Test / Data Acq.
Unwrapping Wireless Signals |
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Friday, 05 January 2007 |
Arbitrary waveform generators (AWGs) have become the standard signal sources for baseband and IF signals in wireless test applications. The increasing sampling speed, bandwidth, and linearity of available instruments are opening the door to direct RF generation. Although the instruments can generate high-quality signals, wraparound artifacts can ruin the final results. By using the right signal-calculation algorithms and techniques, you can eliminate wraparound problems while saving precious generation memory....more  (0) Comments |
Software-Defined Radio Architecture For Communications Test |
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Tuesday, 02 January 2007 |
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It seems that a new wireless or communications standard is introduced each day. Although this is not true, the list of wireless and communications standards is rapidly growing (see Figure 1). In the last few years, more and more standards deal with the increasing need and demand for data. We now face a log jam of standards. Just a few years ago, a single wireless technology per device was sufficient. Now, due to the number of standards existing at the same time, devices must implement multiple standards to compete by providing seamless operation across different networks and for differing applications. In this article, Spencer and Ron explain the advantages of devices that support multiple communications standards, and where these technologies are taking the industry....more (0) Comments |
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Tuesday, 02 January 2007 |
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A displacement or error referenced to a signal’s ideal timing is called jitter. For example, if the positive-going edges of a clock signal are used as the timing reference for a digital circuit, then any deviation of the actual clock edges from their ideal positions constitutes jitter. The reason for interest in jitter is because, at a sufficiently high level, it makes circuits fail. If a communications link, for example, must operate with only one error in 1012 b, a common specification, then the total jitter must be less than the amount of jitter corresponding to a 10-12 bit error rate (BER)....more (0) Comments |
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Another One Rides The Bus |
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Tuesday, 02 January 2007 |
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Data acquisition systems are available based upon a huge variety of interfaces. Ethernet, PCI, USB, PXI, PCI Express, Firewire, CompactFlash, and even the venerable GPIB, RS-232/485, and ISA bus are all popular. Which ones are the most appropriate for a given application may be far from obvious. Perhaps the first question to address when considering a new data acquisition project is whether your application is best served by a plug-in board system such as PCI or PCI Express or an external box-based system like Ethernet or USB. This issue has been a source of much confusion over the years, and the decision may be less well defined than ever today....more (0) Comments |
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Beware Of Spectrum Analyzer Power Averaging Techniques |
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Monday, 01 January 2007 |
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Averaging is a common technique for reducing the measurement uncertainty inherent in all measurements. Performing the same measurement a number of times and averaging the results can reduce the randomness of the experimental result. Averaging is an automatic function available in most instruments. Rather than returning noise-ridden results, an instrument may make 100 measurements, calculate the average, and return just that average as the measured result. But power averaging in spectrum analyzers may actually provide misleading data as the following experiments intend to show. The experiments involved correlating the power measurements of two spectrum analyzers from different vendors. However, the issues discussed are generic in the sense that they apply to any spectrum-analyzer power measurement with some form of post-detection averaging....more (0) Comments |
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LXI Leverages Ethernet For Test |
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Monday, 01 January 2007 |
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For decades, the venerable Hewlett-Packard-derived IEEE-488/GPIB (General Purpose Interface Bus) served well in small- and medium-sized test systems, with VXI-based testers meeting the needs of high channel-count applications. Time marches on. Test engineers now seek high-bandwidth systems that are relatively easy to configure and are low in cost. Some system architects are turning to USB (Universal Serial Bus), and USB certainly has a niche in test racks. Others use standards-based communications approaches and buses such as PCI and PXI, but LXI (LAN eXtensions for Instrumentation) is ascending beyond these implementations....more (0) Comments |
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