It's due reducing Noise during Communication.
In this Datasheet (https://www.arduino.cc/en/uploads/Main/Quectel_M10_datasheet.pdf)
you may find on Page 51, the Microphone Scheme.
May someone explain what is an ESD-Anti Component ?
I found out that the ESD-Anti Component, is a Diode for Electro Static Discharge Protection.
I couldn't find the same as in the Datasheet, but similar and only SMD install.
With a bit struggle I could it solder together, and it's to test.
I tested the Module, but no sound from the Microphone.
I checked the Connections (Datasheet on Page 51) (https://www.arduino.cc/en/uploads/Main/Quectel_M10_datasheet.pdf) and looks like okay. But I don't know if the ESD diodes works, perhaps I have to change it with a non-smd.
What is a Differential Layout, as in the Datasheet ?
I tested also only with an Electret Microphone, without RF-Filter Module, and it makes Noise.
Perhaps somebody have created such a Module, or have similar Problems ?
Or may someone advise, which kind of Microphone to use ?
Edit 1 - I used a bread board to replicate that module, but it has still no sound. (seems not be a differential Layout or Anti-ESD Problem ?)
Thanks a lot