CHAPTER 3: INSTALLATION DIRECT INPUT AND OUTPUT COMMUNICATIONSB30 BUS DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 3-373The connections shown in the figure are for multiplexers configured as data communications equipment (DCE) units.3.4.7 G.703 and fiber interfaceThe following figure shows the combined G.703 plus fiberoptic interface configuration at 64 kbps. The 7E, 7F, 7G, 7Q, and75 modules are used in configurations where channel 1 is employed via the G.703 interface (possibly with a multiplexer)and channel 2 via direct fiber. AWG 24 twisted shielded pair is recommended for external G.703 connections connectingthe shield to pin 1a at one end only. For the direct fiber channel, address power budget issues properly. See previoussections for details on the G.703 and fiber interfaces.Figure 3-43: G.703 and fiber interface connection3.4.8 IEEE C37.94 interfaceThe UR-series IEEE C37.94 communication modules (module types 2G, 2H, 2I, 2J, 76, and 77) are designed to interface withIEEE C37.94 compliant digital multiplexers or an IEEE C37.94 compliant interface converter for use with direct input andoutput applications. The IEEE C37.94 standard defines a point-to-point optical link for synchronous data between amultiplexer and a teleprotection device. This data is typically 64 kbps, but the standard provides for speeds up to 64n kbps,where n = 1, 2,…, 12. The UR-series C37.94 communication modules are either 64 kbps (with n fixed at 1) for 128 kbps (withn fixed at 2). The frame is a valid International Telecommunications Union (ITU-T) recommended G.704 pattern from thestandpoint of framing and data rate. The frame is 256 bits and is repeated at a frame rate of 8000 Hz, with a resultant bitrate of 2048 kbps.The specifications for the module are as follows:• IEEE standard — C37.94 for 1 × 128 kbps optical fiber interface (for 2G and 2H modules) or C37.94 for 2 × 64 kbpsoptical fiber interface (for 76 and 77 modules)• Fiber optic cable type — 50 nm or 62.5 μm core diameter optical fiber• Fiber optic mode — multimode• Fiber optic cable length — up to 2 km• Fiber optic connector — type ST• Wavelength — 820 ±40 nm• Connection — as per all fiber optic connections, a Tx to Rx connection is requiredThe UR-series C37.94 communication module can be connected directly to any compliant digital multiplexer that supportsthe IEEE C37.94 standard. The figure shows the concept.When using a laser interface, attenuators can be necessary to ensure that you do not exceed themaximum optical input power to the receiver.
