One of the questions we often hear from customers is how a Tektronix real time spectrum analyzer such as the RSA5000 Series compares to a traditional spectrum or vector signal analyzer for capturing and analyzing signals. Since there are a significant number of distinguishing features I thought this would be a great topic for a blog post where I can go into a bit more depth.
Tektronix RSAs provides all of the features and capabilities of a conventional spectrum analyzer, a real time spectrum analyzer, and a wideband vector signal analyzer. However, unlike other instruments which force you into specific “modes” of operation (spectrum analyzer mode, real time mode or vector signal analysis mode), these features and capabilities can all be intermixed simultaneously – no mode switching needed. This is just one example of how the RSAs are different. Now let’s look at some of the other important distinguishing features.
RSA vs. Spectrum Analyzer
One very compelling difference compared to traditional spectrum analyzers is speed – particularly when making time consuming measurements like harmonic and spur searches. These typically involve scanning of a wide frequency span with very narrow RBW (resolution bandwidth) filters. This can take quite a long time on a conventional analyzer due to the need to sweep very slowly to avoid missing anything as well as giving the narrow filter enough time to charge.
For example, a 1GHz frequency SPAN with a 1kHz RBW will often take 20-40 minutes to sweep on a conventional spectrum analyzer. On an RSA5000 for instance, this literally takes just a few seconds. Furthermore, a multi-range sweep can be setup so that only frequency ranges of interest are swept rather that one contiguous span (which may sweep through areas of no interest, which wastes time). In this multi-range sweep, each range can have its own RBW, filter, detector, threshold, pass/fail criteria, making it very easy to complete complex harmonic and spur tests in one pass.
The real time spectrum analysis on Tektronix RSA instruments far exceeds any other real time analyzer on the market. It can be configured to process and display as much as 3.125 million spectrum measurements per sec in spans up to the maximum instantaneous bandwidth of the instrument, 165MHz in the case of the RSA5000.
The real time spectrum display can also be swept over any user desired frequency span, giving unprecedented visibility of transient activity from a single sweep. The user has full selection of RBW (not tied to span, etc.) in the real time mode. Real time analysis includes gapless spectrogram capability, as well as real time Zero Span, real time Frequency or Phase deviation vs. time.
RSA vs. conventional vector signal analyzer
Traditional wideband (>40MHz) vector signal analyzers force you to bypass the microwave pre-selector when operating above a given center frequency. This is because the pre-selection is done with a tunable YIG filter, and these filters have limited bandwidth. The problem with bypassing the pre-selection filter is that this opens several spectral “windows” that can (and do) allow out of band signals to convert into the first IF, and thus become indistinguishable from the true signal of interest. Tektronix employs switched bandpass filters instead of using a YIG, thus providing fully preselected operation over the entire frequency range and acquisition BW of the instrument. Tektronix RSA instruments are the only wideband vector signal analyzers to provide this advantage.
Triggering
Leveraging the power of the real time processing engine, as well as Tektronix’ 60+ years of triggering expertise with oscilloscopes, the RSAs feature the most powerful and flexible triggering capability in any real time signal analyzer offered today. This includes the basic triggers that are common to vector signal analyzers (external trigger, RF power level trigger and so on) as well as triggers common to real time analyzers (frequency mask trigger). In addition, the RSA features spectral density trigger (a very powerful trigger that lets you trigger on the spectral occupancy percentage changes visible in the real time spectrum display) as well as things like frequency edge trigger and runt pulse trigger to name a few. Regardless of the trigger event selection, additional time qualifiers can be added to further discriminate the particular event of interest.
Acquisition memory
RSAs can be configured with up to 4 GB of capture memory, the most in the industry. This translates to over five seconds of seamless IQ capture over the 165MHz maximum acquisition BW. The unit can also be configured to stream seamless IQ data out of the back of the instrument into RAID storage devices, for seamless wideband IQ capture for hours. Acquisitions can also be setup using segmented memory (fast frame), which can dramatically increase the “effective” capture time for acquiring low duty cycle events.
Vector Signal Analyzer features:
A full complement of vector signal analysis displays are also at your fingertips (operating simultaneously with the conventional spectrum measurements and real time measurements). These include basic vector signal analysis views such as amplitude, frequency, phase and IQ vs. time. Analog (AM/FM/PM) modulation analysis and baseband displays are available. For general purpose digital modulations, measurement displays including constellation, EVM, eye diagram, symbol table, and more. There are several standards specific analysis packages including 802.11a/b/g/j/p/n/ac, APCO P25, and Bluetooth BR/EDR/LE. Support for additional radio and wireless standards are continually being developed. Each of these includes an extensive selection of measurement displays including OFDM constellation, EVM, symbol table and packet summary. For Pulsed RF applications, there is a comprehensive pulse measurement suite that automatically characterizes up to 27 parameters of pulsed RF signals, and displays these results graphically and in table form, including pulse-by-pulse results as well as trends and statistics.
Frequency Range
The current RSA family goes up to 26.5GHz frequency range. However, all of the spectrum and vector signal analysis features are also available (with the same user interface) on any of the wideband real time oscilloscopes – which are available with up to 70GHz of analog bandwidth. The SignalVu Vector Signal Analysis measurement option is essentially the same software and user interface that runs the RSA, and is available to install and run on Tektronix windows-based scopes. This gives you essentially up to 70GHz of spectrum and vector signal analysis bandwidth. Further, when running SignalVu you still retain operation of the scope, allowing you to make time-correlated measurements between the different domains and take advantage of the extensive triggering on the scope.
Put it all together and you’ll see that the differences between Tektronix real time spectrum analyzers and traditional instruments are significant. What’s important to note, however, is that the RSAs aren’t different for the sake of being different – they are different in ways that improve measurement efficiency and accuracy and boost user productivity. Questions? Post them up in the comments below or drop me a line. You can find details on our full spectrum analyzer line up here.