And how long can the sdi cable be before it affects the picture quality?
Thanks in advance!
If the circuit is SMPTE 259 compliant, over 1000feet with the proper cable. Some of these HT SDI mods and cards may not however have equalizer chips to keep costs down. That's still OK since you should be able to go 50feet with plain old RG59.
As for picture quality, SDI or digital is a totaly different animal. Analog gets softer and noisy with legnth. A digital signal suffers from what is called a "cliff effect". That is a perfect signal then nothing. In reality borderline signals will have intermittent hits and pixel breakup.
On thing I have not seen discussed in all these SDI threads is that the SDI signal is scrambled. It's not a simple but fast UART like you PC serial card has. Because the clock must be extracted fromt the signal, the data must be a fairly even mix of ones and zero's. If you had a black picture for example, the clock could not be recovered and the receiver would free-run until a suitable bit pattern arrived. So to avoid this SDI adds polynomials to the data to mix it up and produce a good mix of ones and zeros. The receiver simply adds the inverse polynomial back to descramble it. This scrambling has nothing to do with any form of copy protection. It's a widely used technique in high speed data paths.
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