No one wants to be told to check his cell phone, PDA or walkie-talkie at the hospital door, yet the potential for radio frequency conflicts and electromagnetic interference continues to grow as wireless devices proliferate — in and out of the hospital. For biomeds, the best defense is a good offense: a spectrum analyzer that can evaluate an area, collect test data and serve as a maintenance tool.

Just about everyone in the biomed biz recalls the now famous “Baylor incident” of 1998. The telemetry system in the Dallas, Texas, medical center’s cardiac care unit mysteriously malfunctioned. The culprit? HDTV (high-definition television). A local television station had just initiated a HDTV transmission, which interfered with the telemetry system. After a few harried hours, biomedical equipment technicians (BMETs) identified the source of the interference — thanks to a combination of BMET ingenuity and the help of a spectrum analyzer.

 Agilent Technologies’ E4440A PSA Series spectrum analyzer; SA1501 portable spectrum analyzer from Sencore.

For those unfamiliar with these devices, a spectrum analyzer is essentially a radio receiver with a display. These handy gadgets evaluate electromagnetic interference (EMI), a familiar issue when it comes to medical telemetry. Spectrum analyzers visualize and measure radio frequency (RF) radio carriers and spectral noise and interference carriers.

Today the potential for RF conflicts and EMI is growing because of the increased use of wireless devices by physicians, nurses and visitors. Glen Kropuenske, application engineer for Sencore Inc. (Sioux Falls, S.D.), states the problem. “Although wireless devices have existed for some time, the trend today in PC and medical equipment is toward more and more wireless devices. This will surely lead to more RF spectrum conflicts where signals are interfered with and service is interrupted.” A spectrum analyzer can identify interference — sometimes before it presents an obvious problem.

 Aeroflex’s 2399A portable analyzer; WCA 280A Wireless communication Analyzer from tektronix.

A spectrum analyzer can also serve as a maintenance tool. The user — the biomed — can check the signal on a medical device to make sure the signal is reaching its desired destination and not being transmitted where it shouldn’t be. Biomeds may also require the assistance of a spectrum analyzer during the installation of a new wireless system in the hospital. The spectrum analyzer checks for interference and verifies the signal of the newly installed equipment. A final application of spectrum analyzers in the healthcare arena is precompliance testing. This is generally the domain of equipment vendors who use the spectrum analyzer to sweep electronic devices prior to submitting for them for electromagnetic compatibility (EMC) testing. EMC testing is an expensive process; a spectrum analyzer can be used to identify problems prior to sending them for expensive third-party testing.

Despite the fairly widespread applications of spectrum analyzers in the healthcare business, some biomed departments may not have a spectrum analyzer on hand. However, the increasing complexity in the RF environment and the virtual explosion of wireless systems in the hospital may necessitate an investment in a spectrum analyzer. These gadgets do have a fairly long life span: The famed Baylor spectrum analyzer is still in use and is expected to last at least several more years.

Biomeds may encounter a stumbling block as they peruse the spectrum analyzer market: Most vendors do not target the healthcare market. But biomeds’ needs may not differ all that dramatically from those of other users. Two key factors to consider in selecting a spectrum analyzer are portability and ease-of-use.

Spectrum analyzers have come a long way since the days when they were the size of large appliances.

“Thirty years ago spectrum analyzers were very large products that required a two-person lift,” explains Bryan Harber, spectrum analyzer product manager for spectrum analyzers for Aeroflex (Wichita, Kan.). Now we’re getting into the realm of battery-powered spectrum analyzers that can almost be called hand-held.” The incredible shrinking spectrum analyzer is good news for biomeds. Says Kropuenske: “Portability is a must-have for biomeds. When you’re looking for interference sources you can’t be attached to the wall outlet.”

Sencore touts its new portable spectrum analyzer, Model SA 1501. The new device weighs in at 9.5 pounds and provides wide frequency coverage from 100 kHz to 1 GHz, which the company says should be sufficient to identify interference signals to medical telemetry systems. A block converter accessory extends the range to 2 GHz. Kelley Garland, clinical engineer with Baylor Health Care System, says hospitals need to track signals at lower frequencies from 400 to 500 kHz, but some may also need to try track frequencies at higher ranges, from 1.9 to 2.4 GHz.

Aeroflex’s answers to the portability issue include the IFR 2397 and 2399A spectrum analyzers. Both products weigh in at approximately 20 pounds and offer a frequency range from 9 kHz to 3 GHz. This range, and its relatively low price tag, may be sufficient for some biomeds. Harber says, “The frequency range depends on the products and technology you are looking at.” Many medical devices operate in the low-frequency range, but some are high-powered, microwave transmitting devices in the 9 or 10 GHz range. Even in those cases, the hospital may not need to shell out for a more expensive, high-frequency spectrum analyzer. That’s because the spectrum analysis tasks may fall under the service contract with the device vendor. The other issue to consider with frequency range is interference from the countless wireless devices used by physicians, nurses and visitors. Right now, all wireless LANs (local area networks) must be less than 2.4 GHz, which falls within the 9 kHz to 3 GHz range.

Once you get beyond the frequency range of a spectrum analyzer, there are other specifications to consider. The IFR 2397 features a marker system that can display nine markers on the screen at one time with a marker table showing the frequency and level of each marker selected. This allows the user to evaluate multiple signals simultaneously.

The similarly sized IFR 2399A offers a lower noise floor of -125 dBm; the improved noise floor enables the user to search for spurious signals that can be obscured by the noise generated by the instrument.

At about the size of a breadbox, these portable spectrum analyzers don’t quite fall into the hand-held category; however, it is unlikely that spectrum analyzers will ever drop to cell phone size. Harber notes, “We aren’t at the limit of size yet, but we will be soon. If the instruments get much smaller the user won’t be able to read what’s on the screen, and they will lose their usefulness.”

The IFR 2397 and 2399A are priced just shy of the $10,000 mark. The price tag on a spectrum analyzer correlates with its frequency range; the higher the range, the more the spectrum analyzer costs. Aeroflex’s new low-cost 26.5 GHz spectrum analyzer is priced at $24,900. It offers features similar to those found in the 2397 and 2399A. It also allows storage of up to 1,000 screen traces and 2,000 operational states.

A new analyzer with a large memory for storage of information and displays can be a great advantage, says Dennis Handlon, product manager for spectrum analyzers for Agilent Technologies (Palo Alto, Calif.). A new spectrum analyzer with a hefty memory can be a decent compromise for a biomedical engineering department that wants, but cannot afford, remote monitoring capabilities. The remote monitoring feature allows the spectrum analyzer to be connected to a LAN; then, by calling an Internet address, the user can monitor remotely.

“In the future connectivity is going to become more and more important, Handlon opines. “Buyers should look for a spectrum analyzer with a LAN port, and most of the new modern analyzers do have them.”

Agilent’s PSA Series spectrum analyzers include a wide array of connectivity features to measure, archive and analyze measurement results. Intuilink software allows the user to capture data and screen display from within Microsoft Word and Excel. Optional Benchlink Web Remote software allows the instruments to be controlled remotely by a PC from anywhere in the world through a Web browser.

The high-performance PSA series is just one of Agilent’s spectrum analyzer offerings. The company also markets an ESA-L series for basic performance, an ESA-E series for midrange performance and an 8650 EC series for super midrange performance.

While portability is certainly key in the hectic healthcare environment, ease-of-use should also rank high on the biomeds’ spectrum analyzer wish list.

“When you look at the multitude of spectrum analyzers available you have to consider a practical solution that fits the need and technical expertise of the operator,” Kropuenske advises. “Certainly ease-of-use would be a high priority, as an engineering lab-grade analyzer could easily overwhelm a technician if he uses it only periodically.” And for better or worse, most biomeds’ lives are not centered on spectrum analyzers.

According to Handlon, Agilent excels at designing easy-to-use products. “The novice user can get as good a result as the expert user with our spectrum analyzers. This company understands that these guys want results. They won’t be enamored by all of the bells and whistles if the product is not easy to use.” Consequently, Agilent’s PSA Series incorporates a lot of one-button measurement tools. Peak search, for example, can be completed with a single keystroke.

Lawrence Wilson, marketing manager for wireless products and signal sources for Tektronix (Beaverton, Ore.), says the company has focused on ease-of-use in its spectrum analyzer products.

 The NetTek over-the-shoulder spectrum analyzer from Tektronix

“We’ve spent a lot of time on usability and included intuitive, one-button measurements that allow the user to focus on the job, not the device.” The company’s NetTek Analyzer Platform is a hand-held field tester that features a Windows CE operating system. Common measurements are optimized, providing quick, repeatable results. User controls and buttons appear on screen only when they are needed, making it easier to complete measurements.

Tektronix has also attended to versatility in its product design. Wilson points out, “We try to give multiple capabilities in one box. Our customers don’t want a different piece of specialized equipment for each task.” NetTek features a modular design; users can customize the analyzer to meet their specific needs via various modules and options.

Another choice from Tektronix is the WCA200A series of wireless communication analyzers, which offer traditional spectrum analysis capabilities, real-time spectrum analysis and modulation analysis in one tool. The WCA 200A products were developed for designers and manufacturers of wireless components and devices and may be more tool than the average biomed needs.

Taking a Test Drive
Looking for that just right spectrum analyzer? It’s worth the time to do it right because it’s likely that whatever analyzer you choose will hang around for a while.

Take a few spectrum analyzers for a test drive to gauge their actual portability and user-friendliness. Find out what the in-house current and projected frequency range needs are. Determine if the hospital’s high-frequency devices are covered by service and maintenance contracts. Talk to other biomeds about their recommendations and experiences.

Finally, don’t overlook the manufacturers; they should be able to answer your questions and direct you to other BMET-customers.