How to Make Spurious Emissions Measurements

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Transcript: Spurs outside of your device’s assigned operating channel can be problematic. They can even cause your device to be rejected by regulatory agencies. Today we’ll look at how to measure spurious emissions, which helps you evaluate your device’s performance and determine whether or not you’ll pass emissions regulations.

In this video, we’ll be looking at how to measure spurious emissions.

Oscillators and transmitters generate non-harmonic, low-level spurs. Collectively, those unwanted spurs generated outside of the assigned channel are called spurious emissions. This unwanted stray frequency content can appear both inside and outside of your device’s designated bandwidth. But, with spurious emissions testing, we really only care about the ones outside of your device’s designated bandwidth.

Looking at these two traces on the screen here we see a 1 MHz span at 935 MHz. If you look closely at the trace on the right then you can see the presence of an unwanted spur that can prove to be quite troublesome.

Spurious emissions testing is usually performed post R&D during design validation and manufacturing. Agencies like the FCC in the US and ETSI in Europe place strict limits on spurious emissions, so to make sure you are meeting these standards, it is imperative to monitor the spurious signals from your device.

What can be frustrating is that finding spurious emissions manually is an extremely time-consuming task that can potentially take days to complete.

That’s fine if you’re only doing this a few times a year, but if you’re doing this regularly, you can save a lot of time by using a signal analyzer with a spurious emissions application.

For example, for this signal, we can see the analyzer has identified some spurs. This saves you from having to hunt for each spur manually.

This analyzer can also display a limit line for the maximum emissions according to the communications standard you are trying to meet. If any of the spurs fail, you’ll see a fail indicator here and a fail next to that spur in the table.

When measuring spurious emissions, you should also consider the noise floor of your signal analyzer. If it’s too high, you won’t be able to see low-level spurs.

Knowing what spurious emissions are coming from your device will help you ide ... https://www.youtube.com/watch?v=38pDC09QSP0