Coaxial Cable

Hello friends. today we are going to see the another Common transmission medium the coaxial cable. Coaxial cable, commonly called as coax is a type of copper cable. It has better shielding than twisted pairs. 

Structure of Coaxial Cable

Coaxial cable consists of a stiff copper wire surrounded by an insulating material. The insulator is encased by a braided mesh cylindrical conductor. The outer conductor is covered in a protective plastic sheath. Coaxial cable gives a good combination of high bandwidth and excellent noise immunity. The bandwidth is depends on cable length. E.g. 1km cables, data rate of 1 to 2 Gbps.

This cable is commonly used in telephone system, cable television and some LAN.

coaxial Cable

Types of Coaxial cable

Coaxial cable is commonly used in two types depending on their impedance and ohms. Impedance is the amount of resistance the waves proceeding through the coaxial cable. The lower the impedance, the more easily the waves flow through the cable. Standard coax impedances are 50-75 ohms. This has been tasted as a great balance between power handling a low loss. These  two types are as follows.

Baseband coaxial cable

50-ohm cable, called baseband coaxial cable, is commonly used for digital transmission. It transmit a single signal at a time with very high speed. The transmission of digital signal on the cable is bidirectional. For 1Km distance, baseband cables bandwidth is 1-2 Gbps but for longer distance, cable can used with low data rates or use amplifier to increase the power of signals.

Broadband coaxial cable

Another 75-ohm cable, called broadband coaxial cable, is commonly used for analog transmission on standard cable television cabling.

Broadband networks (a) Dual cable, (b) Single cable.

Broadband systems typically cover a large area and therefore need analog amplifiers to strengthen the signal. These amplifiers can only transmit signals in one direction, so a computer outputting a packet will not be able to reach computers upstream from it if an amplifier lies between them. To solve this problem, two types of broadband systems have been developed: Dual cable and single cable systems.
Dual cable systems have two identical cables running in parallel. The root of the cable tree is head-end. All computers transmit data on cable 1 and receive data on cable 2.
Single cable system allocates different frequency bands for inbound and outbound communication on a single cable. The low frequency band is used for communication from the computers to the head-end, which then shifts the signal to the high-frequency band and rebroadcast it. for inbound traffic, 5 to 30 MHz frequencies are used, and for outbound traffic, 40 to 300 MHz frequencies are used.

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