Communication Cables
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History of Cables:
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The earliest use of cables was in Telegraphy lines. The cables were termed as SWER
(Single Wire Earth Return) circuits, Figure 3. These are single phase lines (uninsulated), that were used in Single Wire Transmission. The use of this form of
communication soon started having interference (noise) from the Trams (Electric
Trains) and other electricity-using devices.
After this, companies converted to Balanced circuits lines. These are implemented
using two wires which have circuits installed at every distance, or at the receiving
or transmitting end, that cancel out the interference. See figures 5,6, and 7.
– Secondly, since the they are two wires, on transmitting and the other
receiving, the interference in the two lines is canceled out automatically.
– Balanced lines increase length by decreasing the signal attenuation.
Since most of the telephone lines were installed next to power lines, this caused
the interference that is induced from the power lines, and with the advancement
of power, the interference kept on increasing.
This brought in a new era of the wire transposition, Figure 4 in a bid to reduce on
the interference induced into the cables. In wire transposition, the transmit and
receive cables change position every 6 to 7 poles (around 4 twists every
Kilometer). The change in position helps to increase interference cancelation.
The wire transposition was not enough in the reduction of noise in the
communication lines. This led to the introduction of twisted pair cables.
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Figure 3- SWER
Figure 6- Balancing with
capacitor and inductors
Figure 4- Wire
Transposition
Figure 5- Balancing with
Transformers
Figure 7- Balancing with
Op Amps
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Fig. 1. Balanced line in twisted pair format. This line is intended for use with 2wire circuits.
Fig. 2. Balanced line in star quad format. This line is
intended for use with 4-wire circuits or two 2-wire circuits.
It is also used with microphone signals in professional
radio.
Fig. 3. Balanced line in DM quad format. This line
is intended for use with 4-wire circuits or two 2-wire
circuits.
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Fig. 4. Balanced line in twin lead format. This line is intended for use with RF circuits,
particularly antennas.
The twisted pair cables aim at cancelling EMI (Electromagnetic Interference) from all
neighboring cables.
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Computer Networking History:
10BASE5
The earliest form networking was done by coaxial cables, implementing 10Mbps
using the RG-8X type (expensive) of coaxial cable. To add a computer to the
network was simple as drilling into the cable to its core and connecting a coaxial
cable to the core.
10BASE2
In the next generation of networking, a 50Ω RG-58 coaxial cable (cheap) was used.
This remained a dominant networking method for a long, with a network speed of
10Mbps. To connect another computer to the network, a T-connector BNC was
used.
1BASE5
Then came first use of the twisted pair but accomplishing connection speeds of
1Mbps, with a hub. This kind of networking never went commercial.
10BASE-T
The next generation was the 10Base-T which was running over four wires (2
twisted pairs) on a Category 3 or 5. An active hub or switch sits in the centre of the
network and has a port for each node. This is same configuration that was used in
the 100Base-T.
FOIRL
The next generation is the fiber-optic inter-repeater link (FOIRL). This is the original
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standard for Ethernet over fiber.
Cable Overview – Based on Applications.
1.E1
2.Ethernet (Cat 5, 5e and 6)
3.Coaxial Cables (un-balanced line)
4.Fiber
5.Waveguide
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E1/ T1 Cables:
Figure 1:
The cable shown in the figure is an 8E1 cable.
Depending on the Size of the Cable, it can carry from 8 to 32 E1s/T1s, each E1
being made up of 4 twisted cables. Each pair of cables is twisted onto each other
to achieve noise cancellation. The cable shown in figure 1 is a Cisco Cable. For
more information of how its used, read thru the mvcbl.pdf.
Please note that E1s can also be achieved using the an RJ 45 Connector, as
shown in figure 2. The figure shows the implementation of 2 E1 using Cat 5 cable
and RJ 45 Connectors.
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Figure 2:
Ethernet Cables:
These are the cables that are mainly used in computer networking, in LANs
(Local Area Networks).
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Ethernet Cables (3, 5, and 6)
Introduction:
Ethernet cables are used mainly in LANs. It should be noted that in all these
cables, the same kind of connector is used, RJ45. Its the type of cable that differs.
Cat 3:
Commonly known as Category 3, is a UTP (Unshielded twisted pair), designed to
reliably carry 10Mbps at the bandwidth 16MHz. This type of cable was common in
the early 1990s’, but its popularity fell to a more faster and more reliable cable, Cat
5.
Cat 5:
Category 5 is a twisted pair cable with a high signal integrity. Its designed to be
used in both Ethernet and ATM applications. Its also used to carry other types of
information, ie Telephony and video. Most the Cat 5 cables are unshielded relying
to the twisted nature for noise rejection. Mainly used for 100Mbps.To view the
other specs for 5, 5e, and 6, please look thru the document specs.pdf.
Cat 6:
Also known as category 6, its mainly used for Gigabit Ethernet and is also
compatible to cat 3, 5, 5e. For more details, please look thru the document
specs.pdf.
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Coaxial Cables:
Coaxial cables provide the simplest and most versatile method for transmission of
RF and microwave energy. The common types consist of a cylindrical metallic inner
conductor surrounded by a dielectric material and then enclosed by a cylindrical
metallic outer conductor. The dielectric material is used to maintain the inner
conductor concentrically within the outer conductor. The dielectric material is
typically polyethylene (PE), Polyproplene (PP) or tetraflouroethylene (TFE). Most
coaxial cables are then coated with a protective jacket made of polyethylene or
poly-vinyl chloride (PVC).
General Applications:
Short interconnections between RF electronic equipment
Usually this application is inside buildings, and in equipment racks, these cables,
traditionally, have been called RF cables. They are usually 0.5 in or smaller in
diameter and use solid insulating material. The outer conductor is usually copper or
aluminum braid and the insulating material is solid. The conductor is copper or
copper clad steel. The advantage with these cables is that they are inexpensive
and very to handle in terms of weight and flexibility.
For more information about these coax cables, look thru the attached
document Coax Cable Specifications:
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Coaxial Cables Continued…..
Connectors.
The connectors of these coaxial cables are either of a bayonet style coupling for
ease of assembly or a screw-type coupling for better protection from moisture.
The BNC connector, a bayonet style is used extensively with test equipment when
the cables need to be removed and reattached numerous number of times during
testing. For more information about these coax cables, look thru the attached
document Coax Cable connector Specifications:
Longer connections between the signal source and its antenna
For interconnection between a source and its antenna. The cable may be several
feet long and experience extreme environmental conditions. For high power
broadcast stations, the use of rigid coaxial transmission lines is very common.
Semi flexible use solid outer conductors that are fabricated form copper strips that
have been seam welded into continuous cylinders. For flexibility, the outers are
corrugated to permit bending to account for thermal expansion when exposed to
various temperatures. Solid foam dielectric materials or spiral wound dielectric
spacer is used to maintain the concentricity between the inner and outer
conductors. For even higher power higher power handling and lower attenuation
rigid coaxial transmission line can be used. These can range from 3 1/8 in diameter
to 8 3/16, mainly used in FM and TV transmission. Rigid coaxial transmission lines
table.
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Please view the attached documents for LDF5-50A, LDF7-50A, HJ5-50, HJ750A, HJ8-50B, HJ11-50, HJ9-50 cables and their connectors.
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Fiber:
An optical fiber or optical fiber is a thin, flexible, transparent fiber that acts as a
waveguide, or "light pipe", to transmit light between the two ends of the fiber. Optical
fibers are widely used in fiber-optic communications, which permits transmission over
longer distances and at higher bandwidths (data rates) than other forms of
communication. Fibers are used instead of metal wires because signals travel along
them with less loss and are also immune to electromagnetic interference. Fibers are
also used for illumination, and are wrapped in bundles so they can be used to carry
images, thus allowing viewing in tight spaces. Specially designed fibers are used for a
variety of other applications, including sensors and fiber lasers.
Optical fiber typically consists of a transparent core surrounded by a transparent
cladding material with a lower index of refraction. Light is kept in the core by total
internal reflection. This causes the fiber to act as a waveguide.
Types of Fibers:
Multi-Mode Fibers (MMF): Figure A, Slide 18, Also Figure B, Slide 18
These are fibers that can support many propagation paths or transverse modes.
Fiber with large core diameter (greater than 10 micrometers) is called multi-mode
fiber. In a step-index multi-mode fiber, rays of light are guided along the fiber core by
total internal reflection.
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Fiber:
Continued....
Rays that meet the core-cladding boundary at a high angle (measured relative to a
line normal to the boundary), greater than the critical angle for this boundary, are
completely reflected. The critical angle (minimum angle for total internal reflection) is
determined by the difference in index of refraction between the core and cladding
materials. Rays that meet the boundary at a low angle are refracted from the core into
the cladding, and do not convey light and hence information along the fiber. The
critical angle determines the acceptance angle of the fiber.
In graded-index fiber, the index of refraction in the core decreases continuously
between the axis and the cladding. This causes light rays to bend smoothly as they
approach the cladding, rather than reflecting abruptly from the core-cladding
boundary. The resulting curved paths reduce multi-path dispersion because high angle
rays pass more through the lower-index periphery of the core, rather than the highindex center. The index profile is chosen to minimize the difference in axial
propagation speeds of the various rays in the fiber. This ideal index profile is very
close to a parabolic relationship between the index and the distance from the axis.
Single-Mode Fibers (SMF): See figure B, Slide 18.
The waveguide analysis shows that the light energy in the fiber is not completely
confined in the core. Instead, especially in single-mode fibers, a significant fraction of
the energy in the bound mode travels in the cladding as an evanescent wave.
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Single Fiber Mode
Continued.....
The most common type of single-mode fiber has a core diameter of 8–10 micrometers
and is designed for use in the near infrared. The mode structure depends on the
wavelength of the light used, so that this fiber actually supports a small number of
additional modes at visible wavelengths. Multi-mode fiber, by comparison, is
manufactured with core diameters as small as 50 micrometers and as large as
hundreds of micrometers.
Materials:
Glass optical fibers are almost always made from silica, but some other materials,
such as fluorozirconate, fluoroaluminate, and chalcogenide glasses as well as
crystalline materials like sapphire, are used for longer-wavelength infrared or other
specialized applications. Silica and fluoride glasses usually have refractive indices of
about 1.5, but some materials such as the chalcogenides can have indices as high as
3. Typically the index difference between core and cladding is less than one percent.
Plastic optical fibers (POF) are commonly step-index multi-mode fibers with a core
diameter of 0.5 millimeters or larger. POF typically have higher attenuation coefficients
than glass fibers, 1 dB/m or higher.
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Practical Situations:
In practical fibers, the cladding is usually coated with a tough resin buffer layer, which
may be further surrounded by a jacket layer, usually glass. These layers add strength
to the fiber but do not contribute to its optical wave guide properties. Rigid fiber
assemblies sometimes put light-absorbing ("dark") glass between the fibers, to prevent
light that leaks out of one fiber from entering another. This reduces cross-talk between
the fibers, or reduces flare in fiber bundle imaging applications.
Modern cables come in a wide variety of sheathings and armor, designed for
applications such as direct burial in trenches, high voltage isolation, dual use as power
lines, installation in conduit, lashing to aerial telephone poles, submarine installation,
and insertion in paved streets.
Fiber cable can be very flexible, but traditional fiber's loss increases greatly if the fiber
is bent with a radius smaller than around 30 mm. This creates a problem when the
cable is bent around corners or wound around a spool. "Bendable fibers", targeted
towards easier installation in home environments, have been standardized as ITU-T
G.657. This type of fiber can be bent with a radius as low as 7.5 mm without adverse
impact.
Another important feature of cable is cable withstanding against the horizontally
applied force. It is technically called max tensile strength defining how much force can
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applied to the cable during the installation period.
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Practical Situations:
Continued....
Telecom Anatolia fiber optic cable versions are reinforced with aramid yarns or glass
yarns as intermediary strength member. In commercial terms, usage of the glass
yarns are more cost effective while no loss in mechanical durability of the cable. Glass
yarns also protect the cable core against rodents and termites
Figures:
Figure B: Fiber Types
Figure A: Multi-Mode Fiber
Figure C: Fiber
Cable Assembly
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Termination and splicing
Optical fibers are connected to terminal equipment by optical fiber connectors. These
connectors are usually of a standard type such as FC, SC, ST, LC, or MTRJ. Insert
document about the types of connectors
Optical fibers may be connected to each other by connectors or by splicing, that is,
joining two fibers together to form a continuous optical waveguide. The generally
accepted splicing method is arc fusion splicing, which melts the fiber ends together
with an electric arc. For quicker fastening jobs, a "mechanical splice" is used.
Fusion splicing is done with a specialized instrument that typically operates as follows:
The two cable ends are fastened inside a splice enclosure that will protect the splices,
and the fiber ends are stripped of their protective polymer coating (as well as the more
sturdy outer jacket, if present). The ends are cleaved (cut) with a precision cleaver to
make them perpendicular, and are placed into special holders in the splicer. The splice
is usually inspected via a magnified viewing screen to check the cleaves before and
after the splice. The splicer uses small motors to align the end faces together, and
emits a small spark between electrodes at the gap to burn off dust and moisture.
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Termination and Splicing
Continued……
Fibers are terminated in connectors so that the fiber end is held at the end face
precisely and securely. A fiber-optic connector is basically a rigid cylindrical barrel
surrounded by a sleeve that holds the barrel in its mating socket. The mating
mechanism can be "push and click", "turn and latch" ("bayonet"), or screw-in
(threaded).
A typical connector is installed by preparing the fiber end and inserting it into the rear
of the connector body. Quick-set adhesive is usually used so the fiber is held securely,
and a strain relief is secured to the rear. Once the adhesive has set, the fiber's end is
polished to a mirror finish. Various polish profiles are used, depending on the type of
fiber and the application. For single-mode fiber, the fiber ends are typically polished
with a slight curvature, such that when the connectors are mated the fibers touch only
at their cores. This is known as a "physical contact" (PC) polish. The curved surface
may be polished at an angle, to make an "angled physical contact" (APC) connection.
Such connections have higher loss than PC connections, but greatly reduced back
reflection, because light that reflects from the angled surface leaks out of the fiber
core; the resulting loss in signal strength is known as gap loss. APC fiber ends have
low back reflection even when disconnected.
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Waveguides:
In electromagnetics and communications engineering, the term waveguide may
refer to any linear structure that conveys electromagnetic waves between its
endpoints. However, the original and most common meaning is a hollow metal pipe
used to carry radio waves. This type of waveguide is used as a transmission line
mostly at microwave frequencies, for such purposes as connecting microwave
transmitters and receivers to their antennas, in equipment such as microwave
ovens, radar sets, satellite communications, and microwave radio links.
A dielectric waveguide employs a solid dielectric rod rather than a hollow pipe. An
optical fiber is a dielectric guide designed to work at optical frequencies.
Transmission lines such as microstrip, coplanar waveguide, stripline or coaxial may
also be considered to be waveguides.
The electromagnetic waves in (metal-pipe) waveguide may be imagined as
travelling down the guide in a zig-zag path, being repeatedly reflected between
opposite walls of the guide. For the particular case of rectangular waveguide, it is
possible to base an exact analysis on this view. Propagation in dielectric waveguide
may be viewed in the same way, with the waves confined to the dielectric by total
internal reflection at its surface. Some structures, such as Non-radiative dielectric
waveguide and the Goubau line, use both metal walls and dielectric surfaces to
confine the wave.
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Types of waveguides:
- Rectangular waveguide: This is the most commonly used form of waveguide
and has a rectangular cross section.
- Circular waveguide: Circular waveguide is less common than rectangular
waveguide. They have many similarities in their basic approach, although signals
often use a different mode of propagation.
- Circuit board stripline: This form of waveguide is used on printed circuit boards
as a transmission line for microwave signals. It typically consists of a line of a given
thickness above an earth plane. Its thickness defines the impedance.
Uses:
-Optical fibers applications
-In microwave, a waveguide guides microwaves from a magnetron were waves are
formed.
-In radar applications
-Stripline – Waveguides for printed circuit boards.
Note: For more information about waveguides and the related frequency
application, please view the document Waveguide Specs
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Sample Waveguides:
Rectangular Waveguide
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End
Thank you
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