Heapsy Posted January 24, 2007 Share Posted January 24, 2007 I read this on another thread If you have a single bit of gear at the end of your cable, that gear is your termination. Where the need for external terms comes up on video gear is where you have the ability to loop a signal through several bits of gear, or attempt to use a "T" connector on a coax video feed. The other place where a term would be appropriate is if you use a splitter on a VGA feed and have a spare output...such a spare should not be left unterminated. Bob I have a coax DA for composite video which has 10 outputs on it, I'm currently only using 6 outputs and the other 4 are sitting empty. Does this mean I should be using a 75 ohm terminator (No Arnie jokes! ) on each of these and what will this actually do to the image on the other outputs?Thanks in advance, Mark Link to comment Share on other sites More sharing options...
Toxopholist Posted January 24, 2007 Share Posted January 24, 2007 There is no need to terminate unused outputs on a da, as each output can be treated as a seperate device, the only place you really need to use termination is on the end of a chain of devices, and more often than not devices that go on the end of a chain terminate themselves either automatically or via a switch. Link to comment Share on other sites More sharing options...
Fletch Posted January 24, 2007 Share Posted January 24, 2007 Was about to post the same thing - I agree with Toxopholist. CheersFletch Link to comment Share on other sites More sharing options...
Peter F Posted January 24, 2007 Share Posted January 24, 2007 Was about to post the same thing - I agree with Toxopholist. CheersFletchI also agree with Toxopholist but just because I can add something that might be useful if someone googles for this in the future, I will! If the input to the DA has a loop output on it and you aren't using it then best practice would be to put a terminator on the unused loop output. The same applies to other pieces of equipment e.g. monitors with a loop through connection on them. Quite often you will find a switch marked 75ohm/Hi-Z located next to the loop connector. Selecting 75ohm will have the same effect as physically connecting a 75ohm terminator on the output. You must select Hi-Z if you are using the loop output. Failing to do so could introduce the concept of double terminating (which I believe Bobbsy or someone else sensible mentioned in another thread). You do not want to double terminate. Cheers,Peter Link to comment Share on other sites More sharing options...
Toxopholist Posted January 24, 2007 Share Posted January 24, 2007 I also agree with Toxopholist but just because I can add something that might be useful if someone googles for this in the future, I will! If the input to the DA has a loop output on it and you aren't using it then best practice would be to put a terminator on the unused loop output. Cheers,Peter Unless it has a termination switch on it... charlie Link to comment Share on other sites More sharing options...
Heapsy Posted January 25, 2007 Author Share Posted January 25, 2007 Thank you very much! Mark Link to comment Share on other sites More sharing options...
Bobbsy Posted January 27, 2007 Share Posted January 27, 2007 I only just noticed this thread...and it was a quote from me that started it! In my experience the answer isn't quite as clear cut as has been presented here. Over the years I've certainly encountered models of equalising VDA that specified all unused outputs should be terminated for optimum reliability.....and I've gone through hundreds of BNC terms to do this! Manufacturers that spring to mind are Avitel and Link (but please don't ask me for the exact models as the paperwork that would have these is well buried!). When in doubt, check the manual but if your not having problems without them, you're probably okay. Bob Link to comment Share on other sites More sharing options...
dbuckley Posted January 27, 2007 Share Posted January 27, 2007 There is a technical answer to this question. If the DA is one amplifer followed by a resistive splitter network feeding several outputs, then termination of all outputs is required to keep the resistive network operating as it should. Thus unused outputs should have a terminator thingie on them. If the DA uses one active amplifier for each output, then terminating unused outputs is unnecessary. By the same token if you are distributing RF using CATV splitters then they should have unused outputs terminated. Link to comment Share on other sites More sharing options...
David Duffy Posted January 27, 2007 Share Posted January 27, 2007 If the DA is one amplifier followed by a resistive splitter network feeding several outputs, then termination of all outputs is required to keep the resistive network operating as it should. Thus unused outputs should have a terminator thingie on them. If the video DA uses a "double terminated" (75R series output impedance with 2x gain) style output stage (even with a single amplifier) then unterminated outputs will not be a problem. I've built and sold heaps of video DA's like this over the years and can confirm this. There may be some designs that require termination but I suspect they're in minority these days. RF splitters can be a different kettle of fish though. Link to comment Share on other sites More sharing options...
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