Real-time analyzer software is designed for time-correlated multidomain analysis. This means a marker on a power-versus-time display can be made to time-correlate precisely with markers on the spectrogram and constellation displays. Timecorrelated markers improve diagnostic reliability by providing positive correlation between anomalies in different displays.
Phase-hits captured with the FMT can be positively time-correlated to symbol errors. The RTSA has made useful contributions in diagnosing challenging microphonic problems with its time-correlated markers and FMT. The RTSA technology also has found many successful applications with continuous signals that rapidly vary in frequency. The FMT easily captures phase-locked-loop synthesizer tuning transients.
Also, the RTSA offers captured and real-time I-Q data export capability. Real-time I-Q export is of particular interest to software-demodulator developers. Using a special port, today's RTSA can deliver I-Q data pairs to an external FPGA at bandwidths up to 36 MHz. So, software developers can construct and debug demodulators with reliable RF hardware, greatly speeding up the development process.
The RTSA is especially useful as a front-end digitizer for surveillance operations or as a test receiver for modulation research. Another special feature of the RTSA, from its surveillance roots, is a removable hard-drive for use in secure areas.
BASIC MEASUREMENTS Each of the three spectrum-analyzer types has unique abilities. Yet a great deal of capability overlap exists between them for basic measurements. Swept analyzers, VSAs, and RTSAs all compete directly with less demanding basic spectral measurements. VSAs and RTSAs have basic SA modes that emulate a traditional swept-tuned spectrum analyzer. Swept analyzers have made progress in offering high-performance vector signal analysis.
So, what considerations matter in picking the instrument most likely to get the best basic measurement data on the bench? When the special instrument capabilities discussed earlier aren't required, the goal is usually to provide the quickest diagnostic time-to-insight for the engineer. The faster a problem can be recognized, the shorter the engineering time required.
Human factors such as portability, size, weight, logical menu navigation, and setup time tend to be important for rapid time-to-insight with basic measurements. The industry has found that display versatility is a key ingredient in rapid and reliable troubleshooting. Multidomain instruments like the RTSA or VSA with spectrum, time-domain, modulation-domain, code-domain, and spectrogram views are more apt to provide conclusive diagnostics than older single-display swept analyzers.
The swept SA industry has raced to provide insight-enhancing displays on new models that go beyond the basic spectral information. Implementations range from clean lightweight portables to bulky multibox solutions. When the choice isn't so easy, designers might wish to consider the specialization of each analyzer.
INVENTORY MANAGING A good rule of thumb when selecting an analyzer that gets the best diagnostic insight for basic measurements is to consider the type of signal being measured.
The swept SA usually can be an effective tool for spectral measurements on pure analog signals, like an LO or analog modulation. The VSA may be useful in continuous digital modulations or twochannel measurements. And, the RTSA is usually preferable in intermittent or transient RF-signal applications. In recent years, virtually all of the most popular new wireless systems have taken on a transient nature, making the highest-productivity instrument the RTSA.
Unfortunately, many established RF companies find their spectrum-analyzer inventory loaded with older swept-tuned analyzers. In many cases, the older SAs' limited capability with today's popular transient RF signals warrants the addition of some RTSAs to rebalance the test equipment pool. Frequently, companies that want to participate in the explosive growth of WLAN, RFID, 3G, and other TDD systems find it necessary to retool their test resources to remain competitive. Each of the three basic types of spectrum analyzers was created and optimized to solve different problems. To get the most out of any spectrum analyzer, consider what type of signal will be analyzed. Understanding the key differences between today's spectrum analyzers lets designers match the analyzer type to signal characteristics, improving diagnostic efficiency.
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