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Dodgey way to switch HD SDI
Ok so just wanted to know if you can simply switch between 2 HD SDI feeds down into 1 HD SDI feed through a composite BNC switch. As far as I can tell they both use 75 Ohm cables and connectors. I tried with a random RCA switch I had and my end device saw them both perfectly when I made the switch, so it does seem to work, just don’t understand the unseen problems I may be causing? I literally only need to switch between these 2 cables for now, and am trying to use a very cost effective method. I know its not even close to a professional method.
Mac Pro 2 x 2.4Ghz, 16GB RAM, GTX 660
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5 Replies
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Most devices can’t handle the bandwidth (or is it the frequency?) of HD video. If it’s working (It shouldn’t though) then you’re good. I wouldn’t think you are doing any damage though.
Chuck
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Thanks for the reply. Yeah its not even a device really. Like i’m imagining inside a RCA switch is just a physical switch moving (physically) between one pair of contacts and another. So that kinda makes sense to me why it would work.
Mac Pro 2 x 2.4Ghz, 16GB RAM, GTX 660
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Curious as to whether Bob Zelin could shed any light on this? He seems pretty knowledgable on HD SDI. The switch being probably under 3cm’s in wiring and being originally designed for composite (which uses RCA or BNC connectors), would that degrade the signal? Or will the 1.5-3ghz signal survive completely unscathed going through it?
Heres the switch i’m looking at:
Mac Pro 2 x 2.4Ghz, 16GB RAM, GTX 660
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Would it work as a switch? Probably. Is it the right way to do it? Nope. While it might work for short distances, the cables you are probably using aren’t designed to carry a high definition signal and the two signals will not be in time with each other when you throw the switch. It will cause a big glitch when you switch between your sources. If you are feeding a monitor or a projection system, it will look bad but do no harm. If you are feeding a recorder or digitizing it into a computer, you can cause yourself a whole world of hurt with a bad recording or a corrupt file. Since it’s just a mechanical switch, it will pass the signal, but it’s not designed to carry the kind of signal you are sending through it. Proceed at your own risk.
E=MC2+/-2db
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I am using Coax 75 ohm cable (R151), with maximum lengths of about 2-3m so i’m assuming i’m ok in terms of the cable. Its certainly been passing HD signals from my camera to external monitor all this time.
I am using this switch to feed into a live streaming device. Basically its accepting whatever feed it gets and encoding it into a live stream acceptable to Akami. If I do a physical patch between the 2 sources the live streamer doesnt glitch or anything. It just picks up that the source is now a different format (i.e 1080p to 720p) and continues converting that source to its designated output.
There is a green flash when the patch is made, but i’m not concerned about that as its only very brief.
So I was just trying to replace the physical patch with a switch device that makes the switch over a little quicker, but without any quality loss.
Anyway, i’ve bought the switch so when it comes i’ll post up how it goes.
Mac Pro 2 x 2.4Ghz, 16GB RAM, GTX 660
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