After Hours

Does your shop need a spectrum analyzer?


To help explain why spectrum analyzers are needed, it would be best to first define Radio Frequency Interference (RFI). RFI is produced by a RF generating source on the same frequency or nearby frequencies (when considering 802.11 spread spectrum technology) that erodes the quality of another RF communications link. For example, two 802.11 wireless networks that share the same channel and coverage area would consider each other RFI. Some inadvertent examples of RFI could be a defective fluorescent light fixture that is emitting RFI and happens to be located right next to an 802.11 access point. Another example would be RFI emitted from a poorly sealed microwave oven which affects the same 802.11 access point, but only randomly. The examples are numerous and whether the source is emitting RF by design or not, it's still RFI to the wireless device that is being interfered with.It quickly becomes apparent that RFI should be one of many considerations during site surveys, network setup, and whenever the wireless network is not operating normally. By doing so, the administrator then has a complete understanding of the RF environment, which allows for knowledgeable decisions and solutions.

How is RFI located and measured? By using a spectrum analyzer, it's the only tool that gives the administrator a clear idea as to what's happening on the RF band being tested. Spectrum analyzers are also helpful in determining if, how many, and what other channels are being utilized by foreign wireless networks.

So if it has the potential to be such a useful tool, why doesn't everyone have one already? It's not that much of a puzzler--most spectrum analyzers are very expensive and purchasing one is hard to justify with tight IT budgets. Fortunately about two years ago a company called MetaGeek.net developed the Wi-Spy spectrum analyzer with a price tag that was thousands of dollars less than other analyzers. To maintain the low price, many of the features seen in the high-end analyzers are not included. But Wi-Spy is still capable enough to alert wireless network administrators of any RFI conditions.

MetaGeek.net has recently released a new spectrum analyzer called Wi-Spy2.4x. Tim Higgins published an excellent review of the new Wi-Spy2.4x, pointing out all of the improvements. The review also compares the Wi-Spy2.4x to the original Wi-Spy and the Cognio Spectrum Expert which is considered a high end spectrum analyzer. As stated in the review either of the Wi-Spy devices would be a welcome addition to the tool kit of an 802.11b/g wireless network administrator.

Like most networking tools, the Wi-Spy device has a learning curve. To help with this the MetaGeek.net website includes support for the application software. Especially useful is the web page containing actual recordings of known RF generators.

About

Information is my field...Writing is my passion...Coupling the two is my mission.

5 comments
TheChas
TheChas

There are lots of other ways than using a spectrum analyzer to locate RFI and other transmission sources. Any AM radio tuned to an open channel will receive just about all the RF noise in the area. A decent battery powered radio with shortwave bands can be used to identify a specific noise source. For many people, the easy way to deal with RFI problems is to find and work with a local Ham Radio club. These guys live to use their radio tracking skills. Don't get me wrong, a spectrum analyzer can be a great and useful tool. It is a great tool for finding what types of RF noise are in your area. But, for most situations, they are neither cost effective or practical. Chas

mjd420nova
mjd420nova

Not enough band width. Prefer to rent the range we need or plugins for the unit we have. A real specification to look for is how many stage conversion and resolution MAX. I also recommend renting a good dish or LNA. Unless you have a phased array a dipole won't help much.

jdavis
jdavis

One big drawback that jumped out at me is no 802.11A (5 GHz) support. -JD

Michael Kassner
Michael Kassner

I agree with your suggestions whole-heartedly. Being an amateur radio op, I do agree with your comment about that aspect. I find that I like using a spectrum analyzer to visualize channel usage as well as RFI, but as you suggest it is not essential. It is just an ancillary feature since I already have an analyzer. In finishing, I just thought it would be a relatively simple and cheap tool for use by network admins or field engineers such as myself that are having difficulty resolving RF problems.

Michael Kassner
Michael Kassner

It is my understanding that MetaGeek is developing an 802.11a device. No information as to when though.

Editor's Picks