Coaxial cable is usable?

Hello,

Is it possible to use a short 2 meters coaxial cable in order to connect a HD-SDI camera into a BlackMagic board? I have tried to use such cable but I cannot see any image been captured while using the Blackmagic Media Express application. The camera manufactured said I should use SDI cable instead of a coaxial one. But I have found some references that I could use a short coaxial cable in a SDI application.

Thank you!
Andre

Hi Andre!
An SDI cable is really just a 75ohm coaxial cable. Having the right impedance and good connectors is important. Even for short ranges. SDI is a high bandwidth signal (several GHz!) so you need a good cable and connectors to avoid reflections and standing waves. In general, your average analog video cable will not work well for SDI. A high quality RG-59 cable with matching connectors should work fine.

OK! Thank you!
Andre

I use good (!) old green coaxial cables up to 50m for 1080i connections to ATEM TVS.....

An SDI cable IS a coax cable. A coax is any round cable with a single center conductor, a shield on the outside, and an insulator in between. In some, that insulator is an air gap. I've worked with coax "cables" used in TV and radio transmission towers that are made of 5 inch diameter rigid copper pipe on the outside, with another small rigid copper pipe on the inside, and nothing but air between. It is still considered a coax.

But not all coax are created equal, and they have different impedance properties. Although damned near any coax should work in a distance of 2 meters, certainly if it is a 75 ohm coax.

Often when newbie people use the term "coax", they mean the type used for Cable TV in the home. Those are 75 ohm, but use an F connector instead of the BNC connector used in SDI. An F to BNC adapter would do the trick, but a new coax with BNCs on it probably costs less than the adapters.

AND, FYI, I just tested out a short 2 meter cheapo RCA cable (one of those red and white audio cables that come free with consumer equipment - also considered a coax - though of extremely poor quality and design) with some adapters and it passed 1080i HDSDI just fine at that short distance. I know it isn't actually a 75 ohm coax, and that RCA connectors aren't 75 ohm either.