Confused about SCART cables. VGA vs Coaxial?

[KoroKoro]

Sorry if this is a stupid question that's probably obvious to everyone / asked a million times before. I've searched, googled and even asked on a few other forums but not getting any answers.

So previously, I have been making my own RGB cables (prior to them being widely available online), so I had converted all of my consoles to output via a 9pin dsub. I then used a VGA cable with one end modified to suit my consoles 9 pin which would then go to my XRGB3s VGA port with a custom audio breakout cable. Unfortunately the VGA cable isn't really suited to carry audio as well. Since I'm hoping to get a gscartsw from the next batch, it seems I will have to redo all my shoddy cabling which is probably all wrong anyway. So not a big problem.

However as soon as I started looking for anything better than what is in the VGA cable, I wasn't able to find anything. I did however find solid multicore coaxial cables designed for high frequency digital... I'm not so sure if this product is appropriate for use with 15~31kHz signals. Then there is Plenum RGB and Riser RGB. Terms I have never even heard of. I've asked on other forums and I'm actually surprised I haven't had any answers.

https://www.anixter.com/en_us/services- ... cable.html



The next part that I am now confused about is resistance, impedance, inductance, capacitance per unit length of cable. I always thought those terms were loosely interchangeable but I think I haven't understood it properly. I don't know how much impedance there is over the length of a VGA cable with the ends chopped off and new connectors soldered on by hand. But the link above states that the cable inherently has a 75 ohm impedance. I would have thought its resistance would be close to 0? Previously I had just added a 75 ohm resistor and 470 uF cap in series. I have tried 220uF but that was actually insufficient. I have now read that I am supposed to have the resistors go to ground instead? I'm sorry but I am completely confused now as to what I'm supposed to do. I have also read that csync needs a 470 ohm resistor to bring TTL level down to video level. I have only been using 75 ohm for a couple of years so I'm worried I have been damaging my XRGB3 this entire time. Is it just me or is there a lot of misinformation out there?


Lastly I have seen that you can get metal SCART connectors with gold plated pins. Would those be worthwhile if I'm now going to use high quality coaxial cable?


Thanks in advance for any help.

Again sorry if these are stupid questions. I'm a bit of an idiot when it comes to these things...

[xAzurexEonx]

Ill touch on a few things.

Wire type doesn't matter unless you are going long distances or using a powered signal.

The additional components needed vary by equipment. Ive seen people needing to use other values on their cables depending on their equipmemt. I cannot speak for this on a xrgb but Id venture to say if it has been working it is fine.

The gold plated scart isnt going to add much if you arent using quailty cable. Its pretty much to have the best components together possible. Its not going to make a vast impovement unless you are using some very low grade sockets.

[citrus3000psi]

Its easy to go nuts on building your own cables. There is lots of cable types out there. I was looking at 6 way van-damme cables

http://www.vdctrading.com/shop/van-damm ... per-metre/

But in the end of the day, retrogamingcables with there packapunch is just sooooo much easier and not much more expensive. Might even be cheaper in the end.

[KoroKoro]

Thanks guys for the responses.

After a bit of googling regarding impedance, I think I've come to the conclusion that solid core vs stranded core is a non issue for these signal frequencies. Though I am no expert, so I could be wrong.

However this has somewhat raised more questions than it has answered. So I understand the cable impedance (AC resistance) is dictated by the sizes / ratios of conductor, insulator and shield diameters... However it is still directly affected by length. However, when it comes to terminations and connector types, I'm still just as confused. So I think I have confirmed that VGA connectors, RCA and BNC connectors are usually of the 75 Ohm flavour... But I have read that BNC connectors are better as they completely shield the conductor, but VGA and SCART connectors have cross talk due to poor shielding.
But I have now read that some designs require a resistor divider right next to the connector then the entire board can be a standard 50 Ohm impedance traces.

So it seems very important to understand what is used on my devices boards and to know exactly what passive components are expected to be in the source console, cable, active switch or destination device (TV/upscaler). Now the fact that the switcher is of an active type, does that mean it is not a direct connection with the source signal, but instead using voltage followers to recreate the signal entirely, thus no direct connection from source to device - meaning I need to attenuate my impedance from the console with trim pots (to adjust for cable length), plus attenuate again on the switch output to the device, again using trim pots?

So would it be wise to bypass my XRGB scart/vga socket with BNC sockets with a direct internal connection to the chip? I fear this would be moot though as inside the device is probably noisy and a direct connection is only possible to the first internal switcher. Not to mention the GscartSW is in the same boat, but with many scart connectors which would be a lot of labour to change over.

I think I am starting to understand a bit more... but I may be going in the completely wrong direction. So if I am talking rubbish, please let me know because I'm only just figuring this out as I go...

Thanks again for the responses.

[gray117]

haha ... oh dear ... honestly don't worry about this.

The short:
For the most part as long as you've not got ungrounded sync strippers or something in your cables I'm sure your xrgb will be fine... being super safe just maybe make sure anything like the megadrive/snes has sync pulled down a bit with a resistor on the sync ... ideally different per console but around 400 ohm iirc ... but I'm sure even these are within xrgb's tolerence...

Bit more detail:
If you're all set on vga cabling keep doing it. Just try (and this is where it's tricky for any bundled cabling scart or otherwise) to use reasonably shielded, well constructed cables. Any video cable will be seeking to hit around 75ohm impedence... reasonable (no need to go over the top) is the main thing. You'll be wary of especially around bundles of other wires/chunks of metal/lots of power cables. But 95% of the time if you've got rubblish shielding you'll just see it immediately without these other things making it worse. A good way of testing a vga cable in particular is to use it on a regular lcd monitor and computer, set to native resolution, auto adjust the screen, and look for any inconsistencies or blurring/doubling shadowing of the image ... try coiling/ bending the cable, putting it down with a bunch of othered powered decvices and make sure nothing happens.

Component (such as maybe seen in pro monitors) cabling where each line is it's own wire is often an good way to super shield/troubleshoot issues... but tbh it's over the top - especially if you're already good to go vga wise. You could use single coax or bundled coax to do something similar if you really wanted.

Scart/vga/bnc ... it's just a plug, with wires connected to pins ... nothing more or less. vga is both compact and sturdy and probably the best single one. But convenience is kind of king


Now for the whys:
Impedence is not just resistance 75 ohm video cabling is what you want.

TLDR, just read this:
http://www.l-com.com/what-is-the-differ ... ne-be-used

...

The explanation:
http://www.physlink.com/education/askexperts/ae517.cfm

How this relates to cables:
http://cablesondemandblog.com/wordpress ... ial-cable/

[mvsfan]

Mini Coaxial is the best. IT has the least interference. But what also works, Is just to run your audio in a seperate wire, going from your console plug to the video connector.

if you run audio and video in seperate cables it usually solves any interference issues between audio and RGB, and is a whole lot cheaper than coaxial.

a lot of the other stuff is minimal. i wouldnt worry too much about it.

Csync is the best form of sync. Use it if you can. If your console doesnt output Csync, like the PS1, you can also use Sync on luma wich is also good.

As far as your cables go, I just started using a new setup,(for me). Custom console cables with a VGA Connector, and phoenix connectors for audio, So i can hook all my consoles to an Extron MVX. Vga connectors are much better than scart. they dont fall out of the socket for one. And no loose connections. Not getting the rather frequent missing Red, Green, or Blue because a scart cable came loose again, made it well worth it to me.

[numbski]

This reminds me - KabelDirekt cables on Amazon actually appear to use decent quality conductors, but they're hooked up all wrong. As a result, the audio channels aren't shielded and buzz. If you switch it around and make sure to ground tie the shielding, they are glorious.


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