HDTV is a digital television broadcasting system with a resolution that is higher than the analog television systems NTSC, SECAM and PAL. Since the digital transmission format uses video and image compression, HDTV systems can use channels with lower bandwidth compared to analog television.
1.5 Gbps HD-SDI
Systems from S1 to S3 can be transmitted over a single HD-SDI channel described in the SMPTE 292M specification, which operates at a nominal data rate of 1.485 Gbps in 8-bit and 10-bit resolutions. SMPTE 292M defines the coaxial interface and SMPTE 297M defines the optical interface.
3 Gbps HD-SDI
S1 to S4 systems can also be transmitted over single-channel HD-SDI, described in SMPTE 424M-2006, which operates at a nominal data rate of 2.97 Gbps at 10-bit resolution. There is also an optical transmission specification for this interface (SMPTE 297M-2006).
When using this “3G-SDI” interface, the following precautions must be observed:
Length of the coaxial cable
With the 3G-SDI interface, special attention should be paid to the type, quality, and length of the coaxial cable.
Note that, depending on the devices used, a coaxial cable with an operating length of 70 to 140 meters is required. Passive components such as patch panels and connectors to coaxial cables can significantly affect the maximum cable length.
3G-SDI display levels
The 3G-SDI interface allows for two different displays of the image format described in the SMPTE 425-2008 specification. This choice of level also affects the number of embedded audio channels that can be transmitted in the interface. Users and interface designers should pay special attention to ensure that their production equipment supports the levels required in operation.