SMPTE 304M and 311M are not rivals. SMPTE 311M defines the hybrid camera cable, with single-mode fibres and copper conductors in one jacket. SMPTE 304M defines the hybrid connector that terminates it, with fibre and electrical contacts in one shell. A camera-to-base-station link needs both: a 311M cable fitted with 304M connectors. The real choices are termination, gender, length and jacket.
SMPTE 304M and 311M cover different parts of the link
People searching for SMPTE 304M vs 311M usually expect two alternatives. They are two halves of one system. SMPTE 311M describes the hybrid electrical and fibre-optic camera cable. SMPTE 304M describes the hybrid connector that goes on the ends of that cable and on the equipment it plugs into. A complete camera link uses a cable made to 311M and connectors made to 304M.
SMPTE has since added an ST prefix to its document names, so ST 304 and ST 311 are the same documents under newer labels. The older names with the M suffix are still the ones printed on catalogues, drawings and drum labels, and they are the ones buyers type into a search box.
Both documents serve one job in broadcast and live production: joining a system camera to its base station, also called the camera control unit. One cable has to bring the picture and sound out of the camera, deliver power into it, and carry control and return signals in both directions.
SMPTE 304M vs 311M side by side
| Point | SMPTE 304M | SMPTE 311M |
|---|---|---|
| What it is | Hybrid electrical and fibre-optic connector | Hybrid electrical and fibre-optic camera cable |
| What it defines | The shell, the contacts and how plug and receptacle mate | The fibres, the copper conductors and the mechanical build of the cable |
| Fibre content | Fibre contacts that line up with the two single-mode fibres | Two single-mode fibres in the cable core |
| Copper content | Electrical contacts for power and low-voltage lines | Copper conductors for power and control |
| Where it sits | On each end of an assembly, and on camera, base station, wall box and drum receptacles | Between the ends, on a drum or laid in lengths |
| Typical fault | Dirty or damaged fibre contacts, worn or bent electrical pins | Crushed or kinked cable, damaged jacket, broken conductors |
| What you specify | Plug or receptacle, gender, cap, boot and strain relief | Length, jacket material and colour, conductor details, handling needs |
Read across a row and the two columns never compete. You cannot order a 304M instead of a 311M, because one is the plug and the other is the lead it plugs onto.
What the 304M connector fixes
The 304M connector puts the optical and the electrical paths in one metal shell, so a single mating action joins both. The standard fixes the mating interface, which is why a plug from one maker will mate with a receptacle from another, and why camera and base-station makers can fit the same receptacle.
Some practical points follow from that design:
- Plugs and receptacles come in different genders. Assemblies meant to be chained together usually carry a plug on one end and a receptacle on the other.
- The fibre contacts sit inside the shell, where dust and fingerprints collect whenever a cap is left off. Cleaning and inspection belong in every setup routine.
- The connector is often described in catalogues by a maker's part family rather than by the standard number. Ask for the drawing and confirm that the interface is the 304M one.
- The standard covers the connector, not the signal. The format that a camera sends over the fibres belongs to the camera system, so the camera and the base station at each end must be a matched pair.
What the 311M cable fixes
The 311M cable puts two single-mode fibres and a set of copper conductors inside one jacket. The fibres carry the digital camera signals in each direction. The copper carries power from the base station to the camera head and low-voltage lines for control. Putting everything in one cable is what lets a camera run on a single lead with no local mains supply.
Three construction choices matter when you buy:
- Copper size. A thicker conductor drops less voltage over distance, so the camera can be powered further from the base station. It also makes the cable thicker, heavier and stiffer.
- Fibre path. Single-mode fibre has low loss, so the fibres are seldom what limits a run. The mated connections along the way usually matter more.
- Jacket. Cable that is dragged across floors and wound on drums needs a tough, abrasion-resistant jacket. Cable fixed into a building may instead need a low-smoke, zero-halogen jacket to meet the site's fire rules.
For the wider story of how the cable behaves in the field, our guide to SMPTE hybrid cable covers drums, powered length and cleaning in more detail.
How both standards meet on a camera-to-base-station link
Follow the link from the camera outwards and you meet each standard in turn:
- The camera carries a receptacle to the 304M interface.
- A plug on the first assembly mates with it. This is the first mated pair.
- The 311M cable runs from that plug to the next connector, which may be on a drum hub, a wall box or another length.
- Each further join is another mated 304M pair and another place to add loss or pick up dirt.
- The last plug mates with the receptacle on the base station.
The cable has to pass signal and power end to end, and the connectors have to stay clean and seated at every join. A fault anywhere in the chain looks the same from the control room, a dropped or noisy camera, so keep a record of which assemblies make up each run. The fewer joins a run needs, the fewer places there are to look.
Where the fibre and power budgets need checking, the method in our fibre loss budget guide applies to the optical side, with the camera maker's powered-length figure applying to the copper side.
How to choose between the options around 304M and 311M
Since the two standards work together, the decisions sit around them:
- New camera run from scratch. Order a complete assembly: 311M cable with a 304M connector on each end, genders matched to your equipment and to any lengths you plan to chain.
- Fixed infrastructure with installed single-mode fibre. Ask about an assembly that breaks the fibres out to SC connectors at one end, so the fibre can patch into wall boxes, panels or converters. Radix makes SMPTE to SC hybrid cable for this.
- Damaged connector on a good cable. The job is a 304M connector replacement. Check the cable's outer diameter and conductor build so that the new backshell and strain relief fit it.
- Longer run than one length allows. Add lengths with opposite genders at the joins, or order a single longer cable, and check the powered-length limit before deciding.
- Rough outdoor or event use. Choose the jacket for abrasion and flex life, and add dust caps with lanyards and a drum.
If the camera maker publishes a limit for powered cable length or a conductor requirement, write it into the order. The standards make the parts fit together, but they do not promise that every length will power every camera.
What to send us for a quote
Radix makes SMPTE hybrid camera cable assemblies to the customer's drawing. The details below let us quote a build that fits your equipment the first time:
- Assembly length, and the length tolerance you can accept.
- Termination at each end: 304M plug or receptacle with the gender stated, or SC breakout for the fibres.
- Make and model of the camera, base station and any wall box or drum receptacle the assembly mates with, ideally with a photo of the receptacle.
- Jacket material, colour and any fire rating the site demands.
- Drum or coil, and the hub connector if a drum is used.
- Dust caps, lanyards and labelling, including the assembly number.
- Maximum insertion loss per mated connection and the test report you want, with copper continuity checks.
Our page on broadcast and live production lists what we build for that sector. Send the build details through the request a quote page, and ask for the loss figures and lead time in the quote itself.
Questions buyers ask
Is SMPTE 304M the same as SMPTE 311M?
No. SMPTE 304M defines the hybrid connector. SMPTE 311M defines the hybrid camera cable. They are written to work together, so one camera link normally uses a 311M cable terminated with 304M connectors.
Which one is the connector, 304M or 311M?
The connector is 304M and the cable is 311M. The connector sits on the ends of the cable and on the camera and base-station receptacles.
Do I need both 304M and 311M?
For a standard camera-to-base-station link, yes. The cable carries the fibres and copper, and the connector joins them to the equipment. If you only need the fibres on fixed infrastructure, an assembly with SC breakout at one end may suit instead.
Can a 311M cable use a different connector from the 304M?
Yes. The cable can be terminated differently, for example with its two fibres broken out to SC connectors for patching into installed single-mode fibre. The copper is then connected or powered separately. Camera equipment that has a 304M receptacle still needs a 304M plug.
Does the cable standard decide which camera system I can use?
No. The cable and connector standards make the physical link interchangeable. The signal format sent over the fibres is set by each camera maker, so the camera and base station at the two ends must belong to the same system.
What do I send to get the right gender and length?
Send the make and model of the camera, the base station and any drum or wall box, with a photo of each receptacle if you can. Add the length you need and whether lengths will be chained, and we can confirm the plug and receptacle arrangement in the quote.