Computersight -

Copper Cables

Let’s start with copper-based cables since they are the most common and the easiest to install. This is particularly true when making custom cable runs. Before I discuss the types of copper cable that are readily obtainable at most hardware or computer shops let us look at the categories of cable which you may encounter out there in the wild.

First of all I will start with the oldest types and then progressively discuss the more recent varieties. Please take note that it is highly possible that those just entering into the world of network cabling may not ever actually encounter some of the earlier types of copper cabling other than to remove them.

The reasons as to why this is so will be made clear at the appropriate time. For now though you can safely assume that being made of a considerably thick copper core does give the early coaxial cable scrap metal value.

Coaxial Cable

Coaxial cabling consists of a single central copper conductor core surrounded by a foam filler layer. Both layers are surrounded by a braided metal shield and then by another outer covering sheath usually plastic.

The inner foam layer; which is fire resistant, was also intended to provide insulation between the center conductor and the braided metal shield which acts to reduce (even block) any outside EMI from fluorescent lights, motors, and other computers. It also helps to make coaxial cable tear resistant which as you will soon learn has both an upside and a down-side.

The final layer; usually composed of some waterproof material such as plastic is there for overall protection and to provide resistance to environmental damage such as that which water might cause.

Coaxial cabling is notorious for being difficult to install but it is highly resistant to signal interference and can support greater cable lengths between network devices than twisted pair cable (STP & UTP). One of the reasons for its difficult to install nature is due to the outer braided metal layer and the overall thickness in diameter of both the inner conducting signal carrying layer and the overall thickness of the entire cable as a package.

Types of Coaxial Cable

There are two types of coaxial cabling; with each being named for reasons that will soon become obvious:

1. Thick Coaxial Cable

• Thicknet – Also referred to as thicknet and was the first variant to be used with Ethernetnetworks
• Thick Coaxial Cable has an extra protective plastic cover to assist in resistance (tolerating) to damp/humid environment tolerance by keeping moisture away from the center conductor. It is this extra layer that makes thick coaxial cable thicker than thin coaxial cable and hence the name.
• Ethernet – When carrying Ethernet signals the term 10Base5 is used to describe the specifications to which the cable must adhere in order to be suitable
• Ten – The 10 refers to the cable’s maximum data throughput of up to 10 Megabits/sec
• Base – The BASE tells us that this cable is intended for use with baseband signaling as opposed to broadband signaling.
• Baseband signaling means signals and/or systems whose range of frequencies is measured from zero to a maximum bandwidth or highest signal frequency. Generally the entire spectrum range is used with every transmission. This meant that only one signal could be propagate across the medium at a time.
• Five – The 5 refers to the maximum segment length being 461.5 meters (approximately 1600 feet or 500 yards)
• Linear – In addition 10BASE5 cables had to be one linear run
• Terminators – Another requirement was that 50 ohm resistive terminators had to be installed at both ends of a cable run
• Transceivers – For 10BASE5 networks transceivers had to be installed at 2.5 meters. This was so as that reflections from multiple taps were not in phase which helped in reducing the amount of noise and signal degradation. Suitable attacment locations were marked on the cable.
• N Connectors – Transceivers could also be connected by using N connectors at the end of a cable segment
• T-Connectors – T-Connectors are not allowed
• Attachment Unit Interface (AUI) – Transceivers are connected to nodes via an interface that was known as the Attachment Unit Interface (AUI) which is a 15-pin, double row D-Sub type of connectort that used clips rather than screws for cable resistance (to stop the cable from being accidently dislodged)
• 10BASE5 coaxial cable is rather stiff and measured approximately 9.5 mm (0.375 inches) in diameter with an impedance of 50 ohms
• 100 Nodes – A 10BASE5 network segment can support up to 100 nodes
• Thick coaxial cable was a great choice when running longer lengths in a linear bus network compared to 10BASE2 (thin coaxial cable)
• Non-Flexible – Thick Coaxial Cable’s greatest disadvantage is that it is very difficult to install because of its thickness and lack of flexibility

1. Thin Coaxial Cable

• Thinnet – Also referred to as thinnet. When carrying Ethernet signals the term 10Base2 is often used
• Ten – The 10 means that the cable was rated at a maximum data throughput rate of 10 Megabits/sec
• BASE – The BASE tells us that this cable is intended for use with baseband signaling as opposed to broadband signaling. Baseband signaling means signals and/or systems whose range of frequencies is measured from zero to a maximum bandwidth or highest signal frequency. Generally the entire spectrum range is used with every transmission. This meant that only one signal could be propagate across the medium at a time.
• Two – The 2 refers to the approximate maximum segment length of 200 yards (185 meters)
• Thin Coaxial Cable – Was very popular in school networks, especially linear bus networks
• Termination – Another factor that needs to be taken into consideration when working with coaxial cabling of all varieties is the need to terminate any cable segments that were not fixed to another device.
• T-Connectors – When wiring a 10BASE2 network, special care has to be taken to ensure that cables are properly connected to all T-connectors and appropriate terminators are installed.
• Installation Unfriendly – Although; easier to work with and install than thick coaxial cable it was still cumbersome and difficult to work with



• Comparative Improved Flexibility – This state of affairs was due in part to the solid copper core and its relatively thick diameter and the outer mesh metal layer. You may have used Bar-B-Que gas bottles that used hoses that had an outer metal mesh layer and will therefore have encounter this problem before. 10BASE2 was more flexible than 10BASE5 but it was still a problem.
• Single Point of Failure – A failure at any point of the network cabling tends to prevent all communications which made 10BASE2 difficult and time consuming to administer, manage, maintain and troubleshoot.
• 10BASE2 Implementation – The characteristics of 10BASE2 and thin coaxial cable meant that it was ideal for small networks of 2-4 machines.
• Competition – The main reason that we never saw wholesale rollout of 10BASE2 was that CAT 3 cable and the forthcoming CAT 5 cable were considerably cheaper and easier to install were being to build up a head of steam in terms of sales and general acceptance. As a result 10BASE2 was never really main-stream consumer first choice for use as a network medium. However; Its academic installation base did mean that it hung around for a long time.

Coaxial Cable Connectors

The BNC connector is the most common type of connector to be found in association with coaxial cabling. BNC – Bayone-Neill-Concelman or bayonet connector.

There are also other types of connectors and adapters that have been used in networks that were using thin coax as their medium including: a T-connector, barrel connector, and terminator.

Crimp

As always it is the connectors on the cable that are the weakest points in any network and coaxial connectors are no exception. It is therefore particularly important to use coaxial BNC connectors that crimp rather than screw onto the cable as they consistently produce stronger and more reliable connectivity.

Vampire Tap

One of the major advantages of 10BASE5 cable was that it allowed for new connections to be made while all existing connections remained live (still in use). The device used to do this is called a vampire tap.

With practice the cabler was able to clamp the vampire tap onto the existing cable by forcing a spike inside the tap to pierce through the outer shielding layers to make contact with the solid copper core that performed the transmission and reception of the signal.

Other spikes; which bit into the outer conductor, were deployed at the same time as the copper core was being spiked when a special tool clamping/crimping tool was used to perform the clamping procedure. These clamps/crimps were readily available from hardware stores, electronics stores and electrical supplies stores.

It was not long before we began to see vampire taps built into the transciever because this allowed the use of more flexible multi-wire cables

Repeaters – Repeaters are used in scenarios where there is a greater distance between machines than the manufacturer’s cable specifications cite as being the maximum distance that this particular copper cable could be run if you hope to get any worthwhile service. In order to increase the maximum distance between nodes that the manufacturer’s specifications stipulated as being so repeaters can be used.

In the next article we will be continuing our investigation of network cabling using copper-based cables by having a look at twisted pair cabling starting with shielded Twisted Pair (STP) and Unshielded Twisted Pair (UTP)