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Bare-Bones Spectrum Analyzer Shows Signals Across the 2.4 GHz ISM Band

The manufacturer says . . .

ChipCenter's Alex Mendelsohn says . . .

Low-Cost Spectrum Analyzer Monitors Environments for RF Signals, Giving Confidence to Developers and OEMs Lenexa, Kansas--AeroComm's new SA3000 Spectrum Analyzer is a compact, cost-effective, PC-based instrument covering the entire 2.4 GHz ISM band. The device identifies optimal locations for wireless equipment and alerts installers to potential interference. When combined with a laptop computer, the SA3000 enables comprehensive remote site surveillance at virtually any location. The SA3000's sensitive receiver hardware interfaces to a desktop or laptop PC via a standard RS-232 serial port. Its small size and multiple power-supply options make it easily portable and ideal for mobile site surveys as well as for fixed-site use. Using an intuitive application-software package, the SA3000 closely simulates the display of a dedicated—and much more expensive—spectrum analysis instrument. Its operation is menu-driven, and on-screen displays are easy to read and understand. Any user from RF novice to expert will have confidence that all possible band interferers are found. The SA3000's software includes a number of tools for gathering and evaluating data, providing optimal performance at a fraction of the cost of bulky handheld devices with small LCD screens. The SA3000 displays can be configured to three user selectable parameters: frequency (sets center frequency of the display), span (sets the width of the display in MHz), and amplitude (indicates the strength of the captured signal). Several F-key functions then provide one-touch access to absolute and relative measurements of the captured signals. The process is straightforward. Before installation or activation of 2.4 GHz radios, the SA3000 can be used to observe any competing signals. If interference is found, the SA3000 will help to identify the sources and evaluate their strength. Once there is a good understanding of the environment, the user can choose good positions for the radios. Here, a server radio would be turned on to emit a beacon while the SA3000 is walked around to identify where the beacon can be heard. Its signal strength would show suitable spots for repeaters and client radios. As a specialist in the field of 2.4 GHz transceivers, AeroComm is committed to providing simple, affordable tools to enable wireless installations with minimum fuss—the company's concept of "Instant Wireless." As part of this strategy, the SA3000 will be a valuable aid to engineers and developers involved with the integration of RF. The system is now available through AeroComm, Avnet, and other major distributors worldwide for $1499.

The SA3000's tiny size and featherweight 6 oz. bulk may initially give you the impression that there's not much to this instrument, but that assumption would be a mistake. With its 4.4" × 2.7" footprint and Z-height of barely 1.5", keeping this little receiver pinned down on your bench may be its biggest drawback. In use, the SA3000's hardware is controlled by a simple MS-DOS application package that supports serial communication with the box across a 9-pin connection running at 115.2 kbits/s. Once that connection is established (and confirmed by LED indicators), the analytical capability of the SA3000 package comes into play. Aerocomm notes that although the SA3000 software runs under MS-DOS, it needs to do that via a Windows 95, Windows 98, or Windows Me window. The company says that Windows NT and XP systems will also run the application, but cautions that the supplied executables will run slowly unless you prepare a DOS boot disk and boot the PC to DOS. Yuk. Around the ISM Band In any case, once up and running, the DOS software lets you look at activity in the ISM band. Although the press release indicates that the system covers 2.4 GHz to 2.483 GHz, the box actually permits you to monitor local RF signals in and around the band. The SA3000 can show both in-band and out-of-band signals, as its range spans a low of 2.38 GHz to a high of 2.51 GHz. Picking up signals with its built-in rubber ducky-style antenna, the SA3000 lets you set the center frequency of interest. You can also set a frequency span that can be between about 7.29 MHz to 175.04 MHz, and set markers. The SA3000's sweep time is configured dynamically to match the span. Coarse But Meaningful Remember, this is not an expensive lab-style CRT-type spectrum analyzer. The software display shows the band's activity in a somewhat coarse histogram-style display. Nonetheless, you see levels in dBm with ± 100 kHz accuracy. The system's input-amplitude range extends from -20 dBm to -90 dBm, but it will safely accept overloads to +23 dBm. The amplitude accuracy is within ± 2 dBm. Freezing Signals Using the software, you can also establish a reference amplitude, and use that along with Max Hold and Marker Peak Search functions actuated by a PC's Function keys. The Max Hold feature is neat, as it can capture and freeze random occurrences of signals. The typical display shown here shows the magnitude of energy radiated from a microwave oven located at a distance of about eight feet from the SA3000's antenna. In this example, the unstable broadband microwave energy sweeps across the band, so to get a picture like this you would engage the SA3000's Max Hold function with a Function key for about 30 seconds. click for full-size image The amplitude setting on the display is at -20 dBm, and the system's Peak function shows that the highest level of RF from the oven is almost -31 dBm. You may also observe signals from devices such as nearby Amateur Radio emitters or cordless phones. Thanks to its small size and portability, you can potentially use the SA3000 to track these signals to their source using a laptop to run the software. On the bench, the SA3000 derives its operating power from a 120 V wall wart, but when taken afield it can steal DC power from a laptop's Universal Serial Bus (USB) or PS/2 port. It will accept sources between 5 V and 7 V, and typically pulls about 115 mA. Although the SA3000 isn't a full-blown spectrum analyzer with all the bells and whistles that those types of instruments convey, it should serve as a useful RF sniffer during development and/or deployment of ISM-band systems, especially if you don't mind the software-generated display. Considering its reasonable price, you may even want to run more than one SA3000 when doing a site evaluation.

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