# Calculate coaxial cable type/grade to transfer digital video signals to a known distance/length

To transfer digital video signals to a known distance/length, like "L", I need to calculate which type/grade of coaxial cable I need to implement.

I was wondering what is the industry/best practice for doing such calculations. Thanks.

## 1 Answer

Major cable suppliers such as Belden and GEPCO publish guides that correlate at least two factors:

1. Signal bandwidth or SMPTE standard (standard def, HD, 3G, etc)
2. Cable length

There are three other factors that make a difference: the quality of the connectors, the quality of the physical installation of the connectors on the cables, and the quality of the signal drivers (distribution amplifiers).

One industry best practice is to use the conservative numbers published in the guide, using only the best-quality connectors matched with the cable type in question. The cheapest and/or lightest and/or smallest diameter cable is then selected from the available options.

Another best practice is to use the "up to" numbers published in the guide and then measure whether or not the level of signal loss is acceptable for the given connectors, drivers, and receivers of your actual devices, using the cheapest, lightest, and/or smallest diameter cable that appears feasible. This can be done before actual installation of the cable, but not before acquiring all the relevant video sources and sinks, and not before actually cutting a maximal length of cable(s) to test it.

Cable manufacturers publish their specifications. Steve Lampen explains about Belden does their calculations and what happens as you approach the high end of the cables maximum length. Best to use those specs for your calculations, not some random number that you find on wikipedia for a "generic" cable.

• Pick two, maybe three, different cable "families" to use. Many US projects use Belden 1694A for anything between racks and 1855A within a rack. If you need a plenum cable, use 1695A, not one of the other plenum rated cables. This will keep your connector stock and tooling to a manageable size. Don't try to pick the "best" cable from all of the Belden cables on a cable by cable basis. Definitely don't use the Belden or Gepco lengths for a generic cable. If you are building a permanent facility, it is well worth it to spend the money on high quality cable and connectors. May 31, 2017 at 0:36