Hi,
I have a new information about this issue.
Normaly, in my previous descritpion I have pointed that without TCP connection, sending a SMS works properly. Now I have removed the antenna and the modem reports CMS ERROR 513!
Maybe something around signal quality?
Here the values when modem cannot send SMS (=TCP enabled and connected):
at+creg?
+CREG: 1,1
OK
at+csq
+CSQ: 4,0
OK
now when TCP is disabled
at+creg?
+CREG: 1,1
OK
at+csq
+CSQ: 9,0
OK
Whith my understanding, it seems that the signal quality is very BAD.
But Why the signal quality decrease when an internet connexion is activer?