Transmitter parameter

AN4378

14/19

DocID025421 Rev 1

For the lowest band, the frequencies under 2400 MHz are not in the restricted bands, so the

level of the emissions must be 20 lower than the maximum in band emission. The

measurement is reported in Figure 12. The BlueNRG meets this specification by a large

margin.

Regarding the highest band, the frequencies higher than 2483.5 MHz are in the restricted

band, so the level of the emissions must be lower than -41 dBm. The measurement is

shown in Figure 13. From the graph it is possible to see that there is a zone where the

emissions are higher than the specification. This is only when the modulated signal is sent

in channel 39 of the Bluetooth Low Energy. This channel is an advertising channel: in this

case the interval between two packets can be set from a minimum of 20 ms and a maximum

of 10.24 sec. Also the maximum advertising packet length is 47 bytes, which is 376 bits: the

duration time of the longer advertising packet is 376 us. Considering the worst case of the

interval packet, 20 ms, and of the packet duration, 376 us, the duty cycle in this channel is

lower than 2%. FCC 15.35 (C) establishes that a relaxation factor must be applied for duty

cycles less than 100% as measured over a 100 ms period. The relaxation factor is 20 log

(TX on-time/100 ms) [dB], which is -20 dB for duty cycle less than or equal to 10%. So, the

BlueNRG meets the unwanted emission in the band edge specification, with a margin, even

at a higher band edge.

Figure 12. 2400 MHz band edge conducted emission measurement

AM17627v1

-60

-50

-40

-30

-20

-10

0

10

2.3950E+09

2.3960E+09

2.3970E+09

2.3980E+09

2.3990E+09

2.4000E+09

2.4010E+09

2.4020E+09

2.4030E+09

2.4040E+09

2.4050E+09

Frequency [Hz]

20 dB

20 dB