Smart Machine Smart Decision
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
5
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.
z The input impendence of the antenna should be 50Ω, and the VSWR should be less than 2.
z It is recommended that the GSM antenna and the BT antenna should be placed as far as possible.
z 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:
