Twisted Pair Cables Characteristics and it’s Applications in the Physical Layer

In the previous post, we have seen the construction and applications of the Coaxial cables used in the physical layer. Now in this post, we will explore the basic details about the twisted pair cables characteristics and its various applications. 

The construction of twisted pair cable is as shown in the below figure. This is a very commonly used medium and it is cheaper than the coaxial cable or optical fiber cable . 

A twisted pair basically consists of the two conductors (normally copper), each with its own plastic insulation, twisted together.

One of these wires is further used to carry signals to the receiver, and the other is used only as a ground reference. The receiver uses the difference between the two. 

Twisted pair cable is a type of wire in which the two conductors of a single circuit are twisted together for the purpose of canceling out the electromagnetic interference from the external sources. 

Types Of Twisted-Pair Cables  !!

The two commonly used types of twisted pair cables are as follows:

1. Unshielded twisted pair (UTP)       

2. Shielded twisted pair (STP)

The construction of UTP and STP cables as shown above . 

Shielded twisted pair 

STP cable has a metal foil or braided mesh covering that mainly encases each pair of insulated conductors. Although metal casing improves the quality of the cable by preventing the penetration of noise or the crosstalk , it is bulkier and more expensive.

This is known as the metal shield which is normally connected to ground so as to reduce the interference of the noise. But this makes the cable bulky and expensive. So practically UTP is more used than STP. The STP was developed by IBM and is used primarily for the IBM company only. 

Twisted pairs can also be used for either analog or digital transmission. The bandwidth supported by the wire depends on the thickness of the wire and the distance to be travelled by a signal on it.

Twisted pairs support several megabits/sec for a few kilometers and are less costly .  

Characteristics of STP Of Twisted Pair Cable !!

• The twisted conductors are shielded by a braided mesh to reduce noise interference. 
• Low-cost medium and Support data rates up to several Mbps.

Unshielded Twisted Pair (UTP)

A twisted pair consists of two insulated conductors twisted together in the shape of a spiral as shown in figure . It can be shielded or unshielded. The unshielded twisted pair cables are generally very cheap and easy to install. But they are badly affected by electromagnetic noise interference.

In a balanced pair operation, the two wires carry equal and opposite signals and the destination detects the differences between the two . This is known as differential mode transmission.

The cables are typically made with copper wires measured at 22 or 24 AWG (American wire guage) with the coloured insulation. 

Twisting of wires will reduce the effect of noise or external interference. The induced emf into the two wires due to the interference tends to cancel each other due to twisting. The number of twists per unit length will then determine the quality of cable. More twists thus mean better quality.

Characteristics Of Unshielded Twisted Pair (UTP)

1. These cables ensure less crosstalk and a higher quality of signal over longer distances. Therefore these cables are popularly used for high-speed computer communication.

2. The wires are not shielded and can support a data rate of several Mbps.

3. Used in applications like analog and digital telephony i.e LAN etc 

4. Noise and electromagnetic interference are high.

Connectors used with the twisted pair cables 

For connecting one computer to the other, we need to use some transmission medium such as a cable. For connecting these cables between two computers we have to use connectors on both ends of a cable.

The Unshielded Twisted Pair (UTP) cable is the most commonly used cable in computer communication. RJ45 is the most commonly used UTP where RJ is the short form of Registered Jack. It is a male-female type keyed connector.                                                                                                                                       

Applications of Twisted Pair Cables                                        24 awg twisted pair shielded cable

UTP cables are found in many ethernet network , telephone system , security camera system . Twisted-pair cables are used in the telephone lines to provide voice and data channels. 

The DSL lines that are used by the telephone companies in order to provide high-data-rate connections also use the high-bandwidth capability of the unshielded twisted-pair cables.

In the next post, we will further look into the detailed working and applications of the optical fiber cables . So stay tuned..