Introduction
The demands of extending high-resolution DVI and HDMI digital video signals are considerable and mean that it is not possible to use Cat5e cabling to achieve the maximum extension distance of 50 meters. The large video bandwidth involved means that to achieve the best possible performance from digital extenders, it is vital that the correct cabling is chosen.
There are three important factors to consider when choosing a cable for use with digital extenders.
Note
Types of cable
Twisted pair cables can have either solid or stranded conductors. Solid cables come in bulk spools and are often referred to as infrastructure or bulk cabling. They are less flexible than stranded cables but have less attenuation. These cables are typically run throughout a building and terminate at the rear of a wall plate.
Stranded cabling is found in patch cables and is intended to connect the front of the wall plate to the extender or computer using RJ45 connectors. They need to be more flexible because the cabling gets disconnected and connected constantly.
For a digital extender application, solid conductor cables give a better performance as these allow for higher bandwidth and have less attenuation. Ideally, a thickness of 22 AWG should be used.
Types of RJ45 connector
For each type of cable there is also an associated RJ45 connector. It is important that the correct type of connector is used for the type of cabling.
Insulation displacement RJ45 connectors are designed to work with solid conductor cables while insulation piercing RJ45 connectors are designed to work with stranded conductor cables.
The teeth of the insulation displacement connectors are designed to straddle and hug the sides of the solid center conductor of the cable.
The teeth of the insulation piercing connectors penetrate the middle of the cable and nest in between the stranded wires. If insulation piercing connectors are used on solid core cable then the connection will not be stable as the teeth will try to but are unable to penetrate the solid center conductor. The teeth will then slide off the solid core and not make a stable contact.
Types of shielding
The third and final factor in determining the cable to be used in digital extension is shielding. The shielding protects the cable from two types of interference, internal crosstalk and external interference. Internal crosstalk is the interference between the different pairs inside the cable. External interference is any interference that comes from outside the cable. This is caused by many things; proximity to mobile phones, bundling cables together, or running them over lighting fixtures.
Internal crosstalk is most detrimental to digital extension as the signals cannot be recovered after experiencing crosstalk. You are left with a black screen.
The most common type of shielding is Screened/Unshielded Twisted Pair (S/UTP). This has an overall shield and will protect the signal from external interference. However it does not provide any protection from crosstalk.
The next type of shielding is Shielded Twisted Pair (STP). This has four individual shields, one for each data pair. This is good for protecting the signal from internal crosstalk but does not provide an overall shield to protect against external interference.
If you combine the two types of shielding together you have Screened/Shielded Twisted Pair (S/STP). This is also sometimes referred to as Shielded/Foil Twisted Pair (S/FTP). This has four
individual shields, one for each pair and an overall shield. S/STP is the best cable to protect against any interference and is the cable choice to be used for digital KVM extension.
Adder recommends
We recommend the following two types of cable:
Patch Cables
Daetwyler 7702P flex
This is stocked by Adder with the following part number VSCAT7-50. This is a 50m length of Daetwyler 7702P terminated with HRS TM31P RJ45 connectors.
CU 7702 4P flex
Flexible data cable S/FTP Cat.7 AWG26
Bulk Cables
Daetwyler 7120 with Harting RJ Industrial 10G RJ45 connectors.
CU 7120
Data cable S/FTP Cat.7A AWG 23