CATx Cables

Overview

CATx is a term often used when referring generally to a Network cable which will actually be of a more particular type or Category. This page is here to give some insight into what the different Categories of cable are, and which one is best for your requirement. CATx cable has a long heritage right back to Category 1 cable, introduced in 1985.

For the purpose of this page, we will concentrate on "Modern" CATx, Category 5 and above only. (there's a wealth of information online for those interested in CAT 1 to 4).

Construct

Modern CATx cable is made up of 8 individual insulated cores (wires) contained within a single outer sleeve or jacket. These wires are grouped in 4 pairs and colour coded for visual matching end to end.

CATx cables are terminated at either an RJ45 plug, or at a Punchdown block in a socket or patch panel. Termination conforms to the telecommunications standard standard "ANSI/TIA-568" or T568. T568 has an A and a B pinout, this stems back from the days when connecting two "intelligent" systems together would require a crossover in the pinout, to connect Transmit to Receive and Vice versa. Today's systems are capable of automatically negotiation the crossover and the A variant of the pinout is rarely used outside certain applications. T568B is how most cables are now terminated at both ends.

 CATx cable construction.             RJ45 Plug terminated.  CATx Punchdown.       T568B pin out

 

CATx Why so many Categories?

The 4 pairs in CATx cables are twisted together. This twisting lends itself to preventing the signals from interfering with each other as they travel along the wire. Through the iterations of CATx cables there have been improvements made to the twist ratios resulting in increased bandwidth and in turn greater data transfer rates being possible. The table below demonstrates the different cables and their capabilities.

Category	Bandwidth	Throughput	Max distance
CAT5	100MHz	100Mbps	100m
CAT5e	100MHz	1Gbps	100m
CAT6	>250MHz	1Gbps	100m
CAT6a	500MHz	10Gbps	100m
CAT7	600MHz	10Gbps	100m
CAT8	1600 - 2000Mhz	25 - 40Gbps	30m

Shielding/Screening

Shielding or Screening is another variation between CATx cables. While as mentioned, the twist ratio* differences between the 4 wire pairs, offers substantially a reduction in how much the signals can interfere with each other whilst they travel along the cable, External sources of EMI "ElectroMagnetic Inteference" can negatively impact the signals from outside the cable. There are a great many potential sources for EMI; Man-made such as power cables, door sensors, PMR radios etc.; As well as natural sources such as Lightening strikes, ESD and switching circuits. A strong enough interferer can cause havoc to the desired signal in your wire. Cable screening is a way to reduce/prevent this interference, or at the very least reduce it to a negligible level. This is the positive aspect of screening. The negative aspect is that shrouding a cable in a foil or braid screen can increase impedance and potentially could inhibit the signal as a result. As a general rule of thumb, for analogue video use unscreened cable and for Digital signals or where interference risk is high, use screened cables.

• the twist ratios in CATx cable can benefit and hinder video signal integrity (see below)

 

Twist ratio variation above, bring the advantage of preventing the Red Green and Blue colour signals from inteferring with each other as their signals are unlikely to intefere with eachother as one a signal wave should never exactly peak high as another exactly peaks low. on the downside, the variation in twist rates results in the overall length of each core being slightly different, resulting in colour Skew as below.

 

So when the colour signal arrive at the receive end of the anaogue extension, the colours arrive at sligtly different times resulting in a blurred image. Many Adder Technology Extenders have mechanisms to apply a skew compensation algorithm to synchronise the arrival of the Red, Green and Blue signals at the display end.

 

Cable breaks/Patch panels

Typically, Cable run installations are broken into sections or "patches", often in order to make rerouting or fault rectification easier, something like the below is not uncommon:

• The patch cable connecting the server to the patch panel is the first point of failure.
• The underfloor cable between the patch panel and the floor box is the second. 
• The patch between the floor box and the desk completes the link.

Each point of interconnection is certain to introduce an amount of loss in the link. that is to say what comes out of the server is reduced in strength by the time it arrives at the Desk.

If an analogue video signal is too weak or contains too much interference, the video cannot be displayed or may be distorted. For Digital signals, the equation is Binary, there will either be enough signal to establish and maintain video, or not. In an environment with an intermittent interference source, the signal may fluctuate on and off as the signal quality rises and falls with the interference. In this case, you may be able to correlate some other event with the problem (e.g. turning on or off a radio, or other device capable of radiating electromagnetic interference).