5.2.2 FCC15.247 Emission Limits for the 902-928 MHz Band
FCC 15.247 allows conducted output power up to 1 Watt (30 dBm) in the 902-928 MHz band. For spurious emmissions the limit is
-20 dBc based on either conducted or radiated measurement, if the emission is not in a restricted band. The restricted bands are speci-
fied in FCC 15.205. In these bands the spurious emission levels must meet the levels set out in FCC 15.209. In the range form
960 MHz to the frequency of the 10th harmonic it is defined as 0.5 mV/m at 3 m distance (equals to -41.2 dBm in EIRP).
In case of operating in the 902-928 MHz band, from the first 10 harmonics only the 2nd and 7th harmonics are not in restricted bands.
The 6th is also not in a restricted band, but only if the carrier frequency is above 910 MHz. For these the -20 dBc limit should be ap-
plied. For the harmonics that are in a restricted band, the -41.2 dBm limit should be applied.
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.
FCC 15.247 regulation requires the 6 dB bandwidth of the modulated signal to be not less than 500 kHz. It also specifies the following
Spectrum Analyzer settings for measuring the unwanted emissions above 1 GHz:
• Detector: Average
• RBW: 1 MHz
Based on measurements, among the available modulation schemes, the one with the narrowest 6 dB bandwidth, that complies with the
>=500 kHz condition is the 2GFSK modulation with 500 kbps datarate and 175 KHz deviation. The following table shows the relative
levels of the measured modulated signals compared to the unmodulated levels with the specified Spectrum Analyzer settings in case of
the above modulation scheme.
Table 5.3. Measured Relaxation Factors
Frequency (915 MHz)
Modulation: 2GFSK, 500 kbps, 175 kHz [dB]
2nd harmonic
1.9
3rd harmonic
3.4
4th harmonic
4.3
5th harmonic
4.6
6th harmonic
4.9
7th harmonic
5.1
8th harmonic
5.4
9th harmonic
5.3
10th harmonic
Under noise level (0 is used)
The above values will be used as worst case relaxation factors for the 915 MHz radiated measurements.
5.4 RF Performance
5.4.1 Conducted Power Measurements
During the conducted measurements, the BRD2600A board was supplied through its USB connector by connecting to a PC through a
USB cable. The supply for the RF section (RFVDD) and the power amplifier (PAVDD) was 1.8 V provided by the on-chip DCDC con-
verter.
The RF output of the board was connected directly to a Spectrum Analyzer. The transceiver was operated in continuous carrier trans-
mission mode, the output power was set to 14 dBm.
UG508: EFR32FG23 Dev Kit User's Guide
Radio
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