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4.18.1. RF_SYNC Multiplexing Function

RF_SYNC can be used in the RF Jamming Detection function. The RF_SYNC function and RF Jamming

Detection function can be switched by AT+SJDR command.

Table 41: RF_SYNC Multiplexing function

Pin name

Pin number

Mode 0(default)

Mode 1

RF_SYNC

RF Synchronization Signal

JD（RF jamming detection）

Note: About AT+SJDR, please refer to document [1].

4.19. Antenna Interface

There are three antenna ports for SIM800H&SIM800L, 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&SIM800L, 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:

Figure 49: GSM antenna matching circuit

R101，C101，C102 are the matching circuit, the value should be defined by the antenna design. Normally R101 is

0Ω, C101 and C102 are not mounted. The RF connector is used for conduction test. If the space between RF pin

and antenna is not enough, the matching circuit should be designed as in the following figure:

SIM800H&SIM800L_Hardware Design_V2.02

2015-07-27

SIM800L データシート(PDF) 52 Page - SIMCom