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Tektronix RSA306 USB Spectrum Analyser - Review

Supplier: element14 By: Lui Gough
14 April, 2015

I would like to thank Tektronix and element14 for being so generous in providing the kit and choosing me as the RoadTester for this product. As usual, this is going to be a thorough and impartial review.

RoadTest: Tektronix RSA306 USB Spectrum Analyser

Evaluation Type: Independent Products

Application you used the part in: Signal Identification and Analysis, Fieldwork, Wireless LAN 802.11 testing

Was everything in the box required?: Yes - although, you will need to ensure you have already purchased whatever antennas and probes are necessary, along with adapters for the N-connector.

Comparable Products/Other parts you considered: Hobby software-defined-radios (SDR) such as RTL-SDR, Nuand BladeRF x40, Winradio G31DDC

What were the biggest problems encountered?: Some software options are placed in slightly counter-intuitive positions, and automatic acquisition and analysis settings are sometimes not sufficient to get multiple displays functioning simultaneously.

RoadTest Review: Tektronix RSA306 Real-Time Spectrum Analyser


I hope you all enjoy this review, which I have put in a lot of time in creating. This is a highly sophisticated package, which means that there is lots of ground to cover. I've tried to present it in the most logical progression, although in reality, some of the experiments and tests were not done in the order presented.

My initial plan was to review it over the new-year break, but that was not possible because of the shipping schedule (items received 2nd February 2015). I was somewhat under-prepared with this one, as I am more an RF-enthusiast in the short-wave listener, ham and satellite sense with access and knowledge about many different signals on the air, and had less experience with spectrum analysers. I lost some time in ordering and waiting for adapters and antennas to arrive. Furthermore, continuing commitments with my PhD research in writing papers meant I wasn't quite able to perform as many experiments as I would have liked.


In the past decade, the area of radio communications has been forever changed by the reasonably priced availability of high-rate analog-to-digital converters and digital-to-analog converters, along with a wealth of digital signal processing power enabled by the CPUs in modern computers. This ushered in the era of the "software defined radio" which allows us to emulate some of the the physical, analog components of a radio, such as filters, mixers and detectors, in the digital domain.

A software defined radio receiver generally minimises the analog domain to the signal conditioning required to isolate the bandwidth of interest and provide it in a format suitable for encoding by an analog to digital converter -commonly used components include, bandpass filters, impedance matching transformers and variable gain amplifiers. The high-rate digitised data is then processed by a computer to perform the "demodulation" itself.

Such a design, while initially quite difficult to implement due to high DSP computation requirements, proves to have several advantages over analog radios and front-ends, by allowing for the monitoring of a wider bandwidth in real time, enabling the implementation of ever-higher-bandwidth modulation modes with sophisticated forward-error correction and equalisation features, as well as freeing us from the bulk, imperfections and drift experienced by analog components.

When I first started with software defined radio back in 2010, I had invested a hefty sum (as a student) into a Winradio G31DDC 0-50Mhz USB 2.0 receiver. This unit offered continuous monitoring of just 2Mhz of spectrum at 16-bit resolution in its "digital IF" over the USB 2.0 link, and it required the best dual-core CPUs available at the time to achieve this. Regardless of the initial frustrations, I still use this unit today as a short-wave listener, utility monitor and ham alike, and it's relatively "easily" handled by modern equipment. This SDR was nothing short of a revelation - I could examine a whole 2Mhz band of channels at once, in real-time, and I could record the whole band and play it back at any time - re-tuning into any "narrowband" channel within this range. I didn't have to sit behind an old fashioned radio's VFO, tuned into a quiet channel, wondering if there was some action elsewhere across the band.

The recent popularisation of the RTL-SDR, based around the RTL2832U USB DVB-T TV Tuner chipset, shows just how useful the SDR concept is, even with only 8-bits resolution and about 2.4Mhz of spectrum available. Real-time ADSB aircraft monitoring, formerly very difficult due to the bandwidth requirements of 1-2Mhz, were now in reach of the average person. More importantly, this one was cheap, and accessible to many, with frequency ranges of about 70-1200Mhz (more or less depending on your front-end).

All of this action has resulted in a wide range of SDR-based devices, most of which are aimed at the hobbyist, and do not offer a guaranteed flat-pass-band, lack of signal images or response linearity. Naturally, such a design would be very applicable for test equipment as well, which are needed to keep up with the new wide-band modes which are becoming more common, but impose much more stringent requirements on the implementation. This has ushered in a new age of "real-time software defined" spectrum analysers.

Features, system requirements and important documentation

Traditional spectrum analysers can be thought of as very similar to a traditional analog radio, which is swept over a range of frequencies of interest, producing a plot of the detected signal power at a given frequency. Such an approach has many disadvantages, mainly due to the accuracy of such an analog front-end detector when it comes to sweep response at high sweep rates, and the fact that you will miss or distort short transient burst signals because you're not really looking at the whole spectrum all the time. Furthermore, with very old spectrum analysers with limited memory capabilities, your ability to analyse such captured signals may be limited to a set of basic measurements offered by the unit itself (e.g. markers) and any screen-captures you might be able to get. With more and more demanding digitally-based RF applications in radar and wireless communications, such issues can make proper measurements very difficult, frustrating or impossible to make.

Another consideration is the size and bulk of traditional bench-top units which make them less suitable for field work and interference hunting/direction finding. Early attempts at small, hand-held units tended to feature much poorer specifications, especially when it comes to bandwidth and screen resolution because of the need to squeeze numerous analog components into small cases and compromises in the design making them more difficult to use effectively.

The Tektronix RSA306 tries to bring the advantages of SDR-like technologies into a "software defined instrument". It leverages the SignalVu-PC application along with its measurement options, which has been used with their high end oscilloscopes (MDO/MSO) to do spectrum analysis, but offers it at a much more compelling price of US$3490 from Newark/element14. Instead of providing you a "whole" oscilloscope, you get a 3.5" hard-disk sized external unit, which connects to your computer via USB 3.0 and uses your computer to do all the analysis and display.

The RSA306 unit itself has a frequency range of 9khz to 6.2Ghz, from +20dBm down to -160dBm. It utilises a 14-bit 112MS/s analog to digital converter to perform its sampling, an FPGA to perform data manipulations, a Cypress Semiconductor bridge chip to move the data over USB 3.0 and provides a 40Mhz real-time spectrum display. The RF connection is made via a 50-ohm N-type connector, with two SMA connectors for trigger and external 10Mhz frequency reference input. Connection to a computer is by a USB 3.0 connection, which also supplies power to the unit. Teardowns of the unit have been performed by KF5OBS and is further discussed elsewhere, where disagreements on the interpretation of the internal design still persist.

With such a high-specification device, pushing in excess of 224MiB/s of data to your computer for analysis, the system requirements are suitably high. It is recommended that you use a system equipped with an Intel Core i7 4th-generation CPU, SSD storage for streaming recording (>300MB/s write), 8Gb RAM, USB 3.0 and Windows 7 or above, 64-bit edition. The unit will function with machines with slower CPUs but analysis may be more limited and it may affect the probability of intercept, and you will lose the streaming recording if you use a slower storage device. However, 8Gb RAM, USB 3.0, and 64-bit Windows is NOT negotiable, so if you don't already have a PC of sufficient specifications, you should factor it into your purchasing decision as well.

The unit and software was somewhat mysterious to me at first, as I had many questions which took some digging to answer. Tektronix currently has a range of very useful documentation for the RSA306 available by searching RSA306 in their manuals site and elsewhere on the site. I recommend users and prospective owners to read it all (as I have done), as some information isn't quite where you might expect it - but it's there!

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