Canary SDI 3G BNC Connectors

3G-SDI uses a coaxial interface for the distribution of video signals in broadcast environments. Coax-based 3G-SDI networking uses Emitter-Coupled-Logic (ECL) a high-speed technology with a propagation speed of under 2 nanoseconds. The system impedance is 75 Ohms  and the input/output voltages may be up to 0.8 volts. Transmission along the lines is unidirectional. Coaxial cables used for 3G-SDI are terminated with the  BNC connectors described above.

An impedance of 75 Ohms.

• The attenuation in decibels should be proportional to the square root of the  frequency transmitted, especially for longer cable lengths.

On this basis, SDI uses RG 59U or RG-6 cable. RG-179 may also be used for shorter runs. The SMPTE standard states that the use of 50 Ohm BNC connectors with 75 Ohm cable is not compliant, though this practice has been used for lower bandwidth composite video. The cable should be stored and handled properly to ensure that any signal degradation is minimized.

The video is encoded and the serialized data is scrambled before being transmitted as a bitstream down the coax cable. The SDI data payload includes the syncing, Timing Reference Signals (TRS) for the video and active video data is transferred at speeds between 143 Mbps and 3 Gbps. Ancillary data can also be simultaneously transferred in areas of the data stream not occupied by the video.

Other standardized physical layer SDI components that work with BNC connector cables include:

• SDI Transmitters or Serializers are devices that are capable of integrating a range of signal components and audio processing for fast and effective video streaming, which saves cost and power.
• SDI Cable Drivers  are designed to drive SDI signals along a longer length of coaxial cable. They work to overcome the signal attenuation that takes place with long lengths of coax cable.
• Cable Equalizers are SDI components that compensate for coax cable losses along their length. They can be multi-rate and multi-channel and are used particularly with High Definition (HD) and Ultra High Definition (UHD)  video equipment.
• Reclockers are used to retrieve a clean time sequence or clock from an SDI video that has been affected by jitter. The video can then be re-synchronized.