Review: Tektronix RSA306 spectrum analyser (part 1)

Feature articles | December 2, 2014

By eeNews Europe

With the breakthroughs in components used for wireless technology, the size and weight of these instruments has decreased dramatically. This is good news for product designers whose workbenches may already be cluttered with other test instruments or for those like myself who work a lot in the field or travel a lot.

A few other manufacturers have pioneered the concept of PC-controlled spectrum analysers and Tektronix has recently entered the fray with its RSA306, which has dramatically raised the bar in terms of performance and measurement capability. The RSA306 is a well-built rubber-covered unit that is about the size that will slip into the jacket pocket of your suit (30 x 190 x 127 mm). It would also fit easily into a briefcase along with a 15-inch PC laptop. It is designed to meet MIL-STD-28800 Class 2 environmental, shock and vibration for use in harsh environments. The RSA306 is powered solely through the USB 3.0 port. The frequency range is 9 kHz to 6.2 GHz and can measure from +20 to -160 dBm (at minimum resolution bandwidth of 100 Hz). The unit can capture fast transient pulses with its 40 MHz real-time IF bandwidth. There are also external 10 MHz reference and trigger/sync SMA inputs, so you can sync to line frequencies, for example. The measurement input is an N connector with protective rubber cap. With all this, Tektronix has been able to keep the cost down to just €2,810 for the basic unit. Included in this price are a safety/installation manual, USB 3.0 cable and USB flash drive containing the documentation files, user manual, drivers and SignalVu-PC software.

Figure 1 The Tektronix RSA306 is a small rugged package that can easily fit into a briefcase, along with your laptop.

One reason for the low cost is that much of the functionality lies in the SignalVu-PC RF analysis software. The software includes 17 standard spectrum and signal analysis measurements, with several optional application-specific options available (€757, each). These options include mapping, modulation analysis, standards support (such as APCO P25 and WLAN), pulse measurements and frequency settling. The real time (DPX mode) can detect transient or intermittent signals as short as 100 µsec, which would aid in interference hunting. The software can also capture streaming and audio demodulation for long-term surveillance monitoring. Because the personality of the instrument lies within the software, upgrades and adding optional measurement capabilities are easy.

Figure 2 The RSA306 connected to a Mac laptop running Windows 8. The harmonics from an Arduino controller are being measured. The regular spectrum and waterfall are displayed.

Next page; PC host requirements

As you might imagine, the PC requirements are pretty stiff, as all the digital signal processing occurs there. Tektronix recommends a PC with at least the following specs: USB 3.0 port and 64-bit Windows 7 or 8 OS. For full support of the real-time features, an Intel i7 4th-generation processor and 8 GB of RAM is required. Storage of streaming data requires the PC be equipped with a drive capable of streaming storage rates of 300 MB/sec, such as most solid state drives. I tried using the RSA306 on my Macbook Pro with i7 Intel processor and 8 GBytes RAM with 500 GByte SSD running Windows 8.1 via Parallels 10 and everything seemed to run fine, but adding the DPX (real-time) mode did make the software choke. Running the unit with a high-end PC works fine, though. I suspect running a virtual operating system [within the Apple OS] slows the processing down too much.

Figure 3 The front panel of the RSA306 showing the measurement input, along with the 10 MHz reference input and Trigger/Sync input.

Installation of the software was made easy with the supplied USB flash drive and I was up and operating in short order. The layout of the software user interface (UI) was pretty straightforward. There are the typical menu bar along the top (File, View, Setup, Tools, etc.). The vertical scale controls are located along the left of the display and the horizontal scale, resolution bandwidth, trace, marker controls are along the bottom. Located under the main menu bar are the recording and replay controls indicated by standard record/play icons. As a part of the instrument turn-on, you need to link (“LiveLink”) the software with the RSA306. It would be nice if this was automated after the first time, but it seems to require a manual link-up each time the software is started. Otherwise, it took me just a few minutes to locate all the most important controls and I was making measurements without trouble. The UI may be controlled with either a mouse or touchscreen, if your PC is so designed.

The default display is the spectrum mode with a single trace. However, there are up to three traces that may be displayed, with separate controls for each. There is a Math feature that can subtract one trace from another and this fourth “Math” trace may be displayed, as well. There are five markers available and there’s also a spur detection mode, which records all spurs between 9 kHz and 1 GHz that are above a specified threshold (default setting) and the upper limit may optionally be increased to 6.2 GHz (full band). This would be ideal for quickly identifying a series of harmonics, where just the top several could be recorded. There are six trace detection modes: +Peak, -Peak, ±Peak, Average (VRMS), Average (of logs), and Sample (described below). Trace processing includes Normal, Average, Max Hold and Min Hold. Traces may be saved and recalled for display later or saved to a file. Instrument setups may also be saved and recalled.

Figure 4 Spectral plot showing several harmonics from the Arduino controller. This also shows the layout of the user interface.

Next page; modes and displays

The available detection methods (depending on the display mode) are:

+Peak – The highest value is selected from the results to be compressed into a trace point.

-Peak – The lowest value is selected from the results to be compressed into a trace point.

±Peak – Both the highest and lowest values are selected from the results to be compressed into a trace point.

Avg (VRMS) [Average VRMS] – Each point on the trace is the result of determining the RMS Voltage value for all of the results values it includes. When displayed in either linear (Volts, Watts) or Log (dB, dBm), the correct RMS value results.

Avg (of logs) – The detector is used to emulate legacy spectrum analyser results and for the specification of DANL (displayed average noise level), which allows a fair comparison to other spectrum analysers. In older swept analysers, a voltage envelope detector is used in the process of measuring signal level, and the result is then converted to Watts and then to dBm. Averaging is then applied to the resultant traces. For CW signals, this method results in an accurate power measurement. However, with random noise and digitally modulated carriers, errors result from this ‘average of logs’ method. For random noise, the average of logs methods results in power levels -2.51 dB lower than that measured with a power meter, or with a signal analyser that measures the rms value of a signal, and performs averaging on the calculated power in Watts and not dBm or other log-power units.

Sample – The first value is selected from the set of results to be compressed into a trace point.

CISPR Peak – The trace value is calculated by the methods described for peak detectors in the CISPR 16-1-1 documents.

There are seven filter shapes available, depending on your measurement needs:

– Kaiser (closest to traditional Gaussian)

– -6 dB MIL (required for MIL-STD-461 measurements)

– CISPR ( complies with CISPR 16-1-1 for EMI measurements)

– Blackman-Harris (good side-lobe level)

– Uniform (best frequency resolution, but poor amplitude accuracy)

– Flat-Top (best amplitude accuracy, but poor frequency resolution)

– Hanning (good frequency resolution).

There are several display modes that can be dragged from the Display Section window to be used for measurements. The base unit includes the following:

General Signal Analysis	Description
Spectrum analyser	Spans from 100 Hz to 6.2 GHz, 3 traces + math and spectrogram trace, 5 markers with power, relative power, integrated power, power density and dBc/Hz functions.
DPX Spectrum/Spectrogram	Real time display of spectrum with 100% probability of intercept of 100 µsec signals in up to 40 MHz span.
Amplitude, Frequency, Phase vs Time, RF I and Q vs. Time	Basic vector analysis functions.
Time Overview/Navigator	Enables easy setting of acquisition and analysis times for deep analysis in multiple domains.
Spectrogram	Analyse and re-analyse your signal in 2-D or 3-D waterfall display.
AM/FM Listening	Hear and record to file FM and AM signals.

Analogue Modulation Analysis	Description
AM, FM, PM analysis	Measures key AM, FM, PM parameters.

RF Measurements	Description
Spurious Measurement	User-defined limit lines and regions provide automatic spectrum violation testing across the entire range of the instrument.
Spectrum Emission Mask	User-set or standards-specific masks..
Occupied Bandwidth	Measures 99% power, -xdB down points.
Channel Power and ACLR	Variable channel and adjacent/alternate channel parameters.
MCPR	Sophisticated, flexible multi-channel power measurements.
CCDF	Complementary Cumulative Distribution Function plots the statistical variations in signal level.

Optional displays include:

• General purpose digital modulation (Option SVM)

• OFDM Analysis (Option SVO)

• P25 Analysis (Option SV26)

• Audio Analysis (Option SVA, this includes detailed AM/FM/PM measurements including SINAD, and audio measurements of the demodulated signal including THD. Direct audio measurements are also possible at >9 kHz audio frequencies)

• WLAN analysis (Options SV23, SV24 and SV25). These provide standards-based measurements of 802.11a/b/g/p, 802.11n and 802.11ac respectively.

• Pulsed Analysis (Option SVP)

• When option MAP (Mapping and Signal Strength) is installed, the Signal Strength measurement appears in the RF Measurements folder.

• When Option SVT is installed, frequency and phase settling plots populate RF Measurements folder

next page: hands-on measurements and summary

Continuing with some hands-on measurements, I tried measuring the harmonics from my Advanced Electromagnetic Technologies (AET) USB-S-1.8432 comb generator from 10 kHz to 100 MHz as well as my 915 MHz TriSquare frequency-hopping spread spectrum radio. I also added the Spectrogram (waterfall) display, trying out both the 2D and 3D modes.

Figure 5 A display of my AET USB 1.8432 MHz comb generator with spectral and 3D spectrogram displays. The 3D display can either face left or right.

Figure 6 The spectral and 2D waterfall displays of my 915 MHz frequency-hopping spread spectrum hand held radio. The spectral plot has some built-in delay showing the hop frequencies gradually decaying in amplitude.

In summary, I’m totally impressed with the rugged quality of the RSA306 and the functionality Tektronix has built into the SignalVu-PC software. This is the USB analyser other manufacturers will need to target as far as price and performance. The RSA306 is a relatively low-cost analysis solution for companies who wish to perform pre-compliance testing or EMI troubleshooting of their products prior to formal compliance testing. I can also see it used in university settings (the unit includes a security slot [a.k.a. Kensignton lock]) or training seminars and for applications, such as wireless troubleshooting or hunting down interference to communication systems. Highly recommended!

In Part 2 of this review, I’ll cover more advanced measurements, including real-time measurements, WLAN, modulation analysis, etc.

About the Author;

Kenneth Wyatt is an independent consultant and specialist in electromagnetic compatibility (EMC) design, test and troubleshooting. One specialty is his use of do-it-yourself probes and use of low-cost test equipment and measurement techniques for evaluating EMC issues on the workbench.

For more information:

Tektronix RSA306 web page
RSA306 data sheet
RSA306 user manual
RSA306 on-line demo
Real-time spectrum analysis for EMI diagnostics (Tek)