Solution #1. Verify Input/Output Configuration. The RV-M7 GX has numerous I/O options. RS232 is standard, but RS485 or RS422 may be configured also. Use the ATIO command to view how the I/O is configured. ATIO 0 is the default (RS232 mode).
Solution #2. Verify the serial port baud rate. This is difficult if it is set wrong, because you cannot enter the command mode to check it. Try all possible baud rates, and see if one of them works with the modem. Alternately, remove the rear cover of the modem, and press the CONFIG button. This will force the modem into the Command Mode, as well as set the serial port to 9600 baud, 8 data bits, one stop, and no parity. If the baud-rate was OK, verify the AT, BT and CT times, that they are long enough for you to enter the +++ string.
Solution #3 Verify the KEYPHRASE is correct. If encryption is used, the KEYPHRASE is set to a unique word, and must be the same in all radios in the system. If it is not used in the radio system, then the KEYPHRASE in all units must be disabled or left at the factory default. To disable encryption, use the KEYPHRASE 0 command. The factory default KEYPHRASE is RAVEON, in all capitol letters.
Solution #4. Verify the IDs. The TOID of the sending unit must match the MYID of the receiving unit.
Solution #5. Verify the Group. The default group code in the RV-M7 and ATLAS PL is 0. Group code 0 means the group feature is not used. Any other value for the group code will require that ALL radios in the system that must communicate, must have the same group code.