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The default for the software is to not compensate for these losses in which case the view in the
EMxpert software and the image displayed on the spectrum analyzer should be the same. The user
has the option of turning on this compensation and adjusting the measured results to account for
these losses. If the compensation is set to ON in the setting then this results in the EMxpert software
viewer and the SA not showing the same magnitude in a spectral and spatial scan. The frequency of
the peaks should be the same in either case.
17. How long does a typical Spectral Scan take?
EMxpert EHX
: It depends on the spectrum analyzer performance; for example to scan a 4” x 4” PCB
with a span of 100 MHz and an RBW of 100 kHz with an Agilent MXA or a PXA takes a few seconds,
close to 1; and if you remove peak marking which is a separate function of Spectral Scan it is even faster.
Scanning area, span and RBW are user selectable.
18. How long does a typical Spatial Scan take?
EMxpert EHX
: Less than one second though highly dependent on the spectrum analyzer performance.
19. I am designing multiple layer boards. How can EMxpert help to diagnose EM problems?
Currently, there are no measurement techniques on the market that can exactly see what is going on
inside a multi-layer board. A chamber for example, will only deal with far-field and will not differentiate
between what is coming from the edge, the most external layer, the internal layers, and the interaction
between the layers. It is the most blind of all EMI test solutions to help design a better PCB with EMI
reduction at the source. Automated single probe, handheld probe, and EMxpert can differentiate at
least between the emission from the edge (where emissions from the internal layers will most likely
escape and emit) and from the surface of the external PCB layers.
If one uses a pre-amplifier, the scanner or probe could pick weaker signals from the internal layers
leaking through the external layers. A comparison of the spectral and spatial analysis with or without
amplification could then help point the source (frequency may help specify a component, and the
location will do as well). Using the Gerber of the inner layers as overlay could help confirm the weaker
emissions comes from a known PCB feature. The EMxpert and automated single probe could handle
that; the handheld probe will not work.
Clearly, the EMxpert and the automated single probe are the only adequate tools for multi-layer PCB
EMI measurements. However, the fact that the EMxpert is much faster and can track intermittent
events through peak hold with continuous scanning, makes it the best solution overall.
EMxpert Software
Appendix - FAQ
