Silicon Laboratories BRD4257A, Reference Manual

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7.2.1 Radiated Measurements in the 915 MHz Band
For the 915 MHz radiated power measurements, an external whip antenna (P/N: ANT-915-CW-HWR-SMA) was used as a transmitter
antenna. It was connected to the SMA connector of the BRD4257A Radio Board. The supply for the RF section (RFVDD) was 1.8 V
provided by the on-chip DCDC converter, the supply for the sub-GHz power amplifier (SUBGRF_ON, SUBGRF_OP) was 3.3 V provi-
ded by the mainboard (VBIAS through the discrete balun); for details, see the schematic of the BRD4257A. The transceiver was operat-
ed in continuous carrier transmission mode. The output power of the radio was set to 19 dBm.
The measured radiated powers are shown in the table below.
Table 7.1. Maximums of the Measured Radiated Powers in EIRP [dBm]
Frequency EIRP [dBm] Orientation Margin [dB] Limit in EIRP [dBm]
Fund 20.8 YZ/H 9.2 30
2nd -30.1 YZ/H 30.9 -20 dBc
3rd -47.6 XY/V 6.4 -41.2
4th -49.5 YZ/H 8.3 -41.2
5th
<-50
*
-/- >10 -41.2
6th -48.5 YZ/H 7.3 -41.2
7th
<-50
*
-/- >30 -20 dBc
8th
<-50
*
-/- >10 -41.2
9th
<-50
*
-/- >10 -41.2
10th
<-50
*
-/- >10 -41.2
* Signal level is below the Spectrum Analyzer noise floor.
As shown in the table, the fundamental is below the regulation limit by more than 9 dB, the harmonic levels are also compliant.
7.2.2 Radiated Measurements in the 2.4 GHz Band
For the transmitter antenna, the on-board printed inverted-F antenna of the BRD4257A Radio Board was used (the R1 resistor was
mounted). The supply for the RF section (RFVDD) was 1.8 V provided by the on-chip DCDC converter, the supply for the 2.4 GHz
power amplifier (PAVDD) was 3.3 V provided by the mainboard; for details, see the schematic of the BRD4257A. The transceiver was
operated in continuous carrier transmission mode. The output power of the radio was set to 19 dBm based on the conducted measure-
ment. During the measurement the sub-GHz antenna (P/N: ANT-915-CW-HWR-SMA) was attached to the SMA connector.
The results are shown in the table below.
Table 7.2. Maximums of the Measured Radiated Powers in EIRP [dBm]
Frequency EIRP [dBm] Orientation Margin [dB] Limit in EIRP [dBm]
Fund 21.4 YZ/H 8.6 30
2nd -46.7 XZ/H 9.1 -37.6
3rd
<-50
*
-/- >10 -37.6
4th
<-50
*
-/- >10 -30
5th
<-50
*
-/- >10 -37.6
* Signal level is below the Spectrum Analyzer noise floor.
As shown in the table, due to the high gain of the inverted-F antenna, the level of the fundamental is higher than 19 dBm. The strongest
harmonic is the double-frequency one and it is compliant with the -37.6 dBm applied limit with ~9 dB margin.
BRD4257A Reference Manual
RF Performance
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