Start here
- How to connect a USB GSM modem pool: unboxing to first message, with the AT commands to test each channel.
- UK networks, SIMs and the law: which SIMs register (EE, Vodafone, O2; not Three) and what tariff to use.
- 64-port SMS gateway explained: how the two banks, USB ports and serial enumeration work.
- FAQ: ordering, delivery, warranty and compatibility.
Common issues
Only 32 serial ports appear
Each bank of 32 channels has its own USB-B host port. Connect both USB1 ports to the computer.
A module answers AT but will not register
Check the SIM is seated, the PIN is disabled (AT+CPIN? should return READY), signal is adequate (AT+CSQ above about 10) and the SIM is on a network with 2G. Three-based SIMs will not register in the UK.
Messages send from a terminal but not from my software
Make sure nothing else has the port open, the software is set to 115200 8N1 (or the rate you configured), and text mode (AT+CMGF=1) or PDU mode matches what the software expects.
Ports change number after a reboot (Windows)
Keep the unit on the same USB sockets. If numbering still moves, configure your SMS software to identify modems by their IMEI rather than COM number; most multi-modem servers support this.
Intermittent disconnects
Use short USB cables (under 3 m) or a powered hub; long unpowered runs are the usual cause. Check the ventilation slots are not blocked.
Contacting support
Email order@gsmmodems.co.uk or use the contact form, and include:
- your order reference;
- operating system and SMS software;
- what Device Manager or
dmesgshows when the unit is connected; - the output of
AT,AT+CPIN?,AT+CSQandAT+CREG?on an affected channel; - which SIM network you are using.
We answer by email, normally within one working day.
Faults and warranty
If a module or the unit itself develops a fault, email us first; many apparent faults are SIM or signal issues we can diagnose remotely. Genuine defects are handled under the 12-month return-to-base warranty; see returns and warranty.