Default Gsm keeps disconnecting

Hello all, my question is all in the title.
Almost every minute my phone disconnects from gsm for no reason and randomly.
Any help please?
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The living
Phone: Sprint lg Optimus G
Kernel version: 3.40
Baseband version: BLS970ZVB
Build number: CM_ls970-userdebug 4.3


Tablet: Galaxy tab 2 7.0
Kernel version: 3.0.31-Cm
Baseband version: Unknown
Build number: pac_p3110