Relaxation With Modulated Carrier; Radiated Power Measurements - Silicon Laboratories BG22 Explorer Kit User Manual

5.3 Relaxation with Modulated Carrier

Depending on the applied modulation scheme and the Spectrum Analyzer settings specified by the relevant EMC regulations, the
measured power levels are usually lower compared to the results with unmodulated carrier. These differences have been measured
and used as relaxation factors on the results of the radiated measurement performed with unmodulated carrier. This way, the radiated
compliance with modulated transmission can be evaluated.
In this case, both the ETSI EN 300-328 and the FCC 15.247 regulations define the following Spectrum Analyzer settings for measuring
the unwanted emissions above 1 GHz:
• Detector: Average
• RBW: 1 MHz
The table below shows the relative levels of the measured modulated signals compared to the unmodulated levels with the above
Spectrum Analyzer settings in case of the supported modulation schemes.
Table 5.4. Measured Relaxation Factors for the Supported Modulation Schemes
Applied Modulation
(Packet Length:
125 Kb/s (PRBS9) [dB]
255 bytes)
2nd harmonic
3rd harmonic
4th harmonic
5th harmonic
As it can be observed, the BLE 125 Kb/s coded modulation scheme has the lowest relaxation factors. These values will be used as the
worst case relaxation factors for the radiated measurements.

5.4 Radiated Power Measurements

The output power of the EFR32BG22 was set to 6 dBm. The board was supplied through its USB connector by connecting to a PC
through a USB cable.
During the measurements, the board was rotated in three cuts. See the reference plane illustration in the figure below. The radiated
powers of the fundamental and the harmonics were measured with horizontal and vertical reference antenna polarizations.
silabs.com | Building a more connected world.
BLE Coded PHY: BLE Coded PHY:
500 Kb/s (PRBS9) [dB]
-2.7
-4.8
-5.5
-6.3
Figure 5.3. DUT Reference Planes
BLE 1M PHY: 1 Mb/s
(PRBS9) [dB]
-3.1 -3.3
-5.2 -5.2
-6.5 -6.7
-6.5 -6.7
UG509: BG22 Explorer Kit User's Guide
BLE 2M PHY: 2 Mb/s
(PRBS9) [dB]
-9.1
-10.7
-11.9
-11.4
Rev. 1.1 | 18
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