M66 GSM Module Antenna is short with ground

Technical Subjects Hardware RF/Antenna
1

Hi,
I am working with M66FB-03-STD module by creating a compatible PCB in my lab. It was working well. Then I put this module at an industry where huge EMI was observed. Here the module was not able to synchronize with network. I changed different SIM cards and found no solution. Then after a detailed check up, I found that the GSM Antenna pin in the module was short with ground.
Luckily I was having another PCB with M66FA-04-STD with me, which I checked for the same short circuit. But this module was not having the short circuit and it also worked well in that industry.
So please let me know what could be the reason for that short circuit between Antenna pin and ground in M66FB-03-STD. If it is a problem, what is the solution, since I have nearly 20 modules with me having the same issue.

2

Hi Anoop ,

please check if it is complete short or there is some small resistance there .

If some small resistance there then there should not be any problem .

This shorting may be due to the filter component being used , in case of inductor based filter you see shoring and in case of capacitor based filter you see high impedance .

This should be fine , for non connection to network you please check your antenna design and also check if sim cards are being detected .

3

Hi Ratan,

Thank you for the reply.

The resistance I am getting between Antenna pin and ground is 1.6 ohms for M66FB-03-STD.

For M66FA-04-STD, its completely open circuit.

The module was not getting synchronized with network, even after the SIM card being detected.

Regarding Antenna design; I will check my design. Also can you sent a sample Antenna PCB design for M66FB-03-STD.

4

Same problem here. I have been using the M66FA-04-STD for tests and everything worked fine. Now I have chage it by the M66FB-03-STD and can’t attach to the network.
I have done the same, I checked the antenna pin and found that it was short with ground. As Ratan say, it may be normal.
Could you send me some AT command that allow me to check if everything is ok with the module?

5

Hi ,

you can check

AT+CPIN?
AT+CSQ // any thing other than 99 seems to be ok , if it is 0 to 10 then signal is low
AT+COPS=? if you get operators means RF is able to scan .

6

Thank you.
I just needed to wait longer for the new modems. First attach, for whatever reason, is slower.
The shortcircuit to gnd is normal for this module versión.