RadiMation Application Note 147

How to perform a MIL-STD-461 RE101 Radiated Emission test

This application note explains how the MIL-STD-461 RE101 Radiated Emission test can be performed with RadiMation^®.

The "RE101, radiated emissions, magnetic field" test is applicable to equipment, subsystem enclosures and all interconnecting cables and is used to verify that the magnetic field emissions from the EUT and cabling do not exceed the specified requirements.

The exact requirements and test methods for the RE101 are specified in the MIL-STD-461.

Necessary equipment

The following devices are necessary to execute this test:

• Receiver
• Loop sensor (Antenna)
• LISN
• Cable

Configuration of the testsite

The configuration of the testsite is a loop sensor antenna connected with a cable to a receiver.

The configuration of the testsite should thus contain the following devices:

Device name	Tab in testsite configuration window	note
Antenna	Devices 1	Loop sensor antenna for the required frequency range
Spectrum Analyser	Devices 2	The receiver used for the test
Cable preamp -> analyser	Cables	Cable with a correction file specified for the loss

Note:

The LISN is only used to decouple the EUT and it is not needed to specify and configure this in RadiMation®

Configuration of the loop sensor antenna

The loop antenna needs to have the correction data applied, which is normally provided by the manufacturer, or a calibration institute. The correction data is expressed in dBpT/µV.

In RadiMation^® this can be configured by creating a correction file, which contains a Frequency and a Correction column. The frequencies and the correction values of the actual correction of the loop antenna can then be specified in the correction file. The values in the Correction column in the correction should be expressed in dBpT/µV.

Convert k-factor from dB(S/m) or dB/(Ohm m) to dBpT/µV

Some calibration certificates of loop antennas contain the magnetic field factor of the loop antenna as a k-factor with a dB(S/m) unit or a dB/(Ohm m) unit (which are exactly the same to each other). RadiMation^® expects that the values in the correction file are expressed in the dBpt/µV unit.

The conversion from dB(S/m) is: 'MagneticFieldFactor [dBpT/µV] = k [dB(S/m)] + 1.984'.

The conversion from dB/(Ohm m) is: 'MagneticFieldFactor [dBpT/µV] = k [dB/(Ohm m)] + 1.984'.

The value 1.984 is often simplified to be 2.0, but 1.984 is the more accurate value.

Note:

The relation between dBpT and A/m is: Magnetic Flux Density [dBpT] = Magnetic field [dBµA/m] + 1.984 In this equation, the constant 1.984 is derived by using: The magnetic flux density (B) in Tesla (T), is related to the magnetic field strength (H) in A/m, by the permeability of the medium ($\mu _{0}$) in Henry's per meter (H/m). For free space, the permeability is given as: $\mu _{0}[H/m]=4\pi \cdot 10^{-7}$ $B[T]=\mu _{0}*H[A/m]$ Converting from T to pT and from A/m to µA/m, and converting it to decibels, using the Log, the constant becomes: $240-120+20log^{10}(4\pi \cdot 10^{-7})=1.984$ (to be exact: 1.9841972804419248955749215547977) Also see: https://www.tf.uni-kiel.de/matwis/amat/elmat_en/kap_4/backbone/r4_1_1.html

An example correction file for this 'Magnetic Field factor' thus looks like:

Once this correction is stored to disk, this correction file can be selected in the loop antenna driver configuration as 'Magnetic Field Factor':

Perform the test

To perform the actual RE101 test, start a Radiated Emission Multiband test:

    Tests

       Radiated Emission

          Multiband

The complete test from 30 Hz up to 150 kHz has different settings for different frequency bands. All these different bands can be configured. The test can be configured with 3 bands, each using their applicable frequency range, measure time and bandwidth.

Band	Frequency range	RBW	Step size	Measure time receiver	Measure time FFT receiver
Band 1	30 Hz - 1 kHz	10 Hz	5 Hz	0.15 s	1 s
Band 2	1 kHz - 10 kHz	100 Hz	50 Hz	0.015 s	1 s
Band 3	10 kHz - 150 kHz	1 kHz	500 Hz	0.015 s	1 s

In the following screenshot a configuration is shown to perform the measurement on an EUT, applicable for the Navy Application.

The Location type setting for every band should be set to Magnetic Field antenna, as that determines that the measurement result will be shown as magnetic field values.

Start

The start frequency of the test. For example 30 kHz.

Stop	The stop frequency of the test. For example 100 kHz.

Reference Level

The reference level set in an analyser. This setting is not used when a receiver is used.

Attenuation

The attenuation set in the receiver.

RBW	The RBW set in the receiver. See the table with different bands for the specific values for the RE101 measurement.

Step size

The step size set in the receiver. See the table with different bands for the specific values for the RE101 measurement.

Measure time

The measure time set in the receiver. See the table with different bands for the specific values for the RE101 measurement.

Preamplifier

The preamplifier setting set in the receiver.

Traces

The type of trace set in the receiver. For MIL-STD-461 RE101 only a peak detector is used.

Test Equipment

The equipment used for the measurement.

Location type

The type of measurement that should be used. Set this to Magnetic Field antenna.

Max Height

The maximum height for the antenna tower. This configuration is depending on how many positions should be measured.

Min Height

The minimal height for the antenna tower. This configuration is depending on how many positions should be measured.

Steps

The number of height positions to measure. This configuration is depending on how many positions should be measured.

Move during measurement

If the antenna tower can move during the measurement. This is normally not used during MIL-STD-461 RE101 measurements, and can thus be unchecked.

Optimize Height

Find the optimal emission around a certain height. This is normally not used during MIL-STD-461 RE101 measurements, and can thus be unchecked.

Distance

The distance between the antenna and the EUT. This is normally 7cm for a MIL-STD-461 RE101 measurement.

Antenna Polarization

Which polarization is used, Vertical, Horizontal or Both.

Start Angle

The minimal turn table angle.

End Angle

The maximum turn table angle.

Steps

The number of angles to measure.

Turn during measurement

If the turn table can move during the measurement. This is normally not used during MIL-STD-461 RE101 measurements, and can thus be unchecked.

Optimize Angle

Find the optimal emission around a certain angle. This is normally not used during MIL-STD-461 RE101 measurements, and can thus be unchecked.

EUT Angle Offset

The offset of the EUT on the table. This is normally not used during MIL-STD-461 RE101 measurements, and can thus be set to 0 degrees.

Limit Lines

The applicable limit line can be added, in this example the "MIL-STD-461 RE101-2 Navy Applications" limit line file.

All peaks above x dB below the limit line

Which level above x dB below the limit line the peaks should be detected.

Peak detection

How many peaks should be detected automatically, for example, use 10 peaks to be detected

Final peak measurement

It is possible to perform a final measurement on a peak with the selected detectors. Normally no final measurement is needed for the MIl-STD-461 RE101 measurement, and all detectors can thus be unselected.

When all parameters are configured for the RE101 test, press Start Test to perform the actual emission measurement.

Review the initial scan and measure frequencies for maximum emission

With the the frequencies of maximum emission located, RadiMation^® will detect any peaks above the limit line, but it is also possible to add additional peaks by clicking in the graph. A list of peaks with frequencies should appear below in the Peaks tab. As described in section 5.17.3.4c(4) and 5.17.3.4c(5) it is needed to find the maximum radiation, the following steps describe how to perform this within RadiMation.

To measure one single frequency and find the maximum radiation:

1. Select one frequency by checking one single frequency in the peaks list.
2. Click Peak Actions and select Set receiver to Peak settings to set the correct measure time and RBW as configured.
3. Enable Continuous Measure and move the loop antenna to find the maximum radiation.
4. Click Continuous Measure again to stop the measurement.
5. Repeat this step for each frequency.

Conclusion

The MIL-STD-461 RE101 test is using different receiver settings depending on the frequency band to cover the measurement of the magnetic field for the complete frequency range. All these settings can be easily configured in a multiband "Test Setup File" and tested with RadiMation^®. Also the optimization of the maximum emission can be performed, and all this information will be present in the peak table in the test results.

Equipment Under Test

Line Impedance Stabilisation Network

Decibel

Resolution BandWidth