Signal cabling
BNC and SDI coax: identify the entire video run
“BNC” describes a connection, but does not establish the video capability of an assembly. Before preparing an SDI line, identify the cable, connectors, accessories, and intended signal from output to final input.
Read the complete cable part number
Belden identifies 1694A as 75 Ω SDI coax. To check another cable or a finished assembly, record the jacket marking, variant, and connectors, then consult their specific data sheets.
- Record manufacturer, part number including suffix, length, and ends. Do not identify cable solely as RG-6 or “for 4K.”
- Photograph labels without forcing or opening connectors. Flag crushed jackets, cuts, or loose connections for evaluation.
- Request resolution, frame rate, and output format, as well as the SDI standard or rate stated by the devices.
A BNC that fits does not confirm impedance
Amphenol RF warns that mixing 50 Ω and 75 Ω connectors can degrade the signal even when they mate. Verify part numbers in the documentation. Neutrik publishes a cable-to-connector table: a BNC for another diameter or construction cannot be selected by appearance.
| Component | Record | Decision |
|---|---|---|
| Main cable | Part number and actual length | Compare with documented signal and conditions |
| Connectors and joints | Each BNC, coupler, and patch model | Verify suitability for the assembly |
| Devices | Output, input, and selected format | Confirm complete-link compatibility |
Measure and prepare every part of the link
Review the complete route at the intended signal rate. A value in a cable chart does not replace transmitter, receiver, or accessory requirements. If the documentation does not show that the assembly is suitable for the run, ask for an evaluation of another way to carry the signal before adding adapters.
- Draw output → cable → patch points or couplers → input. Include the short leads often omitted from measurements.
- Compare a direct run with a sectional route. Joints may help accommodate changes but add components to check.
- Review bend radius and conditions of use for the exact cable. Protect it from wheels, doors, and pulls at equipment.
- Label source and destination. Distinguish the roles of multiple lines and any backup.
Check the format that will actually be used
Arrange a check with the actual source and destination, the entire route, and the planned format. Record whether the signal remained stable, any dropouts, and the test conditions. A result at another rate or with a short jumper does not validate the event link.
- Save the result against the cable and link IDs.
- To isolate a fault, substitute one component at a time with a verified equivalent.
- Set aside intermittent assemblies; do not return them to available spares without evaluation.
Setup questions
Does a BNC connector make the cable SDI-ready?
No. Verify the cable and termination part numbers. BNC connectors appear in systems with different functions and impedances.
Can I join two cables and retain each cable’s reach?
Passive cable reaches cannot be added together. Review the total length, coupler, and complete assembly at the planned signal, then check the whole run.
Does passing HD confirm a more demanding signal will pass?
No. Identify the event’s required format and rate and check the documentation. Keep the result for each configuration without extending it to others.
Sources and documentation
- Belden — 1694A Technical Data Sheet · Official documentation
- Neutrik — BNC Cable to Connector & Connector to Cable Guide · Official documentation
- Amphenol RF — Can I use 50 ohm connectors in a 75 ohm system? · Official documentation
Keep planning the event
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