EMI/EMC | Intro to the Spectrum Analyzer Mode | Keysight Technologies


If you are unfamiliar with the X-Series
spectrum analyzer, we are going to introduce you to some of the features of the spectrum
analyzer, particularly those that are of interest to the EMI user. Let us start by looking at CISPR presets under
the “Mode Setup” key. For EMI users, you will find a useful family
of CISPR presets, which lets you easily set the analyzer to particular CISPR bands, including
setting the number of points in the sweep to have 2 trace points for “res bandwidth”. In this case, with a “res bandwidth” of
120 kHz, we have set the point spacing in the sweep to 60 kHz, giving you 4,503 points. With the X-series, you can set up to 40,000
sweep points, allowing you to resolve very narrow signal spacings, even in a wideband
sweep. Notice that the sweep time is impacted by
changing the number of points. Now, let us talk about some of the other labor-saving
features of the X-series. First of all, you have up to 6 traces which
you can operate in any of 4 writing modes, including “trace average” and “max hold”. You can display all the traces at the same
time if you like. I can turn on an average trace at the same
time as a peak trace, and all the traces display in different colors, so it is easy to distinguish
them. We have up to 12 markers which you can use
to gain more insight into the behaviors of specific signals. You have got “peak search” functionality
that lets you easily look at different peaks in your system. You can turn on the delta marker, which allows
you to look at the differences between peaks. You can turn on marker functions, which lets
you measure power characteristics of specific signals. With a marker table, you can look at all of
your markers at the same time, including the marker functions as well as the delta markers. Again, all 12 markers can be displayed simultaneously. I can also turn on a peak table, which will
show me the top 20 peaks in my signal, which is not related to the marker functionality. I can turn all the markers off and still have
my 20 peaks displayed. These peak table peaks are real-time functions. If I change some functionality, like if I
change the peak threshold so that the number of peaks that are being displayed changes,
this all happens real-time. Peak table, marker table, traces and markers,
marker functions are some labor-saving features of the X-series analyzers. Let us go back to our CISPR preset and take
a look at some other features of the analyzer. Besides the swept mode of the analyzer, all
X-series analyzers also have FFT sweep modes, which the analyzer will automatically choose
if you get into a narrow bandwidth. For example, if we were sweeping over a narrower
span say 1 MHz and we lowered the resolution bandwidth to say 200 Hz, you can see that
it automatically switches into the FFT sweep mode, which speeds up the sweep time to 232
milliseconds as opposed to the value 40 seconds, which is what it would have been if we had
stayed in swept mode. All Agilent X-Series analyzers contain a digital
IF, which is particularly nice when you are making EMI measurements. I am going to explain that. First, I am going to preset the analyzer,
and then I am going to switch from an antenna to a signal generator. Hang on just a second. Okay, now I am back driving a signal about
-10 dBm at 1 GHz into the analyzer, and one of the labor-saving features of the X-series
is this auto-tune functionality that automatically tunes to the strongest signal in the measurement
range. The analyzer sets the span to show the whole
signal bandwidth and sets the reference level so that the signal is 10 dB below the top
of the screen. Now I can show you that it does not matter
where on the display that I place the signal, the value that you are reading does not change,
even when you put it off the top of the screen. There is no dependence on the display placement
of the signal for accuracy, which is not true when you are dealing with an analog log amp. Another advantage of the digital IF is that
you can use a single signal path to make all your measurements, even with the EMI detectors.
Whereas with analyzers that have an analog log amp you have to use a different signal
path to make normal detector measurements as opposed to EMI detector measurements. The accuracy of the X-series for EMI measurements
is unsurpassed. Of course, the X-series includes an overload
detector. Anytime the signal amplitude gets too high,
the overload detector will go on instantly telling you that you need to reduce your signal
level. This is absolutely crucial when you are making
EMI measurements. If you get an overload, it is going to invalidate
all of your readings, even at other frequencies. The overload detector is an essential part
of the digital IF. Okay. Let us go back to the antenna, and let
us go back to our band C CISPR preset. I am going to show you the limit line and
Ampcor capabilities of the X-series. You can load amplitude corrections. The analyzer supports up to 6 corrections
simultaneously, and it is easy to load them from mass storage. You just go into the mass storage system,
choose “Amplitude Correction”, and then it is easy enough to find the EMC limits and
Ampcor files that are preloaded on all of our analyzers. Let us load an amplitude correction that includes
an antenna factor. How about this bi-conical antenna here? You can see that when you turn that correction
“on”, you do get a change in the amplitude characteristics of the signal you are measuring. You can even edit the correction factor using
Agilent’s advanced correction editor. You can see that as you move through the correction
table, the little cursor follows you across the screen, and you can get to any particular
point and easily edit the amplitude of that point. I am turning the knob to show you how easy
it is to edit data in the corrections table. Besides corrections, the analyzer also includes
a set of limit lines, which are useful when you are making EMI measurements. If I go to the limit file type, again, the
analyzer includes a set of preloaded limits – or you can define your own. In this case, I am going to choose an EN55022
limit for 10 meter radiated. There is your limit line. You can see that the signal, if it crosses
the limit line, turns red, which makes it very easy for you to see when you have crossed
your limit. When you turn on a margin, you can see that
if it crosses the margin it turns amber, and it will tell you in the corner whether you
re failing your limit, failing your margin or, passing. Just as with Ampcor, you can have up to 6
limits. Each limit can apply to one of the 6 traces
or you can have multiple limits apply to the same trace. You can have up to 2,000 points in a limit
array just like you can have up to 2,000 points in an Ampcor array. That is a lot more points than were supported
on our earlier analyzers. There is a limit editor just like there is
an Ampcor editor, which lets you go into the limit array and adjust the frequency or amplitude
of any of the points in the array. You can see that it is very easy I am turning
the knob here to adjust the amplitude of this particular point in the limit array. It is very easy to adjust the values in a
limit line using the limit editor. You can insert points. You can delete points. You can customize limits pretty much any way
you like. Of course, you can save them off to mass storage
as CSV files, which makes it easy for you to edit them in Excel. You can do that with amplitude corrections
as well. Now, there is another interesting capability
in the limit editor called “Build from Trace”. I am going to go build a different limit from
Trace #1. We are going to build Limit #3 from Trace
#1. Notice Limit #3 applies by default to Trace
#2, so when I went into the limit editor and turned on Trace #2, which I had previously
saved as the noise for my measurement. If I build Limit #2 from Limit #3 from Trace
#1, now you can see the blue line there is a limit that was built from Trace #1. That makes it easy for you to build a limit
line based on the behavior of some kind of a golden device that you want to use to test
other devices with. You can see that it is reporting the limit
results for both Trace #1 and Trace #2. It will report limits for each of the 6 traces
here in the corner of the display. Then this summary area here shows you if any
of the existing limits is causing a failure to any of the traces. A lot of capability built into the limit system
and the limit editor. I am going to turn off Trace #2, and I am
going to delete Limit #3 because the display is getting a little busy here. We have talked about mass storage and how
you can save limits and Ampcor as CSV files. Well, no mass storage system would be complete
without the ability to easily do screen dumps. When you ask for a screen image on the X-series,
not only does it make it easy to generate the screen image, but it actually shows you
a thumbnail representation of the image that it is going to dump so that you can verify
that this is what you are after. You can go into the “Save As” dialogue
and save your image to internal memory. You can save it to a thumb drive. You can
save it to a network drive. It is easy as pie. And once you have saved a file type, whether
it be a screen image or a state, or a trace, the next time you push the “Quick Save”
button, it saves another file just like the one you previously saved. If you want to save screens, it is easy to
do screen dumps all day by just continuing to hit the “Quick Save” button, and it
simply increments the suffix in the file name making it really easy for you to do screen
dumps at any time. Also, as far as states are concerned, we have
6 built-in state registers. If you save to one of those, it shows you
the time when you made the save, and that makes it easy for you to see what registers
you have been using and identify what states are in what registers. Of course, it is easy to save states to files
as well, again, on a thumb drive or a network drive as well as to internal memory. There is also trace registers available when
you want to save traces. With every trace save, you get the state of
the analyzer. When you load it back in, you will get all
the settings back that you had when you saved the trace. There is a quick look the X-series spectrum
analyzer and some of the labor-saving features that it provides. Now let us go on and talk about the EMI receiver…

Leave a Reply

Your email address will not be published. Required fields are marked *