Smart Machine Smart Decision
SIM800H _Hardware Design_V2.03
47
2016-10-10
The timing of the synchronization signal is shown below. High level of the RF_SYNC pin indicates increased
power consumption during transmission.
Transmit burst
RF_SYNC
577us
220us
Figure 45: RF_SYNC signal during transmit burst
4.19.
Antenna Interface
There are three antenna ports for SIM800H, GSM antenna port named GSM_ANT, Bluetooth antenna port
named BT_ANT and FM antenna port named FM_ANTP/FM_ANTN, The RF interface of the three antenna
ports has an impedance of 50Ω.
The input impendence of the antenna should be 50Ω, and the VSWR should be less than 2.
It is recommended that the GSM antenna and the BT antenna should be placed as far as possible.
The isolations of the three antenna should be bigger than 30dB
NOTE
：
About the RF trace layout please refer to“AN_SMT Module_RF_Reference Design_Guide”.
4.19.1.
GSM Antenna Interface
There is a GSM antenna pad named GSM_ANT for SIM800H, the connection of the antenna must be decoupled
from DC voltage. This is necessary because the antenna connector is DC coupled to ground via an inductor for
ESD protection.
The external antenna must be matched properly to achieve best performance, so the matching circuit is necessary,
the connection is recommended as following:
GND
(Pin41)
R101
GSM_ANT
C101
C102
GND
(Pin39)
GSM
Antenna
Module
RF connector
D101
Figure 46: GSM antenna matching circuit
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