There is TVS inside module which is only to prevent ESD. If the device is required to endure thunder stroke , you can connect a professional anti-lightning TVS to the RF_IN pin outside of module and make sure that the capacitance of TVS should be lower than 0.5pF.
1. If the antennas of modules are too close to each other, it will bring EMI interference within the antennas, which will result in the decline in the signal quality and the raise of BER, and cause long time connection or connection failure issue. It is suggested that the distance between each antenna should be more than 20cm.
2. If many modules are working simultaneously, it could cause some modules unable to register to network due to lack of base station resources. It is recommended to use QuecScan/QuecLock function to lock different modules at different frequencies. For Details, you can refer to <GSM_QuecCell_AT_Commands_Manual>. Also, you can use SIM cards of different operators if possible.
The uplink and downlink time slots will be 4 in GPRS CLASS 12. Using CS4 coding method it is possible to achieve a user speed of maximum 85.6Kbps. (For Details, please refer to below chart.)
Note: The actual speed depends on the network status. For example, the actual average speed tested in Shanghai is 30kbps.
Module can drive a maximum 8ohm load resistance if there is an embedded AB amplifier inside it. If there is no embedded AB amplifier in the module, then module can drive a maximum 32ohm load resistance. It is needed to add an external audio amplifier to drive 8ohm load resistance.
1. Check if MCU sends ATH command to close the call.
2. Check whether there are capacitors with high capacitance like more than 1uF in the audio interface. In general，only 10pf and 33pf capacitor can be connected to the audio interface to eliminate the RF interference. Capacitor with high capacitance will cause the instability of audio PA, which may lead to the call hanged off.
There are two modes for SMS, Text mode and PDU mode.
1. When using text mode, it is needed to configure some parameters via AT commands like AT+CMGF, AT+CSCS and AT+CSMP.
2. When using PDU mode, you need to include all of the parameters like MS center number, receiver’s number and the validity into one PDU string.
According to the 3GPP standard, the maximum individual short message size is 1120bits. When using different coding scheme, the maximum individual short message size could be different. Please see details as below:
1. Using GSM 7-bit alphabet, the maximum individual short message size can reach to 160 characters (1120bits/7 bit=160).
2. Using GSM 8-bit alphabet, the maximum individual short message size can reach to 140 characters (1120bits/8 bit=140).
3. Using UCS2 16-bit alphabet, the maximum individual short message size can reach to 70 characters (1120bits/16 bit=70).
Long message is composed of multiple SMS messages. The long message will be split into multiple short messages and sent out. The receiving terminal is then responsible for reassembling the short messages and presenting them to the user as one long message. Each short message will start with aTP-UDH1 containing segmentation information (TP-UDH1 is set as 1). For Quectel modules, long message can contain maximum 7 short messages.
When SMS memory space is full, the incoming message cannot be received.
After executing AT+QEXTUNSOL="SM", 1, module will respond +TSMSINFO:322 when SMS memory space is full.
Module will respond error when sending some SMS commands if SIM card initialization is not finished, so it is necessary to finish the SIM card initialization before operating SMS commands. In general, SIM card initialization will be finished in about 20s after powering on. However, for some SIM cards, it will take about 40s to finish the initialization due to different electrical characteristics. You can use AT+QINISTAT to check the status of SMS initialization. +QINISTAT:3 means the SMS initialization is finished and then you can operate the SMS commands.
Note: Before SIM card initialization is finished, executing the following commands will respond error.
QMGDA /CGSMS /CSMS/ CMGL / CSAS/CRES/ CMSS /CSCB/ CMGW /CMGD/ CMGR /CPMS