Keeping Up: Dealing with Tricky Signals and Complex Standards

Blog Post created by benz on Nov 15, 2016

  Honing your engineering skills and staying alert for serendipity

The signals we deal with continue to become more complex and challenging. So do the standards that govern them and the measurements those standards specify. It’s a trend that shows no sign of slowing, and perhaps it’s some comfort that this trend is a source of intellectual adventure and job security. That’s the positive spin on it anyway!

Even single-domain spectrum measurements such as ACPR can evolve to a sobering complexity. Compare the W-CDMA and LTE-Advanced measurements below.

W-CDMA ACLR ACPR measurement

LTE-A cumulative ACLR CACLR measurement

The W-CDMA ACLR measurement (top) compares an active channel with two adjacent and alternate channels. The cumulative ACLR (CACLR) measurement (bottom) is considerably more complex, combining the power of multiple, non-contiguous carriers in a carrier aggregation configuration.

While tools such as measurement applications in signal analyzers help deal with the complexity of these measurements, they won’t handle all your needs for non-standard signals, troubleshooting, and custom measurements for components and manufacturing tests.

More often than not, finding all the measurement information you’re going to need involves an in-the-moment mix of trusted sources and geeky serendipity. Louis Pasteur’s famous quote comes to mind: “Fortune favors the prepared mind.” In this case, our “preparation” includes intentional and accidental encounters with application notes, books, blogs, symposium presentations, Web searches, and magazine articles.

I’ve been thinking about magazine articles because they cover both ends of the time scale that are important in making good measurements: classic measurement wisdom and techniques for handling the newest signals.

Under the heading “classic wisdom,” I was recently looking for the power-integration equation used for band power in a signal analyzer, vital for measurements such as those above. I found it in one of a series of articles by Bob Nelson at Microwaves & RF. Bob’s articles cover some classic or evergreen topics, and in this case he explains important points about measuring noise or noise-like signals.

By chance, the same day I started drafting this post, I received an email with a link to another of Bob’s articles on an evergreen topic, understanding measurement uncertainties. He not only describes the uncertainties, but gives an example of how to use extensive analyzer specifications to get the best performance in a specific situation. I have looked at this from a different angle myself, here on this blog.

Of course, the “latest and greatest” end of the time scale deserves just as much attention from magazine editors. Articles from experts with access to lots of test equipment provide timely explanations of measurements and usually add important context. Their guidance is even more valuable when the article also contains a list of references or links to related content. Expertly curated pointers are worth a lot, helping me avoid missing something important.

Worrying about missing something important is what keeps me alert to chance encounters with useful information: sometimes I don’t know what I don’t know. I pay special attention to things that would be counter to my assumptions or intuition because they are the source of errors I won’t even be watching for.

In the area of signal analysis, Keysight is starting to collect a foundation of measurement information on one page, starting with the fundamentals of signal analysis. Along with the other sources of information—and some serendipity—it can help us keep up and keep out of trouble.