DocID025421 Rev 1

11/19

AN4378

Transmitter parameter

19

Figure 8. Unwanted emission in non-restricted band from 2.5 GHz to 26 GHz measurement

3.4.2

Unwanted emission in restricted frequency bands

According to FCC part 15.247 all the emissions which fall in the restricted bands, as defined

in part 15.205, must comply with the radiated emission limits specified in part 15.209.

Since the emission limits provided in 15.209 are specified in terms of radiated field strength

levels, measurements performed to demonstrate compliance have traditionally relied on

radiated levels, however conducted measurements performed at the antenna connector are

acceptable to demonstrate compliance.

Additionally, when a conducted test is performed in lieu of a radiated test, an additional

factor must be added to the measured value to account for possible ground reflections. For

emissions at frequencies less than or equal to 30 MHz, a ground reflection value of 6 dB

shall be used. For emissions at frequencies greater than 30 MHz but less than or equal to

1000 MHz, a ground reflection value of 4.7 dB shall be used. For emission on frequencies

greater than 1000 MHz, no ground reflection factor is applied.

Also, when a conducted power measurement is performed in lieu of a radiated test, the gain

of the transmitting antenna must be added to the measured output power. In this application

note the data are shown without taking into account the antenna gain. It is recommended

that all users of the BlueNRG device take into account the antenna gain in accordance with

the “Guidance for Performing Compliance Measurements on Digital Transmission Systems

(DTS) Operating Under Part 15.247” [3] document, paragraph 10.2.2.2.

Regarding the measurement detectors, part 15.35 specifies that for frequency below 1000

MHz, the radiated emission limits assume the use of a CISPR quasi-peak detector function

and related measurements bandwidth. As an alternative, compliance can be demonstrated

for the applicable emission limits using a peak detector. For frequencies above 1000 MHz,

the radiated emissions levels assume the use of an average detector and a minimum RBW

of 1 MHz. In addition, when average radiated emissions measurements are specified, there

is also a limit on the peak emissions level which is 20 dB above the applicable maximum

permitted average emission limit.

AM17623v1

-60

-55

-50

-45

-40

-35

-30

-25

-20

-15

-10

2.5000E+09

7.5000E+09

1.2500E+10

1.7500E+10

2.2500E+10

Frequency [Hz]