EE’s electronic test instrument coverage achieved critical mass in the mid-1980s, including a spectrum analyzer story in the August 1986 issue and subsequent August issues into the 1990s and beyond. The 1986 article featured interviews with Data Precision, Scientific-Atlanta, and Solartron. At the time, modal vibration analyzers, dynamic signal analyzers, and audio analyzers made by these three companies as well as those from Shigma, Zonic, and Panasonic typically were grouped under the FFT analyzer heading.
RF or microwave frequency ranges distinguished the traditional swept-frequency spectrum analyzers made by Anritsu, Eaton’s Electronic Instrumentation Division, Marconi Instruments, Wandel & Goltermann, and Tektronix. Early Tek spectrum analyzer plug-ins for the 530/540 Series were developed by Pentrix, acquired by Tek in 1964. Also in 1964, Hewlett-Packard (HP) introduced the 8551A Microwave Spectrum Analyzer that set the performance standard for several years.
Hewlett-Packard Model 8551 Microwave Spectrum Analyzer c. 1964
Courtesy of Agilent Technologies
The August 1987 article confirmed that the term dynamic signal analysis was not yet closely identified with mechanical systems. The opening paragraph began, “Performing dynamic signal analysis on radar systems, communications equipment, CATV…” Nevertheless, it was well understood that RF/microwave measurements could be complicated, and an HP instrument was discussed that had more than 100 built-in measurements. A Tek representative described his instrument’s help mode, nonvolatile setup storage, macro programming, and CRT user prompt messages.
The 1987 article listed microwave spectrum analyzer manufacturers HP, Rohde & Schwarz, IFR, Tek, Advantest, and Eaton. And, a separate signal analyzer section featured a PC-based FFT analyzer from IQS with an “advanced vector signal processing architecture.” By 1988, a sufficient number of accurate measurement capabilities were included in a spectrum analyzer that an article questioned the continuing need for stand-alone instruments such as frequency counters or modulation meters.
“Exploring the Frequency Domain” ran in August 1989 and highlighted the increasing importance of FFT and parallel filter bank architectures for transient capture and analysis. According to a Tek document of the period, the update time was limited to about 20 ms for a complex 1,024-point FFT, making this technology suitable only for audio and modal analysis. The document explained that the company had developed a digitally implemented parallel filter bank technique with a 200-µs update period. Today, Tek’s range of real-time spectrum analyzers features 50x faster 3.7-µs FFT technology.
The 1990 article “Digital Implementations Compete With Swept-Frequency Analyzers” tackled the mismatch between the need to simultaneously capture all of a signal’s frequencies and the swept-frequency spectrum analyzer’s serial operation. FFT advantages were explained from the viewpoint of companies like LeCroy that did not make conventional spectrum analyzers but did produce DSOs with FFT capability. In contrast, only a swept-frequency spectrum analyzer could deal with hundreds of gigahertz, according to HP.
Many of the advances made during the next decades were predicted in the 1989 article. For example, HP’s Joel Salzberg thought modular instrumentation would continue to develop, giving the benefit of more flexible system configuration. And, IFR’s Tom Dideum looked for more spectrum analyzer enhancements via firmware and software.
The 1990s saw a gradual redefinition of the spectrum analyzer to take advantage of the best that both digital and analog design could provide. For example, virtually all modern spectrum analyzers implement narrow resolution bandwidth filters digitally, offering much faster and more precise performance than possible via analog techniques. A vector signal analysis option was available on some spectrum analyzers in the late 1990s, indicative of the growing importance of digitally modulated signals.
The 1998 article “When and How to Apply FFT-Based Spectrum Analyzers” and the 2005 “Understanding Noisy Signals” highlighted the benefits of simultaneous capture of all the frequencies composing a given signal. The 2005 article specifically considered dynamic signal analysis. An article in 2006 focused on advances in communications test equipment such as Anritsu’s MS2721A and Willtek Communications’ 9102, both handheld spectrum analyzers.
As the new millennium’s first decade drew to a close, it became obvious that the classic swept-frequency spectrum analyzer largely had been replaced. Often, the new instrument still was called a spectrum analyzer although the IF section was totally digital and several of the familiar displays were generated digitally to mimic traditional ones. However, vector signal analyzers better address the requirements of complex modulated signals, and these instruments will be featured in September’s 50 Years of Test Technology article.