A SMPTE hybrid camera cable carries two single-mode fibres and several copper conductors, and its connector (the SMPTE 304M type) puts the optical contacts and the power contacts in one threaded housing. The camera end and the base-station end differ in shape. Check the gender, the optical cleanliness and the copper voltage drop before the first shoot.
Start with the link, not the connector
A studio or outside broadcast camera on a hybrid link has a camera head at one end and a base station (often called the CCU or camera control unit) at the other. A single SMPTE hybrid cable joins them. It carries the video and control on optical fibre and the camera's power on copper, so the camera needs only one cable run. The cable construction is described in the guide to SMPTE hybrid cable. This page is about what sits on each end.
Two standards are involved, and they are often confused. SMPTE 311M describes the hybrid cable, which holds two single-mode fibres and a set of copper conductors in one jacket. SMPTE 304M describes the hybrid connector that fits it. The difference between the two documents is covered in the guide to SMPTE 304M and 311M. In short, a cable can meet 311M and still be fitted with a connector from a different family, so a purchase order has to name the cable and the connector separately.
Radix Fibrotech makes SMPTE hybrid camera cable assemblies to the customer's drawing in Pune. The product pages for SMPTE hybrid cable and the SMPTE SC hybrid cable show the two main termination styles. The broader context for studio and field work is on the broadcast industry page.
What one hybrid connector contains
A hybrid connector is a multi-contact connector with two kinds of contact in the same shell. The shell is circular and coupled by a threaded ring. Inside it are:
- two optical contacts, one for each fibre, each holding a precision ferrule that mates against its partner;
- a group of electrical contacts for the copper conductors, which carry power to the camera and, in some designs, low-speed signals;
- a keying feature, so the two halves can be joined in one orientation only;
- a coupling nut, a seal where the design has one, and a dust cap.
The fibre on a SMPTE hybrid link is single-mode (OS2 type, 9/125 micron). One fibre carries the signal toward the base station and the other carries it back, so the two fibres work as a pair. That pairing matters at the connector, because the two fibres are not interchangeable. Crossing them stops the link.
The exact number and size of the copper contacts, and the pin allocation, vary by connector family and by the camera maker. Take them from the connector data sheet and from the camera manual. Do not assume that two connectors from different makers are pin-compatible because they look the same.
The two ends are not the same
| Point on the link | Typical connector | What it does | What goes wrong |
|---|---|---|---|
| Camera head | Fixed receptacle on the camera body, mating with a free cable plug | Takes the full load of repeated plugging and the weight of the cable | Worn contacts, bent pins, dirt in the optical face |
| Base station | Fixed or panel receptacle, sometimes a cable-mounted socket | Sits in a rack or a truck, less movement | Wrong gender, the cable's other end was made for the camera side |
| Extension joint | A cable-mounted plug on one hybrid cable mating with a cable-mounted socket on the next | Joins two lengths in the field | Adds two optical interfaces and two copper interfaces to the loss budget |
Because the two ends are made differently, a cable has a camera end and a base-station end, and the ends are not usually swappable. When you order, name the end explicitly on the drawing as "camera end" and "base-station end", with the connector family and gender for each, and mark the same words on the cable's boots with a label. A cable that is correct in every other way but reversed will not plug in at the far end, which wastes a day on a live job.
Some systems use an adapter set, a plug-to-plug coupler or a short jumper, to mate two ends of the same type. Each adds loss and a potential contamination point. Use as few as the design allows.
The optical contacts
Each optical contact holds a small ferrule. The two ferrules meet inside the coupled connector, and the light passes from one fibre core to the other across the mated joint. Everything that was true for ordinary fibre connectors is true here as well, only in a harsher setting.
- Cleanliness. A film of dust or skin oil across a single-mode core, which is about 9 micron wide, causes loss and reflections. A hybrid connector on a camera is unplugged and replugged far more often than a rack patch cord, and it is carried on a hot, dusty set. Clean it before every mating.
- Dust caps. Both the plug and the receptacle need a cap whenever they are not mated. A lost cap is a lost connector in practice.
- Cleaning access. The optical contacts sit recessed inside the shell, so a standard 2.5 mm stick cleaner may not reach them. Ask the connector maker which cleaning tool fits, and keep that tool in the camera kit.
- Polish. Single-mode contacts are polished either flat-with-curve (UPC) or angled (APC). Mating one with the other does damage and adds loss. The connector family and the camera system decide which polish is used, and the polish should appear on the drawing. The mismatch problem is explained in the guide to APC to UPC mating mistakes.
The principles of end-face inspection and cleaning are the same as for ordinary connectors. The guide on connector end-face cleaning and inspection goes through a dry and wet method, and the inspection tool shows contamination you cannot see.
The copper contacts
The copper side of the connector is simpler than the optical side but is the one that fails more visibly. A camera that powers off in the middle of a shoot usually has a copper problem. Power contacts are rated for a current. Pin sockets weaken with wear, and a pin socket that has opened up will arc or heat under load.
The copper run also has a resistance, and resistance drops voltage. The worked example below shows the sum. All values are assumptions for illustration. Take the real conductor size and the camera's minimum supply voltage from the data sheets.
| Quantity | Assumed value |
|---|---|
| Power conductor cross-section | 1.5 mm² per conductor (assumed) |
| Copper resistivity at 20 °C | 0.0172 ohm mm² per metre |
| Cable length | 300 m |
| Supply and return path | 2 conductors, so 600 m of copper in the loop |
| Camera current | 2.0 A (assumed) |
| Supply at the base station | 48 V (assumed) |
Loop resistance is 0.0172 x 600 / 1.5 = 6.88 ohm. The voltage drop at 2.0 A is 2.0 x 6.88 = 13.8 V, so the camera sees about 34.2 V. If the camera needs at least 36 V to run, this link fails even though the fibre is perfect. Doubling the conductor size to 3.0 mm² halves the drop to 6.9 V, and the camera sees 41.1 V. If the cable construction cannot change, the options are to shorten the run, raise the supply voltage if the system allows it, or use two conductors in parallel per leg if the design provides spare conductors.
The connector contributes a small resistance of its own, usually in the milliohm range per contact, which is negligible next to the cable. A badly worn contact is the exception, and it shows up as a hot connector shell after a few minutes of running.
Optical budget for a hybrid link
Loss on the fibre is simple. Add the fibre attenuation to the connector losses. All figures here are assumed for the example, not Radix values, and the real numbers come from the data sheets and the system manual.
| Item | Assumed loss | Count | Total |
|---|---|---|---|
| Single-mode fibre at 1310 nm | 0.4 dB/km | 0.3 km | 0.12 dB |
| Hybrid connector pair (camera end) | 0.5 dB | 1 | 0.50 dB |
| Hybrid connector pair (base-station end) | 0.5 dB | 1 | 0.50 dB |
| Extension joint (two connector pairs) | 0.5 dB each | 2 | 1.00 dB |
| Total | 2.12 dB |
The camera maker states how much loss the optics can tolerate. Subtract the link loss from that figure to see the margin. The extension joint is the item that surprises people. It looks like a small thing, but it takes up almost half the budget in this example. The guide on fibre loss budgets sets out the method, and the fibre loss budget calculator does the sums.
Which termination style to choose
There are two common ways to terminate a hybrid cable, and which one you pick depends on the equipment at each end.
| Style | What it is | Suits | Watch for |
|---|---|---|---|
| Full hybrid connector | Fibre and copper in one connector shell on the cable end | Camera heads and base stations that accept a hybrid socket | The shell family must match the socket exactly |
| Breakout to separate connectors | Fibres brought out to optical connectors such as SC, copper to a power connector, from a fan-out at each end | Systems that take optical and power on separate ports | Fan-out leg lengths, strain relief at the break, more items to stow |
The breakout style needs more legwork, but it is useful when the system has separate optical and power ports. The SC variant is described on the SMPTE SC hybrid cable page. Make sure the drawing shows the leg lengths from the fan-out to every connector.
Checking a connector before a shoot
- Inspect the shell for dents, a bent coupling thread and a cracked boot. A damaged thread causes a half-seated connector and a link that drops when the cable is nudged.
- Remove both dust caps and keep them in a labelled bag.
- Inspect the optical faces with a scope. Clean, then inspect again. Do not rely on a first clean alone.
- Look at the copper contacts for burn marks, bent pins and green or white corrosion.
- Check the gender and the end label so the camera end goes to the camera.
- Mate the connector by hand and tighten the coupling ring fully. A partly tightened ring is the most frequent cause of an intermittent link.
- Test the fibre with a light source and power meter, or with the camera system's own link indicator, before the cable is dressed and taped down.
- Record the cable ID and test result. If a cable fails on the day, you know which one to pull.
Mistakes that cost a shoot day
- Specifying only the cable standard. Saying "311M hybrid" without the connector family and gender leaves the supplier to guess.
- Swapping the ends. If the camera end and the base-station end are not labelled, a cable gets reversed on site and will not mate.
- Ignoring voltage drop. A 300 m run is fine for some cameras and a failure for others. Do the sum, as in the worked example.
- Cleaning too little. A camera link is mated more times in a month than a data centre patch cord in a year. Treat cleaning as a routine, not a repair.
- Dragging the cable by its connector. The strain relief takes the load on a well-made assembly, but a connector that is dragged across a floor wears at the shell and the optics.
- Coiling too tightly. A hybrid cable has copper conductors that stiffen it, and a tight loop damages the fibre. Follow the bend radius on the cable data sheet.
What to put on the order
A complete order for a SMPTE hybrid assembly lists the following.
- Cable type and standard (SMPTE 311M or the specific cable data sheet).
- Fibre type: single-mode OS2, and the polish the system needs.
- Connector family and gender at the camera end.
- Connector family and gender at the base-station end.
- Length in metres, measured between connector shells, with the tolerance you will accept.
- Jacket type and colour, with a note on whether the cable will be dragged, reeled or fixed.
- Labels for the cable ID and for each end.
- Test requirements: loss at 1310 nm, and the report format.
- Whether dust caps and a carry bag are included.
Send the drawing with those items through the request a quote page, by phone or WhatsApp. For fixed studio and pan-tilt-zoom camera runs, the guide on camera fibre cable for PTZ and studio adds details on routing and slack.
Questions buyers ask
What is the SMPTE hybrid connector?
It is a circular multi-contact connector that holds two single-mode optical contacts and a group of copper contacts in one shell. It is defined by SMPTE 304M and is used on camera cables so that the video fibre and the power copper run through one connection.
What is the difference between SMPTE 311M and 304M?
SMPTE 311M describes the hybrid camera cable, with two single-mode fibres and copper conductors. SMPTE 304M describes the hybrid connector. A purchase order should name both, because a cable can be fitted with more than one style of end.
Are the camera end and the base-station end the same?
Usually not. One end is made to plug into the camera head, the other into the base station or an extension joint, and the two differ in gender and shape. Label each end on the drawing so the cable is not reversed on site.
How do I clean the optical contacts on a hybrid connector?
The contacts are recessed in the shell, so use the cleaning tool the connector maker names, then inspect the face with a scope. Clean before every mating, and cap the connector whenever it is open. The general method is in our end-face cleaning guide.
How long can a SMPTE hybrid cable be?
The fibre can run for kilometres, but the copper limits the length for powered cameras because of voltage drop. Work out the drop from conductor size, current and length, and compare it with the camera's minimum supply voltage. The example above shows the sum.
Can I join two hybrid cables to make a longer run?
Yes, with an extension joint, but each joint adds two optical interfaces and two copper interfaces. Add the loss to the optical budget and the resistance to the voltage-drop sum before you commit to the longer run.
Does the polish matter on a hybrid connector?
Yes. Single-mode contacts are either UPC or APC, and mating one with the other causes damage and loss. Take the polish from the camera system's manual and write it on the drawing.
Can Radix make hybrid camera cable assemblies?
Radix makes SMPTE hybrid camera cable to the customer's drawing in Pune. Send the drawing with the connector family, gender at each end, length and test needs through the quote page, and we reply with the details.