The coaxial cables are widely used cable transmission media. These coaxial cables come in two categories namely: the baseband coaxial cables and the broadband coaxial cables. In this article we focus up on the latter type of the coaxial cables i.e., the broadband coaxial cables.
What are Coaxial Cables?
– Coaxial cables are a type of the guided media used for the carrying the signals lying in the higher frequencies when compared to its twisted pair cabling counterpart.
– Commonly, these wires are known as coax in short form.
– Coaxial cables are available in two types of ratings as mentioned below:
- 50 ohm cable : It is used in the field of digital transmission.
- 75 ohm cable : It is used in the field of analog transmission.
– The coaxial consist of two conductors one over the other lying about the same axis.
– This is why these cables have been named coaxial cables.
– These wires are covered with a shielding.
– It is by virtue of this shielding that the cable is able to provide very high immunity against noise from various sources.
– The coaxial cables can provide a high data rate (up to 10 mbps).
– The data rate of the coaxial cables can be raised further by increasing the diameter of the innermost conductor.
– The maximum number of nodes has been specified as 100 nodes and 30 nodes on thick net segment and thin net segment respectively.
– By now it is clear to that coaxial is nothing but a two conductor cable.
– Here, the outer conductor forms an electromagnetic shield around the inner conductor.
– A layer of insulation provided between the two conductors for the purpose of separation.
– Coaxial cable can be thought of as a transmission cable of constant impedance.
– These cables are fit to be used in both the broadband and baseband transmission.
– Best thing about the coaxial cables is that they do not radiate magnetic and electric fields as well as stay unaffected by them.
– This is what makes fit to be used in transmission even though they are a bit expensive when compared to the twisted pair cables.
About Broadband Coaxial Cable
– The broadband coaxial cables provide a large bandwidth and low losses when compared to the baseband cables and hence the name broadband coaxial cable.
– Furthermore, it is quite easy to install these cables.
– Unlike the baseband cables, the broadband cables have to follow either a star topology or a daisy chain topology.
– In a coaxial cable, a number of small cables are enclosed in a protected cover.
– The purpose of this cover is to provide shielding to these cables from many physical factors as well as from EMI (electromagnetic interference).
– In the addition to this outer covering, the individual cables also have their own shielding to protect them against the interference from one another.
– The use of these cables is widespread in telecommunication networks where many simultaneous communication links are required.
– Broadband coaxial cables can be used without any problem in multi-cast and unicast communications. – In fact, in the local area networks these are the most widely used transmission media.
– Even though being costlier than twisted pair they are less expensive than the fiber optics.
– On a broadband coaxial cable, many different signals can be transmitted simultaneously up on different frequencies.
– Frequencies higher than 4 kHz and therefore is well suited for the analog signals (for this purpose they are used with a modem.).
– Either Manchester coding or the differential Manchester coding is used for encoding the digital signals that are transmitted over these coaxial cables.
– The whole frequency band of the cable is used up during the transmission digital signal.
– This makes the transmission of the multiple channels (via FDM) almost impossible.
– Therefore, the digital signals are transmitted over these cables in a bi–directional way.