Welcome to the World of Wi-Spy. This hands-on exercise reviews the fundamentals of spectrum analysis using MetaGeek's Wi-Spy DBx and Chanalyzer Pro software. Wi-Spy devices are designed to detect RF activity levels in the public ISM bands. These are the same RF bands that Wi-Fi and many other wireless consumer electronics use. By measuring the wireless energy created by all devices within the Wi-Fi bands, Wi-Spy can accurately measure where contention for frequency space occurs.
Run Chanalyzer Click on the start menu to access the “MetaGeek” directory. Select Chanalyzer Pro to launch software. Chanalyzer Pro MetaGeek developed the Chanalyzer software package to translate data captured by Wi-Spy hardware and Wi-Fi cards into easy-to-understand, actionable information.
Navigation Pane The Navigation pane provides controls for browsing Wi-Spy / Wi-Fi capture sessions or recordings. The following table describes each component of the Navigation pane. Device Selector With two Wi-Spy devices, you can alternate between the 2.4GHz band and 5GHz band without creating additional files. Chanalyzer Pro continuously logs data from multiple sources. To toggle between Wi-Spy spectrumm analyzers click the Sessions to the right of the waterfall view.
Waterfall Navigation Waterfall Navigation displays all data in the current Wi-Spy session with visual indicators to show the section of time detailed in the Overview and Details displays. To jump to a specific position within the session, double-click the point within the waterfall. User can then click-and-drag the head and tail of the highlighted region to easily adjust the timespan in the Waterfall Navigation. This functionality allows users to quickly drill-down to specific points in time.
Color by Density The more often a signal is detected at a specific amplitude and frequency, the brighter the point on the graph becomes. Low density signals are represented by dark blue, and high density signals are represented by red. Color by Amplitude Chanalyzer creates a density map of the most used points in the user-selected timespan. The less trafficked frequency points appear more transparent, while high-use frequencies appear more bright or intense.
Users can choose which tabs to display and which to hide by selecting "Tabs" from Chanalyzer's top menu. News The News tab keeps users up-to-date by displaying the latest Wi-Spy and MetaGeek news. Showcase The Showcase tab provides access to many example recordings and is a great place to start for users who have never before used Chanalyzer or Wi-Spy devices. Signatures The Signatures tab is where users can find all of the built-in Classifiers that Chanalyzer uses to identify RFtransmitting devices.
Networks Graph Click the Networks Graph to show signal strength over time. This data comes from the wireless network card. It draws the rows selected in the Networks Table. Drops in signal strength indicate poor signal coverage and can be referenced against the Waterfall and Density views to determine if interference is to blame. Networks Table The Networks Table is a list of Wi-Fi access points that are within range of the computer’s Wi-Fi card.
Channels Table The Channels Table “grades” each Wi-Fi channel, based on RF activity within the given frequency range during a selected timespan in the Navigation Waterfall. It considers all RF noise, Wi-Fi or non-WiFi, occurring within each Wi-Fi channel. A high grade represents a clear channel, while a lower grade indicates a noisier channel. The Utilization (Duty Cycle) is a relative score that helps determine how usable a specific channel is.
First Spectrum Analysis Experiment Now that you're familiar with the Chanalyzer Pro interface, let's go through a step-by-step example. To follow along with this user guide, you will need a Wi-Spy 2.4x or a Wi-Spy DBx. Plug in a Wi-Spy (Wi-Spy 2.4x or Wi-Spy DBx) Launch Chanalyzer Pro software Select Wireless Card Select the built-in wireless card in the top right corner to access additional WLAN information about SSIDs, RSSI, MAC address and data rate. *Wi-Spy is a spectrum analyzer.
Use a Two Minute Time Segment For this exercise we will be using a Timespan of two minutes. Adjust the Timespan in the Navigation pane by clicking the green or red arrows to two minutes. Wi-Spy capture playback options The Overview and Details panes will update to display data from the indicated timespan. MetaGeek calls this a Unified Time Segment. All graphs and tables display information for the exact same time segment.
Press the pause button in the Chanalyzer Timespan controls when the microwave oven is about to stop. Since the Timespan is set to two minutes, and we ran the microwave for two minutes, the time segment selected in the Waterfall View will show the microwave oven RF activity. You have paused the Chanalyzer capture in much the same way a DVR is paused. Chanalyzer continues to collect data from the Wi-Spy even while paused. Observe the data in the waterfall navigation pane.
Add a Density View Block to the Report At the top of the Report Builder interface, select add graph (the first button) and choose Density. Each of these menu items will add a graph block from Chanalyzer to your report . Update the Density Block If you are not satisfied with the captured image, you can easily refresh it. Move the Timespan and turn off the network overlay at the top. Then click the refresh button at the top of the block.
Edit the report block details to change the title. Give the block a title to relate it to the microwave oven like “Microwave Oven Interference.” The Channels Table is used to compare a Timespan when the microwave oven was not running. Point out the channels with an increased Utilization or lower grade. Navigating the Waterfall View Like a seismometer measures vibrations of the earth, the Waterfall View in Chanalyzer Pro does the same thing for your RF environment.
Add another Density View block and Channels Table By adding blocks from two different spans of time, Chanalyzer Pro can help users explain to customers and management the negative impacts of interference. During site surveys, a wireless professional may decide to add several blocks per location. They will often turn on all wireless devices in the area to create a worst-case scenario, which allows them to choose the most interference-free channel for their WLAN.
another .wsxr file. To do so, click “Append.” You might add a pre-built, vendor-specific block set discussing the latest features available and how they relate to the current spectrum data. You can also include product images or digital photos. Interference Identification by Signature Most modern spectrum analyzer solutions offer some form of device classification, though many are rudimentary.
802.11g ERP-OFDM Identify 802.11g ERP-OFDM by looking for a flat top. The flat top of OFDM signatures are under 20 MHz wide.This is the same signature for 802.11a OFDM. The second image is a more typical representation of what ERP-OFDM looks like in the 2.4 GHz band. 802.11n 2.4 GHz 40-MHz ERP-OFDM 802.11n OFDM 802.11n APs with data rates of 300mbps use channel bonding, which appear as two 802.11g ERP-OFDM signatures bonded together. Notice how the 40 MHz wide 802.
Non-Wi-Fi Patterns Microwave Ovens Microwave Ovens operate in the 2.4 GHz range. Use the Density View of Chanalyzer to identify microwave oven leakage. Typically they create a sloping mountain shape in the Density View. Since microwaves are usually used from 1-5 minutes, it helps to adjust the timespan to about two minutes. Interference occurs when the microwave oven transmits on the same frequencies as the Wi-Fi channel.
Motion Sensors Motion sensors tend to transmit in very narrow frequency ranges. Sometimes a building will have motion sensors in each room. If this is the case, verify that they are not in the 2.4 GHz range by walking close to each sensor and watching the corresponding amplitude levels in the Waterfall View. Audio Video Transmitter Wireless security cameras generally create three spikes. They constantly transmit and rarely change channels. Look for three vertical lines in the Waterfall View.
Bluetooth Bluetooth hops across the 2.4 GHz 1,600 times a second, which is a form of frequency-hopping spread spectrum (FHSS) modulation. Due to the nature of frequency-hopping transmitters, they may cause WLAN degradation, though it is unlikely that Bluetooth will cause severe Wi-Fi issues. Customize the Utilization Threshold Wireless engineers need to know how often noise levels cross a threshold.
Press Pause The Utilization graph shows a wide curved shape due to a lower Utilization threshold of -90dBm. Build a Signature Users can create Custom Classifier signatures in Chanalyzer Pro. To follow this example, please download the 16MB recording of a wireless audio projector made by Yamaha. http://files.metageek.net/recordings/yamaha.wsx Open the recording and select a five minute Timespan in the Navigation pane.
Use Playback Controls for Better Signature Results. Press Pause when the shape appears to match the Density View modulation pattern. You may also want to shorten or lengthen the Timespan to get data to better fit the shape. Narrowing-in on instances in the waterfall view offers the best results for pattern matching. Press Pause when you have found a good fit. Highlight the Shape to Create a new Classifier Signature Click-and-drag the mouse cursor across the shape of the transmitting device.
If a signature pops up for a few seconds then disappears and never comes on again, it is quite likely that this was a false positive. Tracking Down Transmitters Chanalyzer Pro’s waterfall view uses colors to map high amplitude points over time. This allows anyone with a spectrum analyzer to track down devices by watching amplitude changes over time. While walking around, the colors change to yellows and reds when a user is approaching the transmitting device.
Adjust the Timespan to select the range of time in which the amplitude was the highest (most red). Since the software continuously logs data from the Wi-Spy, we can zoom-in to view just the minute when the transmitter was within close range. A shorter timespan helps users identify what type of a device was transmitting. Once the Timespan is shortened, we see three spikes of activity above Wi-Fi Channels 8 and 9. Using the signatures tool, we can match the recorded pattern to an AV transmitter.
When performing site surveys, directional antennas minimize the guessing associated with determining where interferers are transmitting from. Instead of going into each room to see if amplitude increases or decreases, Wi-Spy users with a Device Finder directional antenna can rotate it to find higher amplitude levels and walk in the direction until the transmitter is located. Users can highlight frequency ranges of a transmitter’s peak signal and track it using a directional antenna.
