Is This Cable Suitable for DMX512 - Page 1
Forum section: electronics / general

author: kolbep
author_rank: Frequent Contributor
timestamp: September 30, 2015, 05:44:58 am
content: Hi AllI have a bunch of this 3 Pair Stranded Screened Cable Lying around.I don't know where it came from..There are no markings on the cable itself, so I cannot get a datasheet for itBasically what I want to know, is how I can find out what the Impedance of this cable is. The DMX Cables ideally need to be about 120 Ohms Impedance. Is there some way I can determine how suitable this would be.I am already using Cat-5 Solid Cable, which works fine (but don't look at it funny, or the wires snap off the XLR Connector). But If I go and put normal 'microphone' cable in for the system, there is a chance the impedance mismatch will cause reflections, etc (as I understand it) and may corrupt the data. That is why I would like to know if this cable of mine is more of an audio cable, or if it could be right for me to use.Thanks

author: Halcyon
author_rank: Unknown
timestamp: September 30, 2015, 06:19:18 am
content: Normally DMX uses standard XLR audio cables. I think due to the low data rate, your cable should be just fine.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 30, 2015, 06:21:37 am
content: DMX is pretty robust - unless your runs are very long, cable isn't too critical.

author: Towger
author_rank: Super Contributor
timestamp: September 30, 2015, 06:22:51 am
content: Any codes printed on it?Maybe intercom/phone cable. It looks like foil screened, is that an unscreened ground in the photo.You can get premade 3 core flex with XLR plugs masquerading as DMX cable on Allieexpress. ..

author: SteveyG
author_rank: Unknown
timestamp: September 30, 2015, 07:47:22 am
content: Quote from: Halcyon on September 30, 2015, 06:19:18 amXLR connectors, yes, but normally DMX512 data cable. Using microphone cables is a real hack and is not reliable.

author: Towger
author_rank: Super Contributor
timestamp: September 30, 2015, 07:56:22 am
content: I have no problems with 'digital audio' cable, which was 100 ohms but has a slightly higher than the dmx spec capadance. Picked up a half used reel on eBay.

author: Halcyon
author_rank: Unknown
timestamp: September 30, 2015, 07:56:40 am
content: Quote from: SteveyG on September 30, 2015, 07:47:22 amI don't know about that. If you have half-decent gear, you'll use decent quality cable for analog audio (which is more than sufficient for DMX signalling). Decent audio cabling is more than enough for reliable performance. Also stick with good quality connectors such as Neutrik. I've used standard audio leads for years (>15 metres long) and have never had dramas. But, always have spare cabling no matter what the application!If you look after your cables, they'll look after you. Avoid sharp kinks, store and wrap them properly (figure-8 with velco ties) and use flexible cabling (the ones with a silicone sheath are really nice).

author: ajb
author_rank: Super Contributor
timestamp: September 30, 2015, 02:38:58 pm
content: Quote from: Halcyon on September 30, 2015, 07:56:40 amThe build quality of the cable isn't typically the concern (at least, not any more than with any other cable), it's the cable's characteristics. DMX specifies an impedance of 120Ohm, analog audio cable is typically lower, sometimes as low as 50, and the impedance mismatch can cause problems in certain situations. That said, it's really only going to be a risk on especially long runs or in otherwise marginal situations, so you can often get away with it with no trouble. I'll admit to having done some pretty ugly DMX wiring in the past, and the only time I've ever seen cabling cause a problem is when there's an actual break in the cable.

author: Towger
author_rank: Super Contributor
timestamp: September 30, 2015, 02:50:08 pm
content: Leaving the terminator off the end is more lightly to cause problems, than using mic cable.

author: kolbep
author_rank: Frequent Contributor
timestamp: October 01, 2015, 06:00:28 am
content: Quote from: Towger on September 30, 2015, 06:22:51 amNo Codes on it. But it is 3 Pair Foil Screened, with the Unscreened Ground with the foil.Well, I have made up a 30m, 20m, and a couple of 6m cables for DMX (Using Blue/Red Pair for the -,+ and using the screen for the gnd connection)Will try it out on the equipment at one of my installations, and see how it goesI do have a terminator on the end of line