Most of the serial communication devices or data loggers are equipped with a 9-pin serial port and connected to PC using 8-wire serial cable. This method of communication though versatile is limited to short distances of no more than 150 ft. Short-haul modem (SHM) modem provides an efficient and lowcost option for increasing communication distance using 4-wire telephone cable for up to 2.2 miles (3.5 Km) at 4800 baud rate. Communication distance varies with data transfer rate. Refer to specifications table for communication distance at other data speeds. Short-haul modem is bi-directional converter for RS-232 and RS- 485 for increasing the communication distance between data logger and PC.

This method of communication uses unconditioned 4-wire telephone lines with RJ-11 connector or any 4-wire 24AWG cable connected to screw terminals. SHM is DIPswitch selectable for DCE and DTE operations, depending on whether modem is connected to PC or to serial device/ data logger. Simply, connect host modem serial port on PC and remote modem to serial port on logger, connect the two modems using a telephone wire or a 4-wire 24AWG cable, set switches SW1 and SW2, PC and modem are ready to communicate. A simple setup using SHM-115 is shown in the figure below.

Features SHM-485(N) RS-232 to RS-485 Bi-directional Converter Data transmission controlled by the RTS signal DCE/DTE selectable Point to point, multidrop, and simplex/duplex link selection Four wire full duplex/two wire half duplex Monitor configuration support Compact Size SHM-115 Non-powered Short-haul modem No external power required DCE/DTE switch selectable Analog loop back Compact size Full Duplex / Simplex Switch Selectable No external power required, Powered from RS-232 interface

Specifications SHM-485(N) SHM-115