Wireless Reviews

Introduction

6/27/2007 - Updated Table 2 with WiSpy resolution bandwidth

At a Glance
Product	MetaGeek Wi-Spy 2.4x Spectrum Analyzer
Summary	Second generation of (relatively) inexpensive 2.4 GHz USB spectrum analyzer with improved resolution and range
Pros	· Inexpensive compared to alternatives · Improved frequency resolution · Improved amplitude resolution and range · Record and playback capability
Cons	· Can't control sweep rate · Can't manually set view amplitude · Price will put off some buyers

It's been almost a year and a half since MetaGeek's original Wi-Spy 2.4 GHz spectrum analyzer hit the street. I thought it was one of the coolest and most useful products I'd seen in a long time, especially for the $99 price. And I urged anyone who had been needing or thinking about 2.4 GHz spectrum analysis to buy one.

Since that review, MetaGeek doubled the price to $199, which caused much tooth-gnashing and garment-rending among its fan base. But the increase corrected a price that was probably way too low to begin with to support a viable business and further development.

Well, it looks like the Geeks put the extra money to good use to develop the Wi-Spy 2.4x, with better performance and the ability to use higher-gain antennas. But they also have once again done the price-doubling trick and set the 2.4x' price at $399. So let's see if it's worth it, shall we?

What it is

The 2.4x maintains its USB flash-key size, but now sports an RP-SMA antenna connector onto which you screw the small, swiveling 2 dBi dipole that comes with the module. The original Wi-Spy was a JUNO-USB dongle, manufactured by Unigen, that used a Cypress Semi radio and USB microcontroller.

Figure 1: Wi-Spy 2.4x board

The 2.4x' board shown in Figure 1 is a home-grown design using a Chipcon CC2500 2.4 GHz tranceiver and Silicon Labs C8051F326 (PDF link) USB microcontroller with 16K of flash built in. The design is so integrated that there are components on only one side of the board and nary a switch or even an LED in sight.

A summary of the key differences between the original and 2.4x are shown in Table 1 below, which I copied from the MetaGeek website.

	Wi-Spy	Wi-Spy 2.4x
Antenna	Internal	RP-SMA
Bandwidth	2.4 - 2.482 GHz	2.4 - 2.4835 GHz
Frequency Resolution	1 MHz	328 KHz
Amplitude Range	-97 dBm to -50.5 dBm	-110 dBm to -6.5 dBm
Amplitude Resolution	1.5 dBm	0.5 dBm
Sweep Time	~120 msec	~165 msec
Supported Operating Systems	Windows, Mac OS X, Linux	Windows, Linux, Mac OS X BETA

Table 1: Wi-Spy vs Wi-Spy 2.4x

While there are significant improvements in frequency resolution (3X), amplitude range (> 2X) and amplitude resolution (3X), I found the most noticeable and useful improvement to be the frequency resolution. The next most useful is the extension of the lower end of the amplitude range, which helps to sniff out low-level signals. There is significant range extension on the high-signal side, too. But since through-the-air signals rarely top -40 dBm or so, the high-side extra range isn't very useful.

Table 2 has been updated from the original review and compares the original and 2.4x Wi-Spies against the AirMagnet Spectrum Analyzer, which is essentially a rebranded Cognio Spectrum Expert.

	Cognio Spectrum Expert	Wi-Spy	Wi-Spy 2.4x
Frequency Coverage	2.4 GHz (802.11b/g) 5 GHz (802.11a)	2.4 GHz (802.11b/g)	2.4 GHz (802.11b/g)
Minimum Signal Level	-110 dBm	-97 dBm	-110 dBm
Frequency Resolution	10 kHz	1 MHz	328 kHz
Minimum Resolution Bandwidth	156 kHz	320 kHz	337.5 kHz
Views & Charts	Views - Real Time FFT - FFT Duty Cycle - Spectrogram - Power vs. Freq - Power vs. Time Charts - Active Devices - Devices vs. Channel - Devices vs. Time - Duty Cycle vs. Channel - Duty Cycle vs. Time	Views - Planar (spectrum) - Spectral - Topgraphic Charts [None]	Views - Planar (spectrum) - Spectral - Topgraphic Charts [None]
Plot Traces	- Max - Max Hold - Average	- Max - Max Hold - Average	- Max - Max Hold - Average
Movable Marker	Yes	Yes	Yes
Multiple Simultaneous Views	Yes	Yes	Yes
Record / Playback	Yes	Yes	Yes
Device List [1]	Yes	No	No
Auto Interferer ID [2]	Yes	No	No
Device Finder [3]	Yes	No	No
Saved Data File Format	Proprietary	Proprietary, but documented	Proprietary, but documented

Table 2: Cognio vs. Wi-Spy vs. Wi-Spy 2.4x Specs and Features

[1] Device List is essentially that same analysis capability put to use, but for identifying and displaying valid Wi-Fi devices.

[2] Auto Interferer ID represents the ability to analyze the signals being captured, match them against signatures of interferences sources such as cordless phones, microwave ovens and other RF sources, and display an indication of devices found.

[3] Device Finder allows you to choose an identified valid device or interferer and physically track it down by displaying a signal strength vs. time chart and real-time signal strength meter to be monitored as you wander around in search of your quarry.