Troubleshooting Tips – AirSleuth Spectrum Analyzer

Question: Which products support an external antenna? Answer: The PC Cards that come with the PCMCIA versions of AirSleuth-Pro have an MMCX connector that can be used with an external antenna.  We recommend replacing the snap-on antenna with the external, omni-directional antenna provided in the package.  We have found that both laptop and desktop machines may generate RF signals in the 2.4 GHz range and if the antenna is too close to the machine (e.g. the PC Card's snap-on antenna) then it becomes more difficult to interpret the frequency data (since you'll need to take into account that the source of some signals may be the machine's internal components).  By locating the external antenna several inches from the machine you'll achieve more accurate results.

Question: During the software installation process the Setup wizard complains about not being able to create files or access the Registry. Answer: If this occurs it probably indicates you’ll need to repeat the installation from an account that has Administrative privileges.

Question: Does AirSleuth interfere with my existing wireless network? Answer: No.  When the AirSleuth application is running the wireless device that it communicates with is operating in a “passive” mode – hence, it will not interfere with your existing wireless network.

Question: When using an external antenna, does it's location or orientation make a difference? Answer: Whether using the PCMCIA or USB wireless device, the orientation of the antenna may influence the strength of RF signals measured by the device. From the ‘Traces’ view, experiment by changing the orientation of the antenna to see what affect that has on the frequency spectrum displayed by the application.

Question: How can I verify that the analyzer is working? Answer: As a quick check you could turn on a microwave oven. This will generate radio waves across the entire 2.4 GHz spectrum. An even better test would be a 2.4 GHz cordless phone – most seem to transmit a continuous signal in the vicinity of 2.41 GHz (i.e. approximately in the middle of 802.11 channel 1).

Question: What is the relation between frequency and 802.11 or WiFi channels? Answer: The 802.11 wireless protocol divides the 2.4 GHz frequency spectrum into 14 channels.  Moreover, there is a lot of overlap between channels – that is, a particular frequency will belong to more than one channel.  An access point (AP) is configured to use one of the WiFi channels. When an AP communicates with its client stations it uses a range of frequencies within the channel – not just the ones in the middle of the channel.

Question: At my office (or home) I have an AP configured to use channel 6. I expect to see a big peak of activity around channel 6 on the analyzer – but I don’t. Why is that? Answer: 802.11 is a robust, wireless communications protocol that was designed to accommodate multiple 802.11 devices within close proximity. You could install multiple APs within a building and they would all work fine (for the most part) — even if they were configured to use the same channel. That is, 802.11 devices and networks know how to play nicely in a crowded backyard. (NOTE: problems do arise, though, when large files are transferred or someone streams video images). For a spectrum analyzer to detect a wireless device, that device has to (a) transmit continuously, and (b) the transmitted signal has to be strong enough and within range of the receiving antenna. 802.11 APs satisfy criteria (b), but unless the network is actively transmitting data between devices then the only transmissions are occasional beacon signals from the access point. The beacon signals alone are not sufficient for the analyzer to pick up — they are short in duration and occur approximately once every 100 milliseconds. As a result of their "bursty", intermittent pattern of beacon transmission then 802.11 access points don't generate a lot of signal activity that could interfere with other types of wireless devices that operate in the 2.4 GHz band. When a 2.4 GHz spectrum analyzer is combined with an 802.11 discovery utility — such as NetStumbler or NetSurveyor — the two complement one another to provide a powerful diagnostic tool for setting up and trouble-shooting WiFi networks. Keep in mind, however, the 802.11 discovery tool picks-up the intermittent beacon broadcasts from an AP and reports the signal strength of that broadcast transmission. This does not necessarily mean you will get good 802.11 performance when connecting with that AP — since after connecting to the AP there could be interference from other devices in the vicinity or there could already be many clients already associated with that AP.

Question: What kinds of devices could interfere with a WiFi(i.e. 802.11) network? Answer: When setting up a wireless network or trouble-shooting a poorly performing one –usually its the non-802.11 devices that you have to worry about most.  Things like wireless video or security cameras, bluetooth devices, cordless phones, wireless (baby) monitors, security systems, RF Excited lighting (Fusion lighting), wireless broadband (i.e. WiMAX), etc. Also, large file transfers and video streaming between 802.11 devices could degrade the performance of other wireless networks in the vicinity.

Question: In general, what kinds of things affect how a signal from a wireless device is displayed by the analyzer? Answer: Using a 2.4 GHz cordless phone as an example, 3 important parameters that will affect how a device appears to the analyzer include the following — the strength of the phone’s transmitted signal, the phone’s distance from the analyzer’s receiving antenna, and the orientation of the analyzer’s antenna relative to the radio waves transmitted by the phone. Changing the orientation of the analyzer’s antenna by rotating the device could change the results that are displayed. Another subtle effect, which is difficult to quantify but which you should keep in mind, is that when you move the transmitting device to different locations this will change the way the RF waves bounce off of objects and walls — which could affect the power of the waves on the receiving antenna and how the signal will be displayed.

Question: How do I install the external antenna that came with the PCMCIA version of the product? Answer: The PCMCIA card comes with a snap-on antenna. To remove it grab the card with one hand and the flat antenna between your thumb and index finger of your other hand. And then gently pull them apart. As you pull them apart you can jiggle (or rock) the antenna a little bit from side to side, but keep the card and antenna within the same 2-dimensional plane (i.e. don't twist). Once you remove the snap-on antenna it will reveal the card's female MMCX connector — which is where you'll connect the external antenna.

Question: When using AirSleuth-Pro to determine the ˜Best" channel to use for my access point (AP) what preliminary precautions should be taken? Answer: While the measurement is being performed temporarily power-off your known access point(s) – otherwise, legitimate network activity occurring over that channel will be interpreted as interference and could hurt that channel’s chances of being selected as the ‘Best’ channel.