Portable spectrum analysis

Carry Spectrum Analysis with You

Claims are that spectrum analyzers in portable form still sustain the high performance of their benchtop brethren. I got the chance to test-drive one to see if that’s really the case.

A rapidly growing trend within the RF/microwave industry is the portability of test equipment. Such is the case with the spectrum analyzer, which now can be found in various handheld sizes. Today, several different test-and-measurement suppliers offer USB-based spectrum analyzers. Let’s take a look at one product that exemplifies this trend.

Tektronix is fully on-board the portability train, providing test equipment such as the RSA306B—a portable, USB-based, real-time spectrum analyzer. The RSA306B covers a frequency range of 9 kHz to 6.2 GHz and has a measurement range of ‒160 to +20 dBm. It also is equipped with an acquisition bandwidth of 40 MHz. Moreover, a USB 3.0 cable comes included, so that the analyzer can connect to a laptop or desktop computer. The host computer provides all power, control, and data signals over the USB 3.0 cable.

The RSA306B operates with Tektronix’s SignalVu-PC software, which allows signal analysis to be performed on a laptop or desktop computer. Of course, a traditional benchtop spectrum analyzer has a display, as well as a range of buttons, for user interfacing. When operated with the RSA306B, the SignalVu-PC software essentially equips one’s computer with the display capabilities and user interfacing found on a typical spectrum analyzer.

Wide Range of Options

The RSA306B together with SignalVu-PC can perform a multitude of measurements. The free base version of SignalVu-PC offers spectrum analysis, RF power and statistics, and spectrograms. It also allows for amplitude, frequency, and phase-versus- time measurements.

Furthermore, the base version of SignalVu-PC can be enhanced by purchasing any of the advanced measurement options offered by Tektronix. The various options add different measurement capabilities, such as digital modulation analysis, pulsed RF signal analysis, wireless-local-area-network (WLAN) measurements, LTE measurements, Bluetooth measurements, and more. In essence, customers can choose the options they want to accommodate their specific needs.

A Firsthand Look

Tektronix loaned me an RSA306B, so I was able to get a better sense of what it can do (Fig. 1). Of course, the first step was to install the SignalVu-PC software. Fortunately, installation was quick and painless.

1. The RSA306B spectrum analyzer connects to a computer via a USB cable.

Once SignalVu-PC was installed, I was able to get started with the RSA306B. Using SignalVu-PC to view a spectrum-analyzer display on a computer is obviously a new experience for anyone who had previously only worked with benchtop analyzers. However, SignalVu-PC feels very much like a typical spectrum analyzer.

Figure 2 shows a SignalVu-PC spectrum-analyzer display of a 1.25-GHz continuous-wave (CW) signal. Here, it can be seen that the Frequency, Span, Reference Level, and Resolution Bandwidth parameters are easily accessible. In essence, those using the RSA306B with SignalVu-PC for the first time should become acclimated very quickly.

2. Illustrated here is a SignalVu-PC spectrum-analyzer display of a 1.25-GHz signal.

Pulsed RF Signal Analysis

After looking at some CW signals—which is obviously no big deal—I decided to experiment with some of the more advanced options. One in particular was the Pulsed RF measurement option.

It should be noted that each additional measurement option contains various display choices that users can add one-by-one to their assortment of selected displays. The Pulsed RF measurement option contains three display choices: Pulse Statistics, Pulse Table, and Pulse Trace. Users can analyze a number of pulse characteristics including Average ON Power, Peak Power, Average Transmitted Power, Pulse Width, Rise Time, Fall Time, and more. The Pulse Table display allows users to view whichever pulse measurements they choose in a spreadsheet format.

3. Shown is the pulse width of a 1-GHz pulsed RF signal along with a spectrum-analyzer display.

Figure 3 shows the Pulse Trace display alongside the basic Spectrum display. In this case, a 1-GHz pulsed RF signal is observed. The pulse width is set to 5 µs and the pulse period is set to 0.05 ms. Simply put, the Pulsed RF option provides users with a great deal of insight when analyzing pulsed RF signals.

Digital Modulation Analysis

Next, I decided to experiment with the General Purpose (GP) Digital Modulation analysis option, which essentially equips the RSA306B with vector-signal-analysis (VSA) capability. The GP Digital Modulation option contains a number of available displays, such as Constellation, Demod I&Q vs. Time, EVM vs. Time, Eye Diagram, Frequency Deviation vs. Time, Magnitude Error vs. Time, Phase Error vs. Time, Signal Quality, Symbol Table, and Trellis Diagram.

Figure 4 shows a constellation diagram of a 2-GHz quadrature phase-shift-keying (QPSK) signal. Also illustrated in the figure is the Symbol Table, which displays the information in a table format.

4. SignalVu-PC can analyze digitally modulated signals, such as this 2-GHz QPSK signal.

Conclusion

The RSA306B packs a great deal of measurement capability into a spectrum analyzer that can be held in one hand. This article only covers a fraction of the measurement capabilities offered by the instrument. However, I can certainly attest that the RSA306B is a product that delivers serious performance, and is worth a look for those in need of spectrum analysis on-the-go.

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