Model 373/374/376

10BaseT to Fiber Optic
Full-Duplex Converter

Reference Manual

0315-0269 Rev. C


Printed 12.18.01

Table of Contents

1.0 Introduction
1.1 Features
1.2 The Model 373/374/376 vs. the Two-Port Repeater

2.0 Installation
2.1 Location
2.2 Connections

3.0 Operation
3.1 Status LEDs
3.2 Link Integrity Test Switch Enable/Disable
3.3 Starting Up the Model 373/374/376
3.4 Diagnostic Checks

4.0 Device Specifications
5.0 Help


1.0 Introduction

The Model 373/374/376 10BaseT to Fiber Optic Full-Duplex Converter offers an inexpensive means to break the distance barrier of 10BASE-T compliant LANs while utilizing network connections that are safe from electrical interference. The Model 373 performs the translation of signals between a 10BASE-T compliant link and a 10BASE-FL compliant link, allowing conversion from a twisted-pair segment to a multimode fiber optic segment. The Model 374 performs much like the Model 373 but has been designed to work on single-mode fiber at 1310 nm. This enables users with 10BASE-T terminal equipment to connect via fiber optic link segments that can be extended to a distance of 14 km, or 46,000 ft. Thus a LAN can be extended to distant buildings without the usual concern for electrical interference from other equipment, ground loops, power surges, or lightning strikes. If the connection from a server to a workstation is a fiber optic segment, the unit renders the connection impervious to these disturbances. The Model 376 performs the same as the Model 374 (on single-mode fiber) but at 1550 nm, which can extend the distance to 38 km.

Because the unit is a twisted-pair-to-fiber media translator, it will allow any network device with 10BASE-T compliant ports (e.g., DTEs, repeaters, fan-out units and hubs) to be connected by fiber optic cable. The Model 373/374/376 converts between electrical signals and optical signals, while ensuring that collision information is preserved and translated from one segment to the other. The operation of the device is transparent to the network. Because each port is compliant with its respective section of the IEEE 802.3 specification, full-length segment connections are allowed on both sides of the device.

Five LEDs are used to monitor the status of the device and the connected segments. In addition, a switch is provided which enables or disables a twisted-pair link integrity test.


1.1 Features

Translates signal activity between twisted-pair and fiber, including collision information 
Five diagnostic LEDs provide information regarding device operation and network status 
Compatible with IEEE 802.3 specifications for 10BASE-T and 10BASE-FL 
Supports full-length network segments on both ports 
Switch-controllable twisted-pair link integrity test 
Automatic polarity correction on twisted-pair link 
Easy to install and operate

1.2 The Model 373/374/376 vs. the Two-Port Repeater

A two-port repeater enables a user to extend the distance of a network. Degenerative effects such as jitter, cable attenuation, and media distortion limit the distance of a link segment. To transmit data across distances longer than a maximum segment length, a repeater is needed to resynchronize and regenerate the data which removes the cumulative degenerative effects.

A two-port repeater also enables a user to translate information from one type of media to another. Selection of the appropriate MAUs for the repeater set enables translation from any type of IEEE 802.3 compatible link segment to any other. Data and collision information are preserved and translated across the repeater. However, if a user simply wants to perform a media translation but does not care about extending the distance of the network, a repeater may not be necessary. By removing the signal retiming, preamble regeneration, fragment extension, and auto-partitioning functions of a repeater, the Model 373/374/376 is able to provide a cost-effective method of translating from one type of media to another.

This does not mean that the user can not take advantage of the additional network distance offered by repeaters. Because the two ports on the unit are compatible with their associated specifications, the user can connect full-length segments to both sides of the Model 373/374/376, but should do so knowing that the effects of jitter will not be eliminated by signal resynchronization. Further, adding the translator and another segment will add to the total round-trip delay for the network.


2.0 Installation

2.1 Location

The Model 373/374/376 should be located close enough to an AC power source to permit the use of the power module (supplied). In addition, it should be placed in an area that is well ventilated and away from electrically noisy equipment. Unshielded twisted-pair connection should be routed such that the effects of interference from other power or data connections are minimized.

2.2 Connections

2.2.1 Power

The power module supplied with the Model 373/374/376 provides 12 V DC (at 500-mA maximum) to the device through the power connector located next to the RJ-45 connector. The module plugs into a standard 115-V, 60-Hz AC power source. An optional 220-V, 50-Hz power module is available.

There is no ON/OFF switch on the device. When the power is connected to the device, the device is ON. This will be indicated by an illuminated power LED.

2.2.2 Fiber Optic Segment

The Model 373/374/376 provides two ST-Type connectors to interface to the fiber optic link. Power should be connected before attaching the fiber optic cables. The fiber optic cables must be terminated with ST-type connectors in order to interface with this device. It is important when dealing with fiber optic cables to verify that the TX on one end of the link is connected to the RX at the other end of the link. Some duplex fiber optic cables are coded to help monitor the direction of data travel. If the fibers are not coded, special attention must be paid to ensure a proper connection.

The maximum length of a fiber optic segment is 2 km (6,600 ft) for the Model 373, 14 km (46,000 ft) for the Model 374 and 38 km (125,000 ft) for the Model 376.

2.2.3 Twisted-Pair Segment

The Model 373/374/376 includes an RJ-45 connector to interface to a twisted-pair link. It is important to note that The Model 373/374/376 does not have an internal crossover. This means that on the Model 373/374/376, Pins 1 and 2 are outputs and Pins 3 and 6 are inputs. Thus, if connecting to a DTE, a crossover cable will probably be necessary. However, if connecting to a hub, a straight-through cable will probably be required, as most hubs have an internal crossover. The user should check the cable specifications for the device attached to the other end of the twisted-pair link to ensure proper operation. Note: The maximum length of a twisted-pair segment is 100 m (330 ft).

3.0 Operation

3.1 Status LEDs

Power: This LED illuminates to indicate that external power is connected and that the internal power converter is functioning properly and supplying power to the internal circuitry.

Fiber Link Monitor: This LED is illuminated when the input power at the RX port exceeds the minimum level. There are transitions that indicate either an idle signal or active data. If the power falls below the minimum (or transitions cease) the LED will go off indicating that there is no valid link to the RX fiber port.

Twisted-Pair Link Monitor: When link integrity testing is enabled, this LED is illuminated when the Model 373/374/376 is receiving proper link pulses from the device attached to the other end of the twisted-pair segment. This indicates the link is connected and operational. When link integrity testing is disabled, this LED is always lit when the power is on.

Traffic - This LED is illuminated to indicate that data is present at the transmit and receive port of either segment. This indicator is extended with an internal timer for visibility.

3.2 Link Integrity Test Switch Enable/Disable

The Link Integrity Test switch enables the user to enable or disable the twisted-pair link integrity test. When the test is enabled (ON), the unit will transmit link pulses over the twisted-pair segment to the attached network device when transmit data is idle. In addition, when the test is enabled, the unit will ensure that link pulses are being received from the attached network device when Receive Data is idle. If proper pulses are not being received, the unit goes into a link-fail state and ceases operation. During the link-fail state, the Twisted-Pair Link Monitor LED is OFF. The Link Integrity Test switch enables the unit to ensure that the twisted-pair link is functional.

When link integrity testing is disabled (OFF), the unit will not transmit link pulses, nor will it monitor incoming link pulses. The Twisted-Pair Link Monitor LED will always be lit.

Note: Not all network devices support link integrity testing. Check the attached network device to determine if link testing is supported. If the attached network device supports link integrity testing, the Link Integrity Test Switch must be enabled (ON) on the Model 373/374/376 to prevent the network device from interpreting the absence of link pulses as a link failure. Devices compatible with the 10BASE-T standard support link integrity testing.

3.3 Starting Up the Model 373/374/376

Plug the power adapter into the wall outlet and attach the power connector to turn the device on. Connect the twisted-pair cable and fiber optic cables as described earlier. Set the Link Integrity Test switch to the desired setting. Check the status LEDs for proper device operation.

When the device is operating, input signals to the twisted-pair port are detected, translated into signals compatible with a 10BASE-FL fiber optic link and outputted to the TX fiber optic port. Signals inputted to the RX fiber optic port are detected, translated into signals compatible with a 10BASE-T link and output to the twisted-pair port.

3.4 Diagnostic Checks

3.4.1 Power Connection

When the power connector is inserted into the receptacle in the Model 373/374/376, the Power LED should be lit. If it is not, check to see that the power module is supplying 12 V DC at 500-mA minimum.

3.4.2 Fiber Connection

When the fiber optic link is connected properly, the Fiber Link Monitor LED should be lit. If it is not, check to see that RX on one end of the link is connected to TX on the other end, and vice versa. Verify that the remote unit is powered. If the link is still not operational, check the continuity of the fiber and make sure that the fiber connectors are clean.

3.4.3 Twisted-Pair Connection

When the twisted-pair link is connected properly, the Twisted-Pair Link Monitor LED should be illuminated. If it is not, check to see that the twisted-pair cable is such that the transmit Pins 1 and 2 from the Model 373/374/376 are connected to the receive circuitry on the remote device and the receive Pins 3 and 6 are connected to the transmit circuitry on the remote device. In other words, check the specifications of the remote device to determine if a crossover cable is necessary. Verify that the remote unit is turned on. If the remote device does not support link integrity testing, make sure that the Link Integrity Test switch is set to the OFF position on the Model 373/374/376.


4.0 Device Specifications

Power Requirements

Max Input Power: 12 V at 500 mA

Power Supply Module

Input: 120 V AC, 60 Hz (220 V AC, 50 Hz optional)

Output: 12 V DC at 500 mA

Twisted-Pair Interface

Connector: RJ-45 eight-pin jack

Input Impedance: 100 ohms

Output Level: 2.3 V - 2.7 V

Min. Input Level: 525 mV

Max Link Length: 100 m

Compatibility: IEEE 802.3 Specification for l0BASE-T

Fiber Optic Interface

Connectors: Two ST-style fiber optic connectors (AMP 2.5 mm bayonet connector or similar)

Max Link Length: 2 km

Fiber Type: multimode 50/125,62.5/125, or 100/140 micron

Peak Transmit Power:

50/125 um -19.8 dBm minimum

62.5/125 um -16.0 dBm minimum

100/140 um -10.5 dBm minimum (measured out of 1 m of cable)

Opt. Power Budget:

50/125 um 12.7 dBm

62.5/125 um 16.5 dBm

100/140 um 22.0 dBm


Fiber Optic Link Monitor: Green

Twisted-Pair Link Monitor: Green

Traffic: Yellow (Internal timer extends event for better visibility)

Power: Red


1.5" W x 4.25" L x 1" H


16 oz (including power supply)


Temperature: C to 50° C

Relative humidity: 0% to 95%, non-condensing

Model 374/376

Max Link Length: 14 km/38 km

Fiber Type: single mode 9/125 micron

Peak Transmit Power:

9/125 um -27 dBm minimum (measured out of 1 m of cable)

Opt. Power Budget:

9/125 um 9 dBm

Min. Receive Power: -32.5 dBm average (for BER < 10)

Compatibility: IEEE 802.3 specification for 10BASE-FL

5.0 Help

If you require assistance, please visit our Technical Support Center.


TELEBYTE warrants the equipment to be free from defects in material and workmanship, under normal and proper use and in its unmodified condition, for 12 months, starting on the date it is delivered for use. TELEBYTE's sole obligation under this warranty shall be to furnish parts and labor for the repair or replacement of products found by TELEBYTE to be defective in material or workmanship during the warranty period. Warranty repairs will be performed at the point of manufacture. Equipment approved for return for warranty service shall be returned F.O.B. TELEBYTE factory and will be redelivered by TELEBYTE freight prepaid, except for non-continental U.S.A. locations. Non-continental deliveries will be sent COD freight plus import/export charges.

The above warranty is in lieu of all other warranties, expressed or implied, statutory or otherwise, including any implied warranty of merchantability or fitness for a particular purpose. TELEBYTE shall not be liable for any damages sustained by reseller or any other party arising from or relating to any equipment failure, including, but not limited to consequential damages nor shall TELEBYTE have any liability for delays in replacement or repair of equipment.

Out of warranty equipment may be returned to the Greenlawn, NY customer service facility prepaid as described above. Return shipping charges will be billed to the customer. The repaired unit will have a 90-day warranty. In those cases where "NO TROUBLE" is found, a reduced charge will be billed to cover handling, testing and packaging.

Whether in or out of warranty, a Return Material Authorization (RMA) number is necessary and can be obtained by visiting our Technical Support Center. Reference the RMA number on the outside container.

Document No. 0315-0269/Rev. C

Model Product Info
373 Product Page  Application Note  Specifications
374 Product Page  Application Note  Specifications

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