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What is a LEMO fiber optic connector (also called SMPTE 304M connector)?

Table of Contents




:: Who is LEMO?

LEMO is both the name of an electronic and fibre optic connector manufacturer, based in Écublens, Switzerland, and the name commonly used to refer to push-pull connectors made by that company.

LEMO connectors are used in medical, industrial, audio/visual, telecommunications, military, scientific research and measurement applications. The company, founded in 1946, started as a manufacturer of contacts in noble and rare metals. The company took its name from the company founder, engineer Léon Mouttet.

LEMO has set several connector standards which includes the 3K.93C connector.

:: LEMO's 3K.93C connector

LEMO developed the 3K.93C Series connectors in the early stages of the introduction of HDTV, becoming the standard for high-definition TV.

When uncompressed high-definition cameras arrived in the broadcast facility, it was soon realized that copper cables could not carry these HD signals as far as their triax and coax predecessors. Even the largest coax can only go 1,000 feet or so when carrying HD-SDI video and many sports venues and similar large facilities need longer distances.

SMPTE 311M hybrid cable is the solution that filled that requirement. Designed for high-definition (HD) cameras, these composite cables can multiplex audio signals and video signals and deliver power. It includes 2 single mode fibers, 2 to 8 copper power cables, 2 low voltage control signal wires.

LEMO's 3K.93C connector has been adopted by the American (standardized as SMPTE 304M), Japanese (standardized as ARIB BTAS-1005B) and European (standardized as EBU R100-1999) standards organisations for HDTV fiber links for the broadcast market.

It is one of the only hybrid fibre connectors being used worldwide that complies fully with SMPTE 304 / SMPTE 311, ARIB and EBU standards for both signal and cable. LEMO’s 3K.93C connectors are the standard in national and international broadcast companies.


:: SMPTE 304M Connector

So in the USA, the SMPTE 304M connector is the standardized version of LEMO's 3K.93C connector.

Basically, SMPTE 304M connector is a hybrid connector that includes both fiber, power, and low voltage control signal all in one.


These hybrid connectors are designed for high definition broadcast television cameras used worldwide for the production and transmission of high definition TV programming.

Amphenol's 110 series connectors(SMPTE 304M compliant) feature two fiber optic termini and four electrical contacts. The high precision fiber termini provide single mode performance, while the two auxiliary electrical contacts permit supply of power remotely to the camera at long distances from the studio, control van or CCU. Two additional low voltage electrical contacts are provided for communication purposes. The connectors are designed for use in conjunction with SMPTE 311M Standard cables.

The connectors are fabricated from stainless steel to withstand corrosive elements when exposed to the extreme harsh outdoor environments and are sealed to an IP68 rating to block out ingress of damaging dirt, dust and moisture. The robust shells are also designed with thick walls to prevent damage from rough handling during outdoor deployment at venues such as professional sports arenas. Metal or rubber dust caps are available to protect against contamination of the interfaces. The connectors are designed for easy termination in the field.

This picture below shows the internal components of a typical SMPTE 304M connector.


:: F2 Fiber Optic Contacts:

The pre-terminated contact provides the user with a contact that can be terminated without the use of epoxy, or polishing. The F2 pre-terminated fibre optic contact is designed as a repair solution but may also be used for indoor fixed installations.

It is intended for use in situations where it is critical that a cable be repaired quickly. The pre-terminated contacts enable simple and rapid on-site-terminations for SMPTE-311M cables.

The design eliminates the need of polishing fibre-optic elements as well as preparing and using special epoxies for the fibre assembly.

The F2 pre-terminated contact is entirely compatible with, and is designed for use with, the LEMO 3K.93C Series. It also fits into any connector where the standard LEMO F2 contact is used.

LEMO now offers 3 choices of F2 ferrule size to fit your fiber dimensions. Fibers are manufactured to about 125 microns, but in some occasion the fibers might be larger.

LEMO's choice of inner ferrule diameter are fit for 125 micron, 125.5 micron and 126 micron. Designed for use with LEMO 3K.93C, these contacts can be used directly into any LEMO connector where the F2 contact is used.


:: How to mate SMPTE 304M connectors?

SMPTE 304M connectors have a push-pull self-latching connection mechanism. The connector can be mated by simply pushing the plug axially into the socket as shown below.

This video below shows how to mate and unmate SMPTE 304M connectors.



There are dozens of shell designs for the mating of SMPTE 304M connectors in different situations.

Here are a list of the shells, plugs, free sockets, fixed sockets, and more with their respective application situations.


:: How to clean SMPTE 304M Connectors?

You need to extract the alignment sleeve before cleaning the ferrules inside the SMPTE 304M connectors.

This can be done with the LEMO alignment tool which is double ended with threads on both ends.

You can use this tool to install/extract the F2 contact alignment devices (the mating sleeves basically).

This video shows the whole process.



:: What is SMPTE 311M Cable

On the other hand, you need the SMPTE 311M standard compliant cable to work together with SMPTE 304M connectors.

SMPTE 311M hybrid cable is the solution that filled that requirement. Designed for high-definition (HD) cameras, these composite cables can multiplex audio signals and video signals and deliver power. It includes 2 single mode fibers, 2 to 8 copper power cables, 2 low voltage control signal wires.

Here is a cross section of a typical SMPTE 311M hybrid cable.

SMPTE 311M Cable Composition

SMPTE 311 cable is composed of:

  • 2 Single-mode fibers:
    • 9.5 µm/125 µm
    • Wavelength 1250-1625 nm.
    • ≤ 0.8 dB/Km
  • 2, 4 or 8 Power conductors (Auxiliary Conductors according to standard):
    • Voltage: 600 Vac
    • Current: 10 A
    • Section: 0.6 mm2
  • 2 Low Voltage conductors (control or signal) (Signal Conductors according to standard):
    • Voltage: de 42 Vac a 60 Vac
    • Current: 1 A
    • Section: 0.22 mm2

What signals are transmitted?

This hybrid cable transmits video, audio and control (signal between the camera and its CCU) delivering power signal also.

What are the benefits?

The main advantage is that it allows higher lengths compare to triaxial cable or coaxial cable without increasing weight and flexibility. The central strength member gives the needed durability for a continuous use.

Where is it used?

This connectivity solution is suitable for transmission in arenas, stadiums or sport events and big installations where long cable runs is required.

Professional cameras examples using SMPTE 304/311:

Alexa Fiber Remote, JVC GY-HM790, Sony cameras with HDCU-2500


:: Applications of SMPTE 304M and SMPTE 311M Cable Assemblies

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