HD SDI cable length

	Re: HD SDI cable length by gary adcock on Oct 24, 2009 at 2:07:06 pm [Scott M. Douglas] " I get a picture and it looks OK. What gives? Why is it working? " if you put a scope on both ends of that cable you will see why. its not that longer cables don't carry the signal, its about how much quality is lost over the interference and signal loss with longer cables. run a power cord around that box and see what the output does... gary adcock Studio37 HD & Film Consultation Post and Production Workflows for the Digitally Inclined Chicago, IL http://library.creativecow.net/articles/adcock_gary/AJAIOHD.php Respond to this post   •   Return to posts index

	Re: HD SDI cable length by Bob Zelin on Oct 24, 2009 at 2:31:48 pm Hi Scott, you can go to Radio Shack, buy an RCA to RCA audio cable, put RCA to BNC adaptors on each end, and plug them into your camera and monitor and get a picture. You can then shoot your HD job, and take the firewire out of your camera or deck, go into a bare bones MAC Pro via firewire, do the whole job in HDV codec, and deliver your DVD (or data delivery) to your client - see, now you are a hi end pro doing HD production, and your investment is a Radio shack audio cable, and the smart savvy use of your MAC Pro. RG6 is not Hi def cable. Hi Def video cable is double shielded cable (like Belden 1694A). You can use "thinner cable" as well (like RG59 that you saw at Home Depot) - but the hi def version is also double shielded cable (like Belden 1505A or Gepco VPM2000). And there is even thinner cable (called RG-174U), which in it's pro version is ALSO double shielded and approved for HD use, like Belden 1855A. And EVEN THINNER HD CABLE like Belden DT174. But you want to know WHY go thru this effort ? A SD-SDI or HD-SDI signal is a SQUARE WAVE DATA SIGNAL. This signal degrades over the length of the cable (the squares become less square), and the signal gets harder and harder to read (meaning the video switcher, or editing system, or HD VTR can't distinguish the mess coming down the cable- it's no longer clean square waves). Here is a typical example - You run a 100' RG59 cable (not double shielded) from your camera to a video patch bay. You loop on the bottom jack of the patch bay back to your monitor, which is right next to you (also 100' away) using the same standard RG59 cable (not double shielded). Now, you don't get a picture. And you say "gee, what happened". The longer the cable, or the worse quality of the cable, the signal (the square wave) starts to degrade. You start to get jitter in the signal, instead of a nice clean square wave with sharp edges that can be seen by the equipment you are sending it to. This happens even WITH THE BEST CABLE, after a certain distance. And if you don't use double shielded cable, the signal is prone to interference (just like Gary's example of the power cable), so things like power, dimmer circuits, and other audio and video signals crosstalk will now start to affect the signal in your cable, making it unreadable by the video switcher, editing system, or HD VTR you are trying to feed. In professional enviornments that run long distances with these signal, professionals own video waveform monitors with EYE PATTERN analysis, that lets you observe the shape and condition of the HD signal, to see if your "square waves" are degrading. Because even with the best gear, and the best cable, if you don't meet the distance specification of the cable, you can be SCREWED, and everything will stop working. There is NO video cable out there (even Belden 1694A) that will continue to work reliably at distances of 640' without a reclocking amplifier. The only way to do this is with Fibre. Belden 1694A is spec'ed at 360', and you are just looking for trouble by exceeding these distances. There is nothing like hooking up five 600' cables from your HD cameras to your HD switcher in a sports stadium, and having everything stop working, because of the unreliability of the signal coming in from the cameras - due to cable legnth. These are not urban legends. bob Zelin Respond to this post   •   Return to posts index

	Re: HD SDI cable length by maurice jansen on Oct 24, 2009 at 9:35:18 pm hi there. if you put a signal analyzer to the end of the spool of RG6 i guess it will report several error in a particular timespan. an error can be this little that it will not be spotted. (like a white glitch on a white background for instance) but can be fatal if it will be seen by the reciever as a TRS. one thing to remember is that the cable is not installed yet. Tiewraps CTP's wrong handeling will introduce extra returnloss. reclocking can help but has to be done with common sense. reclocking when the signal is in a bad state will introduce extra jitter on the signal. you can't do this for ever. i have no experience with Cat extenders. greet Maurice Respond to this post   •   Return to posts index

	Re: HD SDI cable length by Bob Zelin on Oct 24, 2009 at 9:55:57 pm a cheap HD Video DA (like a $250 AJA HD5DA) will reclock your signal. Bob Zelin Respond to this post   •   Return to posts index