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Coaxial Cable
1.
2. History:
The real discovery and its actual use dates back to 1929
due to the need for a more efficient and with less
interferences conductor for the transmissions of many
telephone channels on a single "carrier".
Perhaps none of us have never thought that the
development of radio communications would never
have been possible without the invention of coaxial
cable, it is continuously used in our applications that
we don’t think about that.
3. Introduction:
Coaxial cables are the most common, basic transmission
lines.
They are used to transmit electrical energy, or signals,
from one location to another: to connect a source to a load,
such as a transmitter to an antenna.
A coax cable consists of two conductors separated by a
dielectric material.
The center conductor and the outer conductor, are
configured in such a way that they form concentric
cylinders with a common axis. Hence the term and name
co-axial.
5. Construction
The center conductor may be made of various materials and
constructions.
Most common constructions are solid or seven-strand
conductors.
Solid conductors are used in permanent and infrequently
handled applications.
stranded conductors are used in flexible cable applications.
Common materials include copper, tinned or silver plated
copper, copper clad steel and copper clad aluminum.
Plated copper is used to aid in solder ability of connectors or to
minimize corrosion effects.
6. Data is transmitted through the center wire.
The outer braided layer serves as a line to ground.
Both of these conductors are parallel and share the same axis.
That’s is why the wire is called coaxial.
7. Because of a phenomena known as skin-effect, copper clad
materials may be used in higher frequency applications ( > 50
MHz) to improve tensile strength and reduce weight and cost.
Skin-effect is the result of higher frequency signals
propagating along the outermost surface, or skin, of the
conductor.
8. The insulation, or dielectric material, is used to provide
separation between the conductors.
It is desirable that the material has stable electrical
characteristics across a broad frequency range.
9. Temperature range of the cable is often limited by the choice of
jacket material.
The jacket material serves as a protective covering from the
environment.
10. Categories of Coaxial Cable:
Coaxial cables are categorize by Radio Guide (RG).
Each RG number denotes a unique set of
specifications, including:
The gauge of the inner conductor.
The thickness and the type of the inner insulator.
The construction of shield.
The size and type of outer casing.
11.
12. Types of Coaxial Cable:
Flexible coaxial cable:
Flexible coaxial cable is used where the demand is to
fit the cable into a tight space without performance
loss.
13. Semi Rigid Coaxial cable:
Semi rigid cable is using a solid copper outer sheath.
This type of coax offers superior transmission,
especially at higher frequencies.
The major disadvantage of this type is that the cable,
as its name implies, is not very flexible.
14. Hand Formable Coaxial Cable:
These cables are between flexible and semi rigid
cables. These cables are good choices when forming at
a point of installation is required.
15. Twin-axial cable:
Twin-axial cable is a balanced, twisted pair within a
cylindrical shield. It allows a perfect signal which
is shielded and balanced to pass through.
16. Triaxial cable:
Triaxial cable is a coaxial cable with a third layer of
shielding, insulation and sheathing. The outer shield is
grounded and protects the inner shield from
interference from outside sources.
17. Connectors:
The ends of coaxial cables usually terminate with
connectors. Coaxial connectors are designed to
maintain a coaxial form across the connection and
have the same impedance as the attached cable.
Connectors are usually plated with high conductivity
metals such as silver or gold.
In the case of computer networks, BNC (Bayonet Niell-
Concelman) RF connectors are used.
18. Electrical Properties:
The most common electrical property of coaxial cable is
the characteristic impedance. Impedance is the total
opposition to the flow of electrical energy within the cable.
It is a complex value defined by the cable’s resistance and
capacitance. It is expressed in Ohms. A simple formula to
determine the impedance of a coaxial cable is:
Impedance= 138*Vp*log10(D/d)
Vp= Velocity of Propagation(is the speed at which a signal
travels through the cable with respect to the speed of light.)
D = Diameter of the Dielectric
d = Diameter of the Conductor
19. Capacitance:
Capacitance is the ability of the cable to hold a charge.
The larger the capacitance value, the longer it takes a
signal to reach full amplitude within the cable.
Therefore, higher capacitance is usually a bad
attribute.
20. Physical Properties:
Temperature Rating:
Temperature Ratings provides the limitations on
temperature extremes that the cable material can
handle. The safe range is based upon the thermal
properties of the dielectric and jacket materials that
assures that the product will not fracture or melt.
Pulling Tension:
It is typically a safe value well below the break strength
of the cable. Staying below this maximum assures that
the conductor will not be stretched in the cable.
21. Attenuation:
Reduction of signal strength during transmission.
It is dependent upon the cable design and is both
frequency and length dependent. It increases with the
increase in frequency.
It is most effected by DC resistance of the center
conductor and dissipation factor of the dielectric
material.
Attenuation is measured in decibels.
23. Repeaters:
Repeaters are used in coaxial cables to reduce
attenuation.
A repeater can couple together two 500m segments of
coaxial cable. The repeater occupies one transceiver on
each segment and must pass all the signals from one
cable to other.
24. Reflection losses:
Reflection losses are based upon signals reflecting back to
the source rather than propagating through the cable.
These reflections are caused by impedance mismatches or
variations in the cable.
Randomly spaced throughout the cable, these mismatches
will cause minimal loss, but when spaced periodically, that
is at the same repeat distance, they add up together causing
a large loss corresponding to that period wavelength.
This loss can be minimized by quality cable manufacturing
techniques and proper installation practices.
25. Cross Talk:
Crosstalk refers to the amount of coupling
between adjacent wire pairs, which occurs when a
wire absorbs signals from adjacent wires.
Crosstalk is measured by injecting a signal into
one pair and then measuring the strength of that
signal on each of the other pairs in the cable.
27. Applications:
Long distance coaxial cable was used to connect radio
networks and television networks.
It is used by consumers to connect television receivers
to external antennas. Short coaxial cables are also
employed to connect home video equipment and radio
systems.
Micro coaxial cables are used in a range of consumer
devices, military equipment, and also in ultra-sound
scanning equipment.
Coaxial cable are also widely used in local area
networks(LANs).
28. Benefit:
The main benefit of using a coaxial cable is that it is
the default cable of its type. This means that most
electronics is already compatible with coaxial.
Other benefits of the coaxial cable include its ability to
shield television from outside interference. This can
maximize picture quality and help to avoid static.
It is inexpensive also.
29. Advantages of Coaxial Cable:
They are most common means of data transmission
over short distances.
They are cheap to make
Cheap to install
Easy to modify
Good bandwidth
Great channel capacity
30. Disadvantages of Coaxial Cable:
Signals entering the cables can cause unwanted noise
and picture ghosting, making it useless.
A continuous current flow, even if small, along the
imperfect shield of a coaxial cable can cause visible
and audible interference.
More expensive than twisted pairs and is not
supported for some network standards.
It is also has high attenuation, have the need to
implement repeaters.
