To Retrofit or Not
As mentioned, SD/HDSDI is transmitted over coaxial 75 Ohm cables. Many facilities are wired by the mile with video cable from previous installations. If you are considering upgrading your existing infrastructure it is tempting to re-purpose the BNC terminated video cable.
The short answer to this question of “can I reuse my existing video coax for SDI?” is maybe. It is true that implementing a SDI format over cable that once carried composite signal is viable. If the system is to be upgraded to carry the latest HDSDI problems arise.
The issue here is that in most cases the quality and gauge of wire used in the past cannot sustain the bandwidth needs. In a facility where HDSDI is desired or required, the best practice is to re-run or run anew with modern compliant cable.
Testing the Infrastructure
Still unsure if your copper infrastructure is capable of carrying the bit rates necessary? A host of test equipment manufacturers make equipment which can analyze, monitor and record results.
While the specifics of the test procedure and its elements are beyond the scope of this article, the visual results can be summarized simply. The Oscilloscope reading either shows a crossover signal with a wide open eye, good, or bad. This test and record should be provided by any integrator looking to provide open and transparent bid documentation.
The Fiber Option
What about using fiber topology? Regardless of the coax capabilities there is a fairly hard limit of about 300 ft total transmission run. This solution is especially useful with a facility that has a studio and transmission room on opposite sides of campus.
Fiber, of course, can make far longer runs than any copper solution, you are only limited by the number of repeaters a system can include. How does one integrate this with HDSDI? The solution is simpler than one would expect, by utilizing ‘drop boxes’ manufactured by a host of third party companies. The boxes take in SD/HDSDI and convert the signal to fiber or vice versa.
What Gear Connects
The topic of drop box solutions touches on the issue of just what equipment utilizes SD/HDSDI. As the format was specifically designed for broadcast use it will not be found on any consumer level playback sources or monitors. A critical issue for institutions is the need to maximize existing equipment in any upgrade process.
In the same manner as the fiber conversion units, many manufacturers sell conversion boxes that take SD/HDSDI to HDBaseT, component, Displayport and analog.
Right For You?
In the end, is SD/HDSDI right for your installation? If you need broadcast quality video that can be synchronized in professional studio environments, this is the format for you.
More likely than not, any installation of the SDI video topology will involve a hybrid system delivering video to various levels of destinations.
With any installation, research on the specifics and site testing is essential.
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