What is the maximum length for SDI video cables?

Answer 1

There is no published maximum lengths for composite or other analog video cables because there are so many factors to take into account. If the driving source is a properly balanced output and the receiver has a properly terminated input and good quality, low loss co-ax cable is used, then the maximum distance can comfortably exceed 100 metres (300ft). However, many domestic video components do not have the best drivers and receivers and therefore, the maximum length will be reduced significantly. With analog signals (composite, S-video, component, RGB) the picture will start to become softer as the cable length increases. Eventually, the image will become unacceptable but it is up to the user to decide what is good enough. In all cases where a long video run is needed, use good quality 75 ohm co-ax cable and within a domestic environment, you should see very few problems.

Answer 2

Standard definition component can run over relatively long distances. The maximum length is dependant on the cable, the source driver and the receiver. Using 75R co-ax cable, 100ft or more should present no problems at all. If the length is significantly more than 100 feet, it will be wise to choose a low loss cable (for low loss, read "more expensive"). With low loss cable, anything up to 500 feet is possible. Some cable suggestions are RG59 for lengths up to 100 feet. For longer lengths, consider a BBC specification known as PSF 1/3.

Answer 3

SDI is the broadcast standard for video links within studios. It is a digital format that can be used for both SD and HD signals. The maximum length of cable depends on a number of factors.

First, the cable quality affects the amount of signal loss over a given length. The better the cable, the longer the cable can be.

Next, the quality of the signal receiver defines the amount of loss that can be tolerated. The better the automatic gain and equalization of the input, the more losses can be handled. Most broadcast equipment use one of a handful of receiver ICs that all perform in a similar way.

Finally, HD signals show far higher losses than SD signals.

As a guide, HD signals can typically handle up to 100 meters (300 feet) while SD signals will often tolerate 300 - 400 meters (1000 - 1200 feet).

When selecting a cable, check the signal losses in the data sheet and use data rates of 270Mbit or 360Mbit per second for SD signals and 1.483Gbit per second for HD signals. The cables will be terminated with BNC connectors. Always make sure that the connector is chosen to suit the cable. There are many connector types and the wrong one will adversely affect the signal quality.

Finally, make sure the minimum cable bend radius is not exceeded. Bending the cable too tightly can also adversely affect the signal quality.

As long as the cables and connectors are chosen correctly, SDI provides a simple and robust link between equipment.