EMI

The EMI I/O creates an environment that can be used for EMI pre-compliance testing. It sets up the instrument appropriately for performing the measurements and determines the frequency spectrum of the input signal, which is displayed in a graph.

The EMI I/O adds a new toolbar to the user interface of the software with all relevant settings. Additionally it gives access to four standard limit lines (EN61326-1:2006 / EN55011:2007) that can be added to the graph for easy comparison.

The EMI I/O has five output signals that can be shown in a graph:

Frequency spectrum: the defined frequency spectrum of the measured input signal
Group 1 Class A Radiated Emissions limit: Class A limit line according to EN55011:2016
Group 1 Class B Radiated Emissions limit: Class B limit line according to EN55011:2016
Group 2 Class A Radiated Emissions limit: Class A limit line according to EN55011:2016
Group 2 Class B Radiated Emissions limit: Class B limit line according to EN55011:2016

Information:

The EMI I/O can only be used in combination with the following instruments:

Handyscope HS6 DIFF - 1000XMEG
Handyscope HS6 DIFF - 1000XMESG
Handyscope HS6 DIFF - 1000XMEG-W5
Handyscope HS6 DIFF - 1000XMESG-W5
Handyscope HS6 - 1000XME
Handyscope HS6 - 1000XMES
Handyscope HS6 - 1000XME-W5
Handyscope HS6 - 1000XMES-W5
WiFiScope WS6 DIFF - 1000XMSG
WiFiScope WS6 DIFF - 1000XMESG
WiFiScope WS6 DIFF - 1000XMEG-W5
WiFiScope WS6 DIFF - 1000XMESG-W5
WiFiScope WS6 - 1000XME
WiFiScope WS6 - 1000XMES
WiFiScope WS6 - 1000XME-W5
WiFiScope WS6 - 1000XMES-W5

Only one channel of an instrument with option E can be connected to an EMI I/O.

Properties and actions

To control the behavior of the EMI I/O, several properties and actions are available. These can be accessed through a popup menu which is shown when the I/O is right clicked.

The EMI I/O also adds a new toolbar with all relevant settings to the user interface of the software.

Continuous

Enabling or disabling Continuous starts or stops continuous measuring.

One shot

Enabling One shot starts a single measurement. When the Mode is set to averaging, OneShot performs as many measurements as is set for the averaging mode and then stops again.

Mode

The EMI I/O supports three operating modes:

Mode Normal: Each new measurement replaces the previously displayed measurement.

Mode Max Hold: the values of each spectral component in consecutive measurements are compared and the maximum value for each spectral component is kept and displayed.

Mode Average: A number of consecutive measurements is averaged and the result is shown. Averaging can be done over 2, 4, 8, 16 or 32 measurements. When the Mode is set to averaging, a OneShot performs as many measurements as is set for the averaging mode and then stops again.

Clear

When the Mode is set to Max hold or averaging, the buffer can be cleared to erase previous measurements.

Input range

The buttons set the input range one step lower or higher, depending on which button is pressed. Clicking the range indicator label shows a pull down to select the required range from. Ranges to select from are:

0 .. 100 dBµV
20 .. 120 dBµV
40 .. 140 dBµV

When the Unit is changed, the input ranges change accordingly.

Unit

The EMI I/O supports several different measurement units:

dB
dBV
dBmV
dBµV
dBµV/m (at 10m)
dBm

When changing the unit, the axis of the graph changes accordingly, as well as the input ranges.

Minimum frequency

The property Minimum frequency sets the minimum frequency that is displayed in the frequency spectrum graph.

Maximum frequency

Maximum frequency sets the maximum frequency that is measured in the frequency spectrum graph. This affects the sample frequency of the instrument.

Zooming

Via the toolbar various horizontal zoom actions can be selected from:

Zoom in horizontally, 5 x (or 2 x, 10 x, 20 x, 50 x)

Zoomed in horizontally to an arbitrary value

Reset the horizontal zoom to full scale

Resolution bandwidth

Resolution bandwidth sets the width of each spectral component. This determines how small the frequency differences are that can be distinguished in the frequency spectrum. The setting also affects the number of spectral components. A lower resolution bandwidth value gives a more detailed frequency spectrum, but the update rate of the analyzer will be lower.

Window function

The Fast Fourier Transform treats the input signal as if it was a periodical signal. In other words, it assumes the signal is an infinitely long series of repetitions of the record. In practice, mostly the record does not contain an integer number of cycles of the signal. Therefore, if the end of the record is connected to the beginning, a discontinuity will arise, which results in extra frequency components in the resulting spectrum. This effect is called spectral leakage.

To minimize the effect of spectral leakage, the input record of the FFT can be multiplied with a Window. This is called windowing. Several windows can be chosen in the menu of the FFT I/O, which all basically perform the same action: they make the edges of the record smoother to make the discontinuities smaller. In most cases, the Flat top window or the Blackman-Harris window will give the best results. However, if your data contains an integer number of cycles, no discontinuities will occur and the rectangle (no windowing) window will give the best result. The following window functions are available for the FFT-block:

Rectangle
Hanning
Hamming
Bartlett
Parzen
Welch
Blackman
Blackman-Harris
Flat top

The default selected windows is Flat top.

Antenna attenuation

With the property Antenna attenuation the attenuation of the used antenna can be set. The value is used to display the correct values along the vertical axis of the frequency spectrum.

The default value is 0 dB (no attenuation).

Probe attenuation

With the property Probe attenuation the attenuation of the used probe can be set. The value is used to display the correct values along the vertical axis of the frequency spectrum.

The default value is 0 dB (no attenuation).

Limit lines

Two limit lines according to EN61326-1:2006 / EN55011:2007 can be shown in the spectrum graph:

Show/hide the Class A limit line

Show/hide the Class B limit line

ADC Spur compensation.

The ADC used in the instrument causes small spurs at specific frequencies in the spectrum. These spurs are small and far within the specifications of the instrument, but due to the high accuracy spectrum that is generated, they can be visible. By enabling the property ADC spur compensation they can be filtered out of the spectrum. This may affect actual frequency components at the same frequencies in your measured signal, which will then be displayed with a wrong magnitude.

ADC spur compensation is default enabled.