In this episode we'll be discussing what spectrum is and what undesired, out of band
spurs are.
My name is -
WHAT THE
What's up everyone!!
The name is Nick Ben and I'm an engineer here at Keysight and welcome to the 3rd
episode of What the RF!
In the last episode we discussed the difference between the time domain and frequency domain
and how measuring signals in each has their own advantage.
Click on the card above to see it.
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 in our product development cycle.
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.
On the signal analyzer our signals appear as distinct peaks over various frequencies.
But what exactly are we measuring on our signal analyzer?
We're measuring spectra.
Spectrum comprises of a collection of sinusoidal waves and with a signal analyzer we can measure
the power of the spectrum of known and unknown signals.
Signal analyzers at their core are receivers and their input is electrical signals.
Now with our signal analyzers we can measure the frequency, power, distortion, and out
of band emissions that are not easily detectable in the time-domain.
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, so to make sure you are meeting their standards, it is imperative to monitor
the spurious signals from your device.
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.
I will put the trace to max hold so we can see these signals more clearly.
We can safely assume that these signals are local
radio stations, but let's confirm that.
Why thank you.
Using 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.
With the analog-demod app we have 4 different screens that tell us useful things about our signal.
The RF spectrum, the demod waveform, the AF spectrum, and some useful statistics.
Oh wow!
Would you look at that, looks like it is a local radio station after all.
Let's look at a real situation where a spur can be problematic with this setup that
I have here.
I've connected two antennas, one to the RF output of the signal generator and another
to the RF input of the signal analyzer.
Let's use the signal generator to emulate a device that hasn't been checked for spurious
emissions, and as a result will emit in a bandwidth where it shouldn't be.
With the signal generator I can create an artificial spur, or rather a signal,
at the same frequency that we heard that local radio station on earlier 96.9 FM.
Now that I've created this signal we should hear the tone interfering with the radio station.
This demonstrates that if you have spurs from your device, in our case the signal generator,
it will interrupt signals of other devices operating in another channel, in this case
the 96.9 FM radio station.
Finding spurious emissions manually can be a time-consuming task that can potentially
take days to complete.
Fortunately, if you have a signal analyzer with a built-in spurious emissions measurement,
finding spurs is quick.
Now on my signal analyzer we can identify 4 spurs
and we also have a limit line for the maximum emissions according to any standard that we're trying to meet.
With this measurement table, we can also see any spurs that fail with this indicator right
here.
Identifying spurious emissions from your device will help you determine any potential design
or regulatory issues which can save you tons of time and money.
To learn more about spectrum analysis, check out the Spectrum Analysis Basics application
note in the description below, but more importantly don't forget to subscribe to our Keysight
Labs YouTube channel and follow us on our RF Facebook page!
Alright that it's for this episode thank you sooooo mu -
What the R -
Hello?
Grandma again?
Who keeps turning off the lights?
*Nick crying many tears*