What is Spectrum and Spurious Emissions – What the RF (S01E03)

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In this episode of What the RF (WTRF) Nick discusses what spectrum and undesired, out of band spurs are.

Transcript: In today’s episode, we’ll discuss in more detail what exactly a signal analyzer measures and the very important spurious emissions measurement that many of us will be making post R&D.

Alright, so from the previous episodes we know that signal analyzers are great tools to use for a holistic picture of our device’s signal.

But what exactly are we measuring on our signal analyzer?

We’re measuring spectra. Spectrum is comprised of a collection of sinusoidal waves and with a signal analyzer, we can measure the power of the spectrum of known and unknown signals.

Now with our signal analyzers, we can measure the frequency, power, distortion, and out of band emissions.

One such important out of band measurement is the spurious emissions measurement. This measurement helps you detect non-harmonic, low-level spurs that are most commonly generated by oscillators and transmitters of your system. Signal analyzers with low-level noise floors are sensitive to very low signals like spurs. This sensitivity is good because that means that we can actually see any spurs caused by our device and they’re not buried in the noise.

With the spurious emissions measurement, we can validate that our device is not emitting its remnant signal power into channels in which it’s not assigned to operate in.

Regulatory bodies like the FCC in the US and ETSI in Europe place strict limits on spurious emissions.

To give you an idea of what issues spurious emissions can cause let’s look at our signal analyzer here where we’ve now set the center frequency to 100 MHz and the span to 10 MHz. By connecting this antenna to the RF input of my signal analyzer we can see these distinct signals. We can safely assume that these signals are local radio stations, but let’s confirm that.

With this portable speaker, I’m going to connect it to the analog jack here and use the analog-demodulation app on our signal analyzer to see if we can confirm what signal this is.

Oh wow! Would you look at that, looks like it is a local radio station after all.

Let’s look at a real situation wher ... https://www.youtube.com/watch?v=SvS-Yd2Ed_U