Real-time spectrum analyzers reveal elusive glitches and other transient RF signals

The rapid development of digital radio frequency (RF) technology has resulted in an increasingly crowded and inefficient spectrum; at the same time, modern RF signals have become extremely complex. To improve capacity, performance, and confidentiality, sophisticated RF techniques such as bursts, frequency hopping, and adaptive modulation are generally used in combination, all of which exhibit time-varying power and frequency characteristics and transients. The interweaving and prevalence of these signals presents various challenges to design engineers who must capture and analyze these time-varying RF signals.

RF engineers need to see the accurate details of RF signals that change over time more than before, so Rick King, vice president of the RF test product line of Tektronix, pointed out: "Time can no longer be ignored in the RF field. Now is the time to use the next generation of real-time spectrum analysis technology." Relying on traditional swept spectrum analyzers and vector signal analyzers (VSA), engineers have not been able to capture and analyze these transient RF signals 100%. The latest RSA6100A series real-time spectrum analyzer launched by Tektronix enables engineers to quickly capture and analyze problems.

This series of products provides an excellent combination of capture bandwidth and dynamic range. The 6.2GHz RSA6106A and 14GHz RSA6114A provide the industry-leading 110MHz real-time bandwidth and 73dB spurious-free dynamic range, both of which are difficult to achieve in other products.

One of the key breakthroughs of the new product RSA6100A for high-end applications is the introduction of digital phosphor (DPX) technology. King said: "DPX waveform processor technology generates the industry's first real-time RF spectrum display, allowing engineers to view RF signal instabilities and transients that they never knew existed before. It greatly improves the spectrum update rate and information display capabilities, turning large amounts of RF data into a clear view."

DPX technology introduces the digital phosphor oscilloscope (DPO) technology in the time domain into the frequency domain. It uses a parallel processing structure, and its spectrum processing speed is nearly 1,000 times faster than the fastest swept spectrum analyzer and vector signal analyzer, and it can process more than 48,000 spectrum measurements per second. By continuously converting time domain signals to the frequency domain, DPX technology provides a means for displaying frequent events and infrequent events at the same time, extracting and calculating discrete Fourier transforms (DFTs) in real time at a frame rate far higher than that of the human eye, and converting them into intuitive and comprehensive activity pictures.

Variable color-grade persistence keeps anomalies visible until they can be seen, so Matthew J. Maxwell, product manager for Tektronix's RF product line, emphasizes: "The RSA6100A helps reveal elusive glitches and other transient events. At each update, the power level value at each frequency in the capture bandwidth is recorded and the color changes on the display to show how the signal power at each frequency changes over time." Spectral information below the peak amplitude of the time-varying spectral envelope can be revealed.

Another important aspect, RSA6100A provides a unique frequency mask trigger (FMT) function, which allows users to trigger measurements based on the occurrence of unique event patterns in the spectrum. FMT's high dynamic range can trigger weak transient signals while ignoring known strong signals. FMT works over the entire 110MHz real-time bandwidth of the RSA6100A series, reliably capturing difficult-to-detect RF signals or frequency anomalies that traditional analyzers would miss.

When debugging RF circuits, FMT is essential for finding low power or time varying signals. It can detect sporadic signals, the presence of intermodulation products, and transient spectrum suppression violations. FMT is essential for surveillance applications and radar work, as it can capture spectrally relevant events, such as weak signal pulses in complex spectral conditions, which cannot be captured by level-based triggering alone.

From the application point of view, Maxwell pointed out that RSA6100A is suitable for many fields such as digital pre-distortion (DPD) power amplifier, radio monitoring, radar design, etc. In view of the situation in China, Wu Youshou, professor of the Department of Electronic Engineering of Tsinghua University and academician of the Chinese Academy of Sciences, emphasized its significance for digital television: "The formulation of digital television standards has put forward the demand for real-time spectrum testing, and the digital television broadcasting standard will soon be used in China. How can digital television reliably receive signals under high-speed movement? How to ensure that interference is avoided in complex spectrum application environments? These application studies also require real-time spectrum analyzers."

Figure: Simplified block diagram of the RSA6100A Series

The RSA6100A's measurement-centric user interface is specially designed to not only optimize parameters for any measurement combination selected by the user, but also to manually adjust these control functions at any time. The RSA6100 series also includes the most frequently used functions in traditional spectrum analyzers, such as peak and mean detection, waveform averaging, maximum hold, minimum hold, reference waveforms, and resolution bandwidth filters in various operating modes. The RSA6100A series uses a 10.4-inch XGA touch screen display and provides mouse/keyboard and traditional front panel operation control functions. These instruments use the Windows XP operating system and provide a familiar user interface for common tasks, such as file management, printing, copy/paste, import/export, tools, help, and more.