SMPTE hybrid cable is the broadcast camera cable defined by SMPTE ST 311 (formerly 311M). It carries two single-mode fibres for signals in each direction, plus copper conductors for power and control. It terminates in the hybrid connector defined by SMPTE ST 304 (formerly 304M), usually of the LEMO 3K.93C type, and links a system camera to its camera control unit (CCU).
What SMPTE 311M and 304M define
SMPTE ST 311 specifies the hybrid camera cable: its fibres, its copper conductors and its mechanical construction. SMPTE ST 304 specifies the connector that terminates it, with two fibre contacts and four electrical contacts in one metal shell. Both were first published as 311M and 304M, and the old names are still used in catalogues and on drum labels.
The standards make the physical link interchangeable. A SMPTE hybrid cable built to ST 311 and ST 304 will mate with any camera or CCU fitted with the standard receptacle. The signal format sent over the fibres is not standardised in the same way: each camera maker uses its own transmission scheme between its camera and its CCU. So the cable is shared across brands, but the camera and CCU at each end must belong to the same system.
What the hybrid cable carries
| Element | Quantity | Job in the camera link |
|---|---|---|
| Single-mode fibre | 2 | One fibre in each direction. Camera to CCU: programme video, audio and data. CCU to camera: return video, intercom, tally, sync and remote control, multiplexed by the camera system. |
| Power conductors | 2 | Carry power from the CCU to the camera head, so the camera needs no local supply. |
| Low-voltage conductors | 2 | Control and signalling, used in different ways by different camera systems. |
| Strength members and jacket | Not applicable | Aramid or similar strength members and a tough outer jacket, often polyurethane, for repeated deployment. |
Using single-mode fibre means the fibre itself is rarely the limit on distance. Moving all signals onto fibre also removes the ground loops and interference problems of older multicore copper camera cable.
How a camera-to-CCU link works
The CCU sits in the outside broadcast truck, production gallery or flypack. The camera sits on a tripod, pedestal or a camera operator's shoulder, anything from a few metres to a long way across a stadium. One hybrid cable joins them, sometimes made up of several lengths connected end to end, and sometimes passing through a wall box or patch panel on the way.
Two things set the maximum length:
- Power. Voltage drops along the copper conductors. The heavier the camera load, including lens, viewfinder and accessories, the shorter the powered length. Camera makers publish the maximum powered cable length for each camera and CCU pairing, and many CCUs check the cable before applying full power.
- Optical loss. Each mated SMPTE connection adds loss, as does any dirt on the fibre contacts. Several joins in a long run can use up the optical budget of the camera system even when the power budget is fine.
Where a run is too long to power from the CCU, many systems can run the camera from a local power supply and use the fibres alone. That extends reach a long way, because single-mode loss over distance is low.
Dirty fibre contacts are the most common cause of SMPTE link faults. The fibre contacts in a 304M connector sit inside the shell and collect dust whenever caps are left off. Cap every connector when unmated, and clean both halves with a cleaner made for the hybrid connector before each use.
304M connectors versus SC terminations
The 304M connector is built for the field. It mates the fibres and copper together in one action, latches with a push-pull sleeve, and its metal shell takes knocks and weather. Assemblies are normally built with a male connector at one end and a female at the other, so that lengths can be joined directly. Confirm the genders against the camera and CCU receptacles, and any drum or panel connectors, before ordering.
Some installations break the fibres out to standard SC connectors instead. This suits fixed infrastructure: a stadium or studio where the camera signal travels over installed single-mode fibre between a wall box and the CCU, or where a converter or fibre-only adaptor sits at one end. The copper is then either broken out separately or powered locally at the camera.
| Termination | Carries | Suited to |
|---|---|---|
| SMPTE 304M hybrid connector | Two fibres and four electrical contacts | Camera to CCU links, outside broadcast, studios, events |
| SC fibre breakout | Fibres only, on standard SC connectors | Patching into fixed single-mode infrastructure, panels and converters |
Radix makes SMPTE hybrid camera cable assemblies and SMPTE to SC hybrid cable for both arrangements.
Drums, reels and lengths
Field SMPTE cable usually lives on a drum. A drum with a connector mounted at the hub lets the crew plug the inner end into the hub panel and pay out only as much cable as the shot needs. Things to settle when ordering a drum:
- Cable length per drum, and whether lengths must chain together for longer runs.
- Drum style: open frame or enclosed, with or without brake and winding handle.
- Total weight, which decides whether one person can carry it.
- Hub connector type and gender, and how the free end is protected when wound in.
Radix supplies cable drums and reels for harsh environments, built with the cable and connectors as one assembly.
How to specify SMPTE hybrid cable
- Cable to SMPTE ST 311, with jacket material and colour.
- Length and length tolerance for each assembly.
- Termination at each end: 304M plug or receptacle with gender stated, or SC breakout.
- Drum or coil, and hub connector if a drum is used.
- Dust caps on both ends, with lanyards for field use.
- Labelling for length and assembly number.
- Test report: optical insertion loss for each fibre, and copper continuity and insulation checks.
Ask for the insertion loss per mated connection in the quote, so the full run can be checked against the camera system's optical budget. See how Radix works with broadcast and live production teams, then send the build details through the quote form.
Questions buyers ask
Is SMPTE hybrid camera cable single-mode or multimode?
Single-mode. SMPTE ST 311 cable carries two single-mode fibres, one for each direction, alongside the copper conductors. That is why the fibre path itself supports long runs and why single-mode cleaning and inspection practice applies to the connectors.
Can one SMPTE cable be used with any brand of camera?
Physically, yes, if both ends use the standard 304M connector. The signal over the fibres is specific to each camera maker, so the camera and CCU must belong to the same system. The cable and drums can be shared across systems.
How long can a SMPTE camera cable run be?
Powered length depends on the camera's power draw and the CCU's supply, so it is set by the camera maker for each pairing. If the camera is powered locally, the fibres alone can run much further. Each join also adds optical loss, which should be checked against the system budget.
Are SMPTE 311M and SMPTE ST 311 the same standard?
Yes. SMPTE renamed its standards with an ST prefix, so 311M became ST 311 and 304M became ST 304. Catalogues, drawings and drum labels still use both forms.
Why does a SMPTE camera link fail intermittently?
The usual cause is a dirty or damaged fibre contact in a 304M connector, often at a join between two lengths. Crushed cable and damaged copper pins come next. Clean and inspect every connection in the run, starting with the joins most often handled.
Can SMPTE hybrid cables be joined end to end?
Yes. Assemblies are normally built with opposite genders at each end so lengths connect directly. Every join adds a mated pair to the optical loss, so keep the number of joins as low as the job allows.