SHORT HAUL MODEM (SHM-FSK)

2. Introduction

The Short Haul Modem (SHM-FSK) is a private-line modem that allows half- and full-duplex RS-232 data communications at 9600 bps over a single dedicated wire pair and across sliding contacts. The SHM-FSK operates using pure Frequency Shift Key (FSK) at high carrier frequencies (100KHz, 106.5KHz to 150KHz, 156.5KHz). These high frequencies make the SHM-FSK particularly immune to crosstalk and outside noise interference, providing highly reliable, continuous data transmission over distances

of several miles in harsh industrial environments.

The SHM-FSK converts digital signals to modulated high-frequency sine- wave carrier signals that can be transmitted much longer distances, with greater noise immunity, than square-wave digital signals. The digital Space and Mark (or 0 and 1) are converted in the transmitter to carrier signals having two slightly different frequencies that are identified by the receiver and reconverted to the digital signals. The SHM-FSKs are configured as either Master or Remote units and can be used for either point-to-point or multi- drop data communications.

The SHM-FSKs send data asynchronously. They are transparent to protocol, and to data rate from DC to 9600 baud.

The SHM-FSK can be configured as a master unit or as a slave unit. See page 13 for more information.

2.1 SHM-FSK Master Units (part number ME840A-M)

The SHM-FSK Master unit transmits at 106.5/100 KHz (Space/Mark) and receives at 156.5/150 KHz. A green pluggable two-position terminal block at the back of the unit is used for connection to the data line. There is no polarity to the data-line connection.

2.2 SHM-FSK Remote Units (part number ME840A-S)

The SHM-FSK Remote unit transmits at 156.5/150 KHz and receives at 106.5/100 KHz. It has the same data-line connector as the Master unit.

Both the Master and Remote SHM-FSKs are powered by nominal 24 volts DC, which is supplied to a black two-position plugabble terminal block (+ on the left, if you’re facing the pins) on the rear panel. The units are delivered from the factory with 120VAC to 24DC wall transformers which have a black plug attached. An external 24VDC supply can also be used to power up the MDLs. The current draw is 250mA.

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Black Box RS-485 Introduction, SHM-FSK Master Units part number ME840A-M, SHM-FSK Remote Units part number ME840A-S
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ME840A-M, ME840A-S, MD3318, MD3317, RS-485 specifications

The Black Box IC113C and IC175C are part of a series of versatile RS-485 interface converters designed to facilitate reliable data transmission over long distances. RS-485 is a standard defining the electrical characteristics of drivers and receivers for use in serial communications systems, and these specific Black Box converters exemplify the technology's adaptability and robustness.

The IC113C is an RS-485 to RS-232 converter, providing a seamless transition between these two common serial communication protocols. With a compact design, it boasts an operating temperature range of -40 to 85 degrees Celsius, making it suitable for harsh environmental conditions. Its key feature includes the ability to extend the communication distance up to 4,000 feet, which is ideal for industrial applications where devices may be far apart. Additionally, the IC113C includes built-in surge protection, ensuring that the device can withstand electrical noise and spikes, ultimately increasing the system's reliability.

On the other hand, the Black Box IC175C serves as an RS-485 to USB converter, bridging older serial devices with modern USB interfaces. This converter is critical for users wanting to connect legacy equipment to contemporary computing systems. Featuring a plug-and-play design, the IC175C is easy to install with no external power supply required, as it is powered directly through the USB connection. It also supports data rates up to 115.2 Kbps, ensuring fast and efficient data transfer.

Both models employ differential signaling, which enhances noise immunity and allows for greater transmission distances compared to single-ended communication standards. Furthermore, the converters support multiple nodes on the same bus, accommodating a network of devices without requiring complex wiring schemes.

In summary, the Black Box IC113C and IC175C offer essential features that cater to diverse industrial and commercial applications. With their robust construction, extensive operating ranges, and compatibility with various communication protocols, these converters enhance system interoperability and provide durable solutions for long-distance data communication needs. Whether connecting legacy systems or extending communication capabilities, these devices exemplify reliability and efficiency in modern data transmission technologies.
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