW-7318UG adapter will work. It's also cheap - currently £7.99 from - so it was worth a try. I ordered one, it came this morning, I fitted it and now the IMP connects with no trouble and works as well as it did originally. I had an anxious moment as it didn't look as if it would fit in. But I found that you can remove the plastic cover leaving the bare circuit board and then it fits in perfectly.

Now that the radio had network connectivity I used the Sharpfin software to install a newer firmware that provides a few extra features. So now not only can I listen to WCPE The Classical Station on the hi-fi again, I can also control the radio using a web browser, and telnet into it and change configuration settings. I could even write programs using free software tools and run them on it. Not that I particularly want to, but it does show that the IMP Adapt really is a little Linux computer.

I expect a lot of these IMP adapters and others that use the same 802.11n-incompatible wi-fi adapter are thrown away because they don't work any more. If you come across one, it might be worth salvaging. I'm sure someone could think of other uses for a little Linux computer with a three line LCD display, a network interface and a stereo audio output.

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