Design Note DN025
9 harmonic
C0
C2
8E
50
−52.4
−52.4
−52.6
−52.6
−52.4
−52.2
−52.5
−52.7
−30
−30
−30
−30
−52.6
−52.3
−53.5
−53.5
−53.3
−53.2
−53.6
−53.6
−41.2
−41.2
−41.2
−41.2
th
Table 3. Output Power and Conducted Harmonic Values Obtained
All values are in dBm unless stated. The values shown in red exceed the regulatory
requirements. If the recommended values and configuration are followed as specified in
Limit values shown in Table 3 are taken from the ETSI EN 300 220 regulations for 868 MHz
and FCC 15.247 for 915 MHz.
3.3.1.3.3
Overview of Harmonic Emission Regulatory Requirements
Harmonic emission will depend on ground plane geometry, encapsulation etc. Table 4 shows
the FCC- and ETSI limits. Above 1 GHz, FCC allows the radiation to be up to 20 dB above
the limits given in Table 4, if duty cycling is being used. The second harmonic would only be
an issue when qualifying under FCC part 15.249 since 15.247 only requires 20 dBc.
Harmonics
Limit
FCC
15.249
FCC
15.247
ETSI EN
300 220
2
nd
3
rd
4
th
5
th
6
th
7
th
8
th
9
th
54
dBV/m
20
dBc
−30
dBm
54
dBV/m
54
dBV/m
−30
dBm
54
dBV/m
54
dBV/m
−30
dBm
54
dBV/m
54
dBV/m
−30
dBm
54
dBV/m
20
dBc
−30
dBm
54
dBV/m
20
dBc
−30
dBm
54
dBV/m
54
dBV/m
−30
dBm
54
dBV/m
54
dBV/m
−30
dBm
Table 4. ETSI and FCC Limits for Harmonic Radiation
The programmed output power and size of the ground plane will affect the level of the
harmonics and thus determine the necessary duty cycling.
The allowed additional emission, or correction factor, is calculated based on maximum
transmission time during 100 ms. Equation 1 can be used to calculate the correction factor,
where t is equal to maximum transmission time during 100 ms. From Equation 1, it can be
calculated that a maximum transmission time of 50 ms, during 100 ms, will permit all radiation
above 1 GHz to be 6 dB above the given limits.
t
CF
½
20
log
100
ms
Equation 1. FCC Correction Factor
Even when an averaging detector is utilised, there is still a limit on emissions measured using
a peak detector function with a limit 20 dB above the average limit.
For more information and recommendations on how to comply with the different ETSI sub
bands please see Application Note 050 [3]. Application note AN001 [10] covers the
regulations in more detail for Short Range Devices (SRD) for license free transceiver
operation.
SWRA250A
Page 11 of 26
JOHANSON [ JOHANSON TECHNOLOGY INC. ]
