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VGA/BNC video chaos


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Hi All


I need someone with a better video head than mine to try and solve a problem. Here is the setup from source to end.


1x Macbook with Mini display port.

1x Macbook with Thunderbolt

Both have Mac-VGA adapters - Output 800x600 60hz


2x VGA cables into an Octo-fade switcher

Octo-fade output set to SOG

Input and output as above


VGA to BNC cable out (similar to this)


Connecting to a BNC amp


7x BNC lines out to 7 monitors. The screen output I get on all the screens is of the mac desktop, in three bars, three times, B&W, flickering.



It's driving me nuts and becoming an issue for the show, I have checked all the VGA cables W/dongles separately (Mac to monitor), camera into BNC amp and VGA out from the Octo-fine. The weak link seems to be either the VGA-BNC cable, that the Mac's are outputting at 60HZ or somthing else.

Does anyone have a clue ;)


Thanks in advance.

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Yorkie - It is a Extron video distribution amp 1 BNC in 12 out, 5 monitors and 2 plasmas using video in.



TonyMitchel - Just done some digging and pulled this out.




I know very little about video but guessing this is not good.

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Have you tried changing the resolution? What monitors are you plugging into? It may be that they only expect to see 576i PAL and you are trying to give them a data res at 60hz. Some picture of the setup will help.


Yep tried various output res but no joy. they are standard LCD monitors, will try and get some pictures.


setup in images:

Mac output


Octofade input/output


Octofade settings



VGA-BNC output


BNC amp



Plasma rear


Monitor rear


Final output




I have also bypassed the BNC amp and hooked the VGA-BNC cable direct to a monitor.

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I don't know anything about the octofade or the amp but it sounds a lot to me like you are trying to get composite video from one leg of a vga signal (vga is basically a video signal split in to Red Green Blue and syncronisation - more to it but that's roughly the jist) so you will never get a decent display on your plasma.


You'll either need convertors to change from vga to composite video (the cable you show will not do it) or do all the switching and distribution at vga level - sorry I don't know much about kit that can do that...


It's worth pointing out that there isn't a BNC amp as such - BNC is the type of connector used. It can carry several different types of signal, from simple composite video (as a VHS player would spit out) or VGA (as with the cable you show), it can also carry RGB (think SCART) and also RF (i.e. radio signals).

The amp you have just has BNC as it's type of connector, it could be amplifying any of the signal types I have mentioned.


If you could say exactly what you are trying to achieve and the kit you have, hopefully someone (with more knowledge than me!) will be able to talk you through what cables and any extra kit you may need and how to make it all work nicely. :)


Based on what you've already said, it sounds like the amp is the issue, you need a vga amp (i.e. has the 15pin connectors) instead.

Something a bit like this.

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OK, your Plasma and monitor have VGA in so as Sleah says, that would be the best solution in the analogue world - VGA out of Octo Fade and VGA distribution amp to all monitors. Better quality signal compared to composite.


If you have to go down the composite route you will have to scan convert the signal as (now that I have had chance to read the manual - a long time since I used an Octo-fade) its lowest resolution is 800 x 600 in 4:3 so is more than the composite input can deal with. If needs be, somebody may have the good old Sony 1024 scan converter.


You could also go digital as both Plasma and monitors have DVI. Just expect a world if pain with HDCP from the Macs :)


Out of interest, why 4:3 ratio rather than 16:9? Everything will looked stretched on the monitors if you try to fill the whole screen.

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The video signal from your computer is VGA.

The output from your Octofade is VGA.

The input you are using to your distribution amplifier is Composite Video.


VGA and Composite are not the same thing.

The Octofade does not have a Composite video (CV) output.


As suggested by others, if you wish to use the CV inputs on your monitors you would need a scan converter to convert your VGA signal to a composite one.


If all of your monitors/plasmas have VGA inputs, and the cable distances are sensible, I would suggest you obtain a VGA distribution amplifier (DA). With this you could take a VGA cable from your laptop into the VGA DA and connect the outputs of the DA to your monitors/plasmas using VGA cables. Much simpler and the quality of your pictures will be much better!





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