Selecting a Fiber-Optic Cable for GPIB-140 Series GPIB Extenders

Publish Date: Nov 13, 2006 | 8 Ratings | 2.88 out of 5 | Print


The GPIB-140 series of GPIB extenders use fiber-optic cable to extend the distance between two GPIB systems up to 2 km. The transmitter and receiver on the GPIB-140 series can work with a variety of fiber-optic cables. This document gives specifications on National Instruments T7 and T8 cables, which can be used as a reference if a different fiber-optic cable is desired.

Table of Contents

  1. Introduction
  2. Fiber-Optic Component Specifications
  3. Fiber-Optic Cable Assemblies
  4. References

1. Introduction

The T7 and T8 cables available from National Instruments meet the needs of most customers using GPIB-140 series GPIB extenders.  In some circumstances it is desirable to have cable properties not available with these cables.  This could include heavy duty cables for direct in-ground burial or operation in harsh conditions.

Many factors differentiate fiber-optic cables, including those listed below:

  • Operating wavelength
  • Bandwidth
  • Fiber core/cladding diameter
  • Numerical Aperture
  • Attenuation
The operating wavelength of the fiber-optic cable should closely match that of the transmitter and receiver for the link to work properly. The fiber attenuation should be calculated at the operating wavelength for a correct estimate of the total loss.

The bandwidth of the fiber is specified according to the signal frequency and the distance the signal is sent through the cable. The product of the signal frequency and traveling distance must not exceed the bandwidth-distance product of the fiber to maintain signal quality and avoid signal losses.

Core diameter gives a rough estimate of fiber performance – the smaller the core, the higher the bandwidth and the lower the loss. The four commonly used fibers have core/cladding diameters as follows:

Core (μm)
Cladding (μm)

Numerical Aperture (NA) is the “light-gathering ability” of a fiber. It is especially important to match the NA of the transmitter to the NA of the fiber so that all the light emitted by the transmitter is coupled into the fiber and propagated. Mismatches in NA are sources of loss when light is coupled from a lower NA to a higher one.

In most cases, the cable chosen should match the respective T7 or T8 fiber-optic cable in all of the above attributes.  This will ensure the highest degree of compatibility with your GPIB-140 series GPIB extender.  If a different core diameter is chosen, you should ensure that your chosen fiber-optica cable matches the NA of the transmitter, as defined in the section below.

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2. Fiber-Optic Component Specifications

GPIB-140 series extenders use fiber-optic transmitters and receivers to extend the GPIB signals.  The GPIB-140(A) provides a maximum distance of 1km, while the GPIB-140(A)/2 provides for up to a 2km extension.

Fiber-Optic Transmitter




HFBR1414 or equivalent
HFBR1312 or equivalent
Operating wavelength
820 nm
1300 nm
0.3 for 100/140 μm fiber cable
0.275 for 62.5/125 μm fiber cable
0.20 for 50/125 μm fiber cable

0.275 for 62.5/125 μm fiber cable
0.20 for 50/125 μm fiber cable
Minimum Peak Power coupled
into a 1 m fiber-optic cable
–9.5 dBm for 100/140 μm fiber cable
–15.0 dBm for 62.5/125 μm fiber cable
–18.8 dBm for 50/125 μm fiber cable
–16.0 dBm for 62.5/125 μm fiber cable
–19.5 dBm for 50/125 μm fiber cable
Connector Type

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3. Fiber-Optic Cable Assemblies

The T7 and T8 cable assemblies offered by National Instruments are for use with the GPIB-140 Series GPIB extenders.  It is possible to utilize a fiber-optic cable of your choosing if you require properties not attainable through the T7 or T8 cable assemblies.  The specifications supplied in this document will provide you with the information you need to choose an appropriate cable for use with your GPIB-140 Series GPIB extender.

T7 Cable Assembly
  • For use with GPIB-140(A) Extenders
  • Available in 10m increments to 1000 m
T8 Cable Assembly
  • For use with GPIB-140(A)/2 Extenders
  • Available in 10m increments to 2000 m


Cable Specifications

The specifications in this section apply to both T7 and T8 cable assemblies, except where otherwise noted.


Duplex, riser-rated, Ultra-Fox™ series
62.5/125 μm core/cladding diameter
Graded index
Tight buffered

Optic Fiber -- Glass
Outer Jacket -- Flame-retardant, fungus-resistant, soft, resilient PVC

International and National Standards
ISO 9001-1987
ANSI/ASQC Q91-1987
Meet NEC sections 770-51(b) and 770-53(b) for use in vertical runs

Cable diameter -- 3.0 by 6.5 mm (0.12 by 0.26 in.)
Buffer diameter -- 900 μm (0.035 in.)
Weight -- 16 kg/km (11 lb/1000 ft)

Performance Characteristics

   T7 Cable Assembly  T8 Cable Assembly

(numerical aperture)


Operating Wavelength

850 nm

1300 nm

(at Operating Wavelength)

3 dB/km

1 dB/km

(at Operating Wavelength)

160 MHz-km

500 MHz-km

UL Rating

OFNR riser-rated (can also be used as general-purpose or residential cable)

Tensile Load Rating

1000 N/220 lbf (short term, i.e. during installation)
500 N/110 lbf (long term)

Minimum Bend Radius

Under Load: ~ 5 cm
Without Load: ~ 3 cm

Crush Resistance

750 N/cm

Impact Resistance

1000 Impacts

Flex Resistance

7500 Cycles

Operating Temperature

–40° to +85° C

 Storage Temperature

 –55° to +85° C

Fiber Buffer Construction Details
Ultra-Fox™ cable features:

  • 100 kpsi proof-tested fiber
  • A primary buffer of UV-cured acrylate material to a diameter of 250 μm
  • A secondary buffer of high performance PVC to 900 μm
  • The versatile buffer system above permits mechanical stripping in short length (about 1 cm) to remove
  • The PVC secondary buffer and leave the 250 μm primary buffer intact for splicing into similar buffered
  • Fibers from loose tube cable or for Local Injection and Detection (LID) splicing techniques
  • The 250 μm buffer may further be mechanically stripped to the 125 μm glass diameter for splicing
  • Alternately, the primary and secondary composite buffer may also be stripped in one step for direct termination with connectors

ST style (Methode 908 series)

Nut -- Zinc Alloy, Nickel Plated
Body Reinforced Composite Polymer

  • Connectors mate with AT&T ST® products and all other functional equivalents, optically and mechanically.
  • One-piece nickel plated zinc body construction for easy field or factory termination in less time
  • Coupling nut with radial track to minimize mating effort
  • Accommodates tight and loose tube buffer cables with jacket outer diameters of up to 3.1 mm
  • Polymer ferrule pedestal supports fiber during polishing – no epoxy bead
  • Standard 0.155 in. hex crimp, same tool as SC and FC
  • Universal dust cap with lanyard

Performance Characteristics
Fiber Size -- 62.5/125 μm core/cladding diameter
Attenuation Loss -- <0.1 dB typical <0.5 dB maximum
Insertion Loss:
<0.3 dB typical
<0.1 dB max increase 500 cycles

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4. References

For more information, see the following documents and related links:
  • ANSI/IEEE Standard 488.1-1987, IEEE Standard Digital Interface for Programmable Instrumentation.
  • Amphenol Fiber-Optic Designer's Handbook, 1983, Allied Corporation.
  • Low-Cost Fiber-Optic Links for Digital Applications up to 155 MBd, 1993, Hewlett Packard Co.
  • Technician's Guide to Fiber-Optics, 1987, Delmar Publishers Incorporated.
  • Designer's Guide to Fiber-Optics, 1982, AMP Incorporated.

Related Links:
GPIB-140A User Manual
GPIB-140 User Manual
DevZone Tutorial: Extending the IEEE 488 Bus

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