Building a custom cable for a Xenarc 706TSV... impendance question

**Pseudo Nim** · 10-15-2009, 09:43 PM

Hi all,

I need to build a custom cable for a Xenarc 706TSV - the reason being that the stock one won't fit anywhere in my dash. I absolutely MUST use a flat cable.

I got my hands on a pair of male-male connectors (female connectors for this cable, a 20-pin D-sub variation are IMPOSSIBLE to get). So I can't build a short 1ft extension - I _must_ build a whole bloody cable.

Stock cable impedance is around 1.5 Ohms over the ~18ft cable that they provide. My cable is getting around 2.4 Ohms over the 25ft length that I have.

Anybody figure that I would have huge signal loss if I used it? Should I cut it, or is this cable hopeless and I should go shopping for a fancier one?

Thanks for any hints.

-pN

**justchat_1** · 10-15-2009, 09:51 PM

Whats traveling along the cable?

**Pseudo Nim** · 10-15-2009, 10:02 PM

Just the video signal. This is for the cable to go between the monitor and the breakout box (which, in turn, will connect to the PC).

**justchat_1** · 10-15-2009, 10:06 PM

Then yea you should be fine...the bigger issue is to make sure the shielding is ok and that theres no crosstalk

**Pseudo Nim** · 10-15-2009, 10:27 PM

Optimistic about that. The cable is jacketed and shielded with a kind of aluminum foil. Hopefully should be all right.

**Mickz** · 10-15-2009, 11:23 PM

DC resistance (what you measure with a multimeter) is not the cable impedance.

The video and sync cables are usually individually shielded coax and have an impedance of 75 ohm across the video operating frequency, which because of its bandwidth is an RF signal and can be from 15MHz to 100MHz depending on the screen resolution that you are running.

You could use some very small 75 ohm coax for the Video signals and still end up with a relatively flat cable. The other option would be a CAT5 VGA extender which sends the VGA signals over standard 4 pair CAT5 twisted cable.

You could try your way first as you might get away with it over a short length but IMHO you will most likely see some smearing or patterning of the video.

**Pseudo Nim** · 10-15-2009, 11:46 PM

Ahh. I see. Yeah, that's a very good point, I did get the two concepts mixed up.

The question is, though - does this still hold true for digital signal? If I am not mistaken, the connection between the breakout box and the 705TSV is digital (because you can hook up the breakout box over DVI to a PC - and, logically speaking, if the breakout box->monitor was analog, that would sort of defeat the purpose). So with that in mind, are my chances somewhat better?

**Mickz** · 10-16-2009, 12:21 AM

Ok, not having a circuit or information on the interface, this is going to make the answer a little harder.

If they connect the interface box via DVI-D then you could extend them up to around 5m and due to the nature of the signal your cable may work out ok.

There are a few versions of DVI though. DVI-D cables transmit digital T.M.D.S. signals, DVI-A cables transmit analog VGA signals and DVI-I cables can transmit either digital or analog signals.

Sorry can't be of more help, hopefully someone who knows more about this may pop up with a definitive answer.

**Pseudo Nim** · 10-16-2009, 07:15 AM

No, that's no prob, I'm not giving you much info to go on, either

I see what you mean re: length, though. I suppose I don't outright know which DVI they use, but I would _figure_ it's TMDS, seeing as that's what LCD panels typically use, and I don't think they'd go and reinvent the wheel for it. I suppose the best thing I can do is _make_ the cable and see what happens, hehe. Resolder it if I need to, I suppose.

**Pseudo Nim** · 10-24-2009, 12:08 AM

Right... so the custom cable failed. At least try #1. I gave up on trying to make it myself, so I had someone make it. Now, when I plug it in, the screen SENSES that there is a signal, and turns on; then immediately turns off, and a hissing noise comes from the built-in speaker.

Any thoughts on what I should check? I ran a basic check on pins, and all pins SEEM to match up with an ohm-meter. Maybe 28AWG is just simply too thin for a video cable?...