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USB dongle sweeps 2.4GHz ISM band

Posted: 19 Apr 2006 ?? ?Print Version ?Bookmark and Share

Keywords:Wi-Spy? RF spectrum analyzer? MetaGeek? Alex Mendelsohn?

Wi-Spy plug-in spectrum analyzer

Don't you just love this sort of product? MetaGeek's less-than-$100 Wi-Spy plug-in is just the ticket for rudimentary analysis of IEEE-802.11 b/g/n Wi-Fi networks. It works in conjunction with your PC.

Sure, it won't replace your $25,000 benchtop spectrum analyzer, but it can reveal a lot about what's going on in a wireless environment. It's sure to win the hearts and minds of installers and network administrators, but it might just find a place in the lab on the bench, too.

Spanning 2.4GHz to 2.483GHz, the diminutive Wi-Spy can give you a handle on pesky interference from other ISM (industrial, scientific and medical) network devices, as well as emitters such as microwave ovens, cordless phones, and Bluetooth devices.

Internally, the USB-based Wi-Spy module uses a Cypress Semiconductor CYWUSB6934 spread-spectrum RF and a Cypress CY7C63743 enCoRe low-speed USB controller chip. The CYWUSB6934 is a 2.4GHz direct sequence spread spectrum SoC in a 48-pin surface-mount package. This 3V device touts a sensitivity spec of -90dBm.

For its part, the CY7C63743 enCoRe (enhanced Component Reduction) works as the Wi-Spy's smarts. It's a low-speed USB controller, with an embedded RISC instruction set optimized for USB.

Just as the chip's RISC keeps the coding trim, the rest of the hardware follows suit. The enCoRe chip uses a non-crystal oscillator, for example, so no external quartz crystal or resonator is used, making the Wi-Spy ultra-compact. Other external components commonly found in low-speed USB applications, such as pull-up resistors, wake-up circuits, and voltage regulators are all on-chip as well.

Plug-and-play operation
To use the Wi-Spy, your PC will need to run Windows 2000 or Windows XP and Microsoft .NET Framework 1.1. However, other operating systems can also be accommodated; more on this in a moment. Your PC must support 1024 x 768-pixel resolution, or better.

Once the Wi-Spy is plugged into the PC's USB 1.1 or USB 2.0 port, analysis is shown on-screen in nifty graphical displays that resemble what you'd expect on a more expensive RF spectrum analyzer. Wi-Spy enumerates as a generic USB HID (Human Interface Device). No drivers are required.

The first time a Wi-Spy is plugged into your USB port, enumeration can take about twenty seconds, but subsequent enumerations usually only take a few seconds. When the device has been recognized, a green LED on the device lights and a Dongle Enumeration Indicator on the associated Wi-Spy software lights up. There's no other configuration or registration required.

Fast sweeping
With the software installed and the Wi-Spy plugged in and recognized, the system samples signal strength of every frequency in the ISM band, sweeping at 96ms. It then calculates the maximum signal strength, and the average signal strength for each frequency.

Wi-Spy can also selectively show data and/or average and/or maximum traces. What's more, its spectrogram view can display the amplitude of each frequency over time. That gives you a way to analyze two minutes of traffic on a band.

Network visualization
This is also useful when setting up a network and its access points. Indeed, the boundaries of Wi-Fi channels are hard to remember and visualize. As such, the Wi-Spy analyzer provides visualization. You mouse-click on a Wi-Fi channel number and the channel boundaries are then displayed on a graph. This gives you a visual indication of what channels are the quietest when setting up new access points.

The system's spectrogram view provides a time-based history of the ISM band. This historical view can span two minutes to 24hrs. The spectrogram is also color-coded to show amplitude, with low levels shown in shades of blue, and with medium amplitudes in shades of green, yellow, or orange. High amplitudes are displayed in shades of red. Black-and-white images can also be displayed.

By default, three traces (data, average and maximum) are displayed. You can enable or disable a frequency marker or any of the traces from the Windows toolbar, a View menu or using keyboard shortcuts.

If a marker is enabled, the frequency and amplitude of a current marker position is displayed, and the marker can be moved left or right by dragging it with the mouse or keyboard.

Your views can also be changed from a Frequency View to a Channel View/In Frequency View the horizontal axis of the display is labeled with frequency in MHz.

In Channel View the axis is labeled with Wi-Fi channel numbers. When your mouse is held over a channel number, the frequency range for that channel is highlighted. Clicking the channel number permanently highlights the frequency range for that channel.

Record and playback
The Wi-Spy can also record data to a file and then play the file back. Recordings can be re-played in a separate tab for comparison with real-time data, as well as with other recordings. Your network recordings can also be played in fast-forward mode.

Note that the Wi-Spy is fully functional while playing a recording. As such, traces can be turned on and off, and history can be cleared. This gives you an in-depth analysis of problems, as well as the ability to e-mail stored traces.

Wi-Spy also supports printing. Wi-Spy can also save images in a variety of popular formats such as .BMP, .GIF, .JPG, .PNG and .TIF. These image files can also be copied into other popular Windows applications, such as documentation in Word or into PhotoShop.

Other platforms
Not interested in Windows? Well, don't fret. Mike Kershaw, the author of Kismet, has an open-source version of Wi-Spy software.

It runs on Linux, BSD and Mac OS X operating systems. Kershaw's code is also under development and is progressing to become a feature-equivalent to the Windows Wi-Spy version.

- Alex Mendelsohn

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