Model 2870

IBM SNA Coax to Fiber Optic Modem

S.I. Tech Model 2870 Coax to Fiber Optic Modem

S.I. Tech Model 2870

The S.I.Tech 2870 Bit-Driver is designed to work with 93 ohm coaxial cable (RG 62/U type) used by IBM in SNA environment. It is a ideally suited to replace coaxial cable between IBM 3274 and 3276 controllers and 3278 terminals. It can also be used between IBM 3299 multiplexer and remote multiplexer. The normal operating data rate is 2.35 Mbps.

This fiber optic Bit-Driver product eliminates many disadvantages of coax, especially EMI/RFI, high attenuation (high signal loss), limiting distance between workstations (2000 feet coax), ground loops (electrical isolation with fiber), weight, and potential lightning damage outdoors between buildings.

S.I.Tech Model 2870 is a standalone product allowing easy change from coax to fiber: Simply disconnect the BNC connector and plug into the input/output port.

Note: SNA is IBM System Network Architecture.


Operating Mode: Synchronous, simplex or full duplex, 2.35 Mbps
Input/Output Interface: 93 ohm coaxial cable BNC bulkhead jack
Transmission Line Interface: 2 ST connector fiber optic receptacles (SMA option)
Transmission Distance: 6600 ft. (2.0 Km) (5 Km option)
Transmitter Output Power: 30 microwatts into 50 micron fiber
System Wavelength: 820 nanometers (1300 nm option)
Receiver Sensitivity: 3 microwatts at less than 10-9 bit error rate
Operating Temperature: 0°C to 50°C
Metal Enclosure: 7.5" x 7" x 3"
(19 x 17.8 x 7.6 cm)
Weight: 3 lbs. (1.36Kg)
Input Power: 110 VAC 50/60 Hz
230V Version: 2870V
Rack Mount Version: 2370 (3000 rack)

RS-485 DB-9M Male Connector Pins Utilized by Model 2870

Pin No. Description
1 Ground
3 Data -
5 Ground
9 Data +

Operating Distance for Fiber Optic Cable

S.I. Tech Model 2870 Diagram

Optical unit connection: Connect the optical transmission line to the
T and R receptacles. Note which cable channel goes to T or R by noting cable imprint. On the other end, reverse the connection.

Note: Some fiber types in short distance applications may overload the receiver. If other than coax cable is used, use balun (impedance matching transformer)

S.I. Tech Model 2870 Diagram

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