Software Enables Editing of RF Signal-Capture Files
By Jim Taber, Director of Sales and Marketing, X-COM Systems
The ability to digitize data near (or at) the antenna is obviously a huge benefit in applications ranging from electronic warfare and signals intelligence to laboratory, production, and field testing. It will continue to pay dividends long into the future as analog-to-digital converters (and vice versa) creep up higher in bandwidth. As they do, one of the greatest challenges will be how to analyze the massive amounts of data created over long-term signal captures, even with modest bandwidths. Fortunately, software tools are available that make it possible to identify, analyze, and modify waveforms or waveform segments or even entire files. In the process, the file size is greatly reduced to one that can be easier handled by PCs and workstations.
The task of identifying only those waveforms considered to be signals of interest falls to by X-COM’s Spectro-X signal analysis software, which uses four different types of search engines to find the files and then create a new file containing only the desired sections. Spectro-X (Figure 1) lets users simultaneously analyze up to four RF and microwave spectrum files at the same time with precision file alignment to plus or minus one sample, which dramatically reduces the time required to discover RF anomalies within a complex spectral environment or to evaluate signal characteristics over time. It also applies changes made to a marker in one domain to all other characteristics in that domain.
Spectro-X operates on files of signal activity captured over the air using an Agilent, Rohde & Schwarz, or Tektronix signal analyzers and X-COM’s IQC5000A Series RF Capture and Playback System. It can also use custom spectrum files created in MATLAB or other software.
The software’s four discrete search engines (carrier, wireless standard, arbitrary waveform, and pulse) allow signals of interest to be found rapidly, and users can zoom-in to specific sections of a file in frequency, time, or both, to find signals of interest. The results can be exported in a file format usable by vector signal analysis software such as Agilent’s 89600B or SignalVu from Tektronix for demodulation and detailed analysis. There is a wide range of characterization capability within Spectro-X for pulsed waveforms, including rise and fall times, pulse width, pulse repetition interval, peak and average power, and carrier frequency.
RF Editor software from X-COM Systems allows the user to trim, join, repeat, lengthen, delay, filter, or shift waveform segments in frequency, and to perform many other changes as well, on up to 10 independent tracks (Figure 2). The latest version of this drag-and-drop software, Version 3.0, works with files of any length that were obtained by either capturing signals over the air, offloaded from a signal analyzer, or created in software tools such as MATLAB. As RF Editor and Spectro-X are seamlessly integrated, the user need only transfer the file from Spectro-X to RF Editor where it is modified to the desired degree and then with a single mouse click to create a new, custom waveform file. The file can then be sent back to Spectro-X where it can be used for many purposes such as testing using the waveform sequence as a stimulus, and a variety of functions necessary in electronic warfare and signals intelligence.
RF Editor allows functions to be performed both sequentially and automatically, such as frequency shifting, file decimation, and bandpass filtering with bandwidths as narrow as 10% of a waveform segment’s span. Other features include presets for fast frequency shifting and span adjustment, power adjustment with 0.1-dB resolution, and the ability to apply frequency offsets, interference, and noise to produce a wide range of test scenarios ranging from ideal or theoretical conditions to worst-case scenarios.
RF Editor 3.0 adds new features to its predecessor while also being faster and easier to use. Perhaps the most important of these features, stitching (Figure 3), allows unwanted portions of spectrum-capture files identified in Spectro-X to be eliminated or replaced with data from a different file and then reconnected, producing files with only the desired characteristics.
The new group modify function significantly reduces the time required to modify the attributes of large numbers of signal-capture files, which previously had to be performed individually. The user now simply selects a group of files to be modified, indicates the desired modifications from the many choices provided by RF Editor (such as shifting frequency, resampling, filtering, or changing attenuation or gain), and the software will make the modifications without operator intervention.
The new software also now supports the .xdat file format used by X-COM’s VSG5000A multichannel signal generator and IQC5000A RF capture, recording, and playback system. These files contain much more information than standard .dat files, including markers, center frequency, span, sample rate, date, time, and GPS positional data. RF Editor 3.0 also includes scale factor calibration, which enables modifications to be made to the scale-factor parameter that RF Editor uses to determine signal power in order to add or subtract attenuation or gain. RF Editor 3.0 and Spectro-X software are available from X-COM and trial versions of each one are available on the company’s Web site.
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