- ✓Very capable and convenient PC Card hardware
- ✓detects, plots and analyses signals in the 2.4GHz and 5GHz frequency bands
- ✕Software requires a usability makeover
- ✕no logging, automatic data capture or remote control functionality
Invisible problems are the hardest to fix, and until we evolve eyes that respond to radio waves, wireless will remain thoroughly out of sight. Radio engineers have long bypassed their organic shortcomings with specialised test equipment, the most highly prized of which is the spectrum analyzer. This sweeps through a band, plotting energy received at the frequencies where it’s found. With practice, all manner of problems can be recognised by the patterns they make.
AirMagnet’s Spectrum Analyzer is a combination of software and hardware that provides a notebook not just with the ability to detect signals and plot them, but also delivers an expert system that recognises and diagnoses common interference sources on the Wi-Fi 2.4GHz and 5GHz bands.
The hardware is a full-size PC Card with two lights for power and frequency sweep, and an antenna socket. The card has an internal antenna, and also comes with a stubby external whip that clips onto the top of the notebook's screen and connects via a short length of thin co-ax. You cannot easily remove this once plugged in, and the software warns that damage can be done if you try.
This PC Card does most of the work, and can simultaneously sweep the 2.4GHz and 5GHz bands while performing analysis of the signals it detects. This keeps the load off the notebook, which is left with the duties of displaying the results and controlling the card.
Unfortunately, the usability of this software is uneven. Although you can have as many windows on-screen as you like, reflecting different views onto the data the card is collecting (including waterfall and live FFT spectrum analysis), you can’t change their position or resize them. Furthermore, each view starts in a dormant mode, so you have to enable each trace separately. There’s no way of saving logs of events or of spectral scans, short of taking a screenshot, and no way of automating data capture or running the system remotely down a narrow bandwidth connection. These are all things that can be exceedingly useful if you’re trying to diagnose an intermittent or time-based problem in an inconvenient place.
There are plenty of other frustrating usability issues, such as no error trapping on frequency data entry. This is software that’s been written by engineers to a very basic specification, and it badly needs to be updated. Since the hardware seems so capable, this is particularly disappointing.
On to the good stuff. The card seemed very sensitive; in a block of flats, it detected at least five different microwave ovens, and could pick up access points at least thirty metres beyond the range at which the notebook itself could make contact.
The automatic interference analyser wasn’t initially very quick to spot microwave oven interference, due to the different mains frequencies in the US and here. Microwave ovens are monstrous devices broadcasting chunks of raw power modulated by the mains frequency, and it's this that the automatic detector checks. A revision of the software received during the course of the review fixed this -- and in any case, the pattern a microwave oven makes on the display is as easy to recognise as someone spray-painting a smiley on the Mona Lisa.
Other interference sources were much easier for the system to recognise. Bluetooth, spread-spectrum cordless phones (not sold in Europe, but often imported by individuals) and continuous carrier systems like video were all reported and analysed within seconds of being detected. Wi-Fi signals themselves were easy to spot by eye, and the startling amount of congestion visible in a central city office caused by bleedover from nearby hotspots and other companies eloquently explained some throughput problems. It also showed how empty the 5GHz band is (a strong argument for using 802.11a if your local licensing conditions permit), with only one interfering source (apparently military in nature, which probably renders us liable to prosecution) detected during the test.
For the specific purpose of diagnosing Wi-Fi interference problems, the AirMagnet Spectrum Analyzer is a good product. But it could be so much better -- and at the price, it's a shame that the company has not created better software. It says that logging and remote control are both being actively investigated and will be provided at a later date: an alternative would be to publish the interface to the card so that the creative might of the open source community could get to work.