PROJECT ON COAXIAL CABLE-ELECTROMAGNETICS

"COAXIAL CABLE"

Brief Contents:
Acknowledgement …………………………………………………………………… xi
Abstracts ……………………………………………………………………xii


1.Historical Background…………………………………...……………………1
2.Introduction………………………………………………………………… ...2
3.Construction………………………………………………………………..….4
4.Types of Co-axialCable…………………………………………………....….6
5.Properties…………………………..…………………............…………..….12
6.Signal Propagation…………………………………………………………...16
7.Co-axial Cable Selection…………………………….…………………..…..18
8.Co-axial Connector Information………………………………………….….21
9.Applications………………………..…………………………………..…….24
10.Advantages & Disadvantages……………………………………….....….28
11.Conclusion & Discussion………………………………………………… 30
Bibliography & References……………………………………………………31









Contents:
--------------------------------------------------Acknowledgement xi
Abstracts xii

Chapters:
1.HISTORICAL BACKGROUND 1
2.INTRODUCTION 2-3
3.CONSTRUCTION 4-5
4.TYPES OF COAXIAL
CABLE 6-11
4.1.On the Basis of Construction
4.1.1.Hard Line 6
4.1.2.Radiating or Leaky feeder 7
4.1.3.RG-6/U 7
4.1.4Triaxial Cable 8
4.1.5.Twin-axial Cable 8
4.1.6.Biaxial or Twin Lead 9
4.1.7.Semi Rigid 9
4.1.8.Rigid Line 10
4.2.On the Basis of Band 11
4.2.1.Broad Band Coaxial
Cable 11
4.2.2.Base Band Coaxial
Cable 11

5.PROPERTIES 12-15
5.1.Electrical Properties 12
5.1.2.Capacitance 12
5.1.2.Velocity of Propagation 13
5.1.3.Attenuation 14
5.1.4.Reflection Losses 14
5.1.5.Power Handling 14
5.2.Physical Properties 15
5.2.1.Physical Dimensions 15
5.2.2.Temperature Rating 15
5.2.3.Bend radius and Flex
Radius 15
5.2.4.Pulling Tension 15












6.SIGNAL PROPAGATION 16 -17
7.COAXIAL CABLE
SELECTION 18-20
7.1.Selecting Video cable 18
7.2.Cable Runs 19
7.3.Cable Termination 20

8.CO-AXIAL CONNECTOR
INFORMATION 21-23
8.1.Standard Types 21
8.2.Miniature Types 22
8.3.Micro-miniature Types 22
8.4.Sub-miniature Types 22
8.5.Precision Types 23
8.6.Flange Types 23
8.7.Quick-Lock Connectors 23

9.APPLICATIONS 24-27
9.1.Vedio Distribution 24
9.2.Microwave Transmission 25
9.3.Common Coaxial Cable
Impedance's & main uses 25-27

10.ADVANTAGES 28-29
10.1.Advantages 28
10.2.Disadvantages 29

11.CONCLUSION AND DISCUSSION
30
Bibliography & Reference 31
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57/58/59/60(BEX B 067 KEC)



Abstract

Actually report writing is the technical practice for the information of ten different categories of subjects.So,in this report we are trying to give some information on Co-axial Cable which includes the historical background –giving the some histories of coaxial cable patented, construction-material needed for coaxial cable and sort of coaxial cable that may exists in terms of construction and band of coaxial cable .It also widely focuses on the Properties like, Electrical and Physical. Signal propagation on coaxial cable is described in a better way.Moreover,this report includes the different coaxial connector information. It also helps to gain the knowledge on the selection of video cable and guidance in the daily use of electronic devices. Many of the Applications are being discussed.
This report is prepared by the collection of different materials with the help of renowned books and websites, which may give the present and current information about “Coaxial Cable.”




Acknowledgement

It is our pleasure to present this report on “Coaxial Cable” as it is one of the best ideas of report writing in the field of Engineering.
We Authors are thankful to our respected,Er.Naresh Kumar Chaudhari,a teacher on Electromagnetic of KEC who helped us and encourage to start and terminate this report. And We would like to acknowledge the project team members(BEX/B/067)whose enthusiasm, encouragement and support were indispensable.
We would like to give greet to the Library Section of KEC for providing the valuable books in finalizing this report and the Stationary of KEC for helping in printing and binding purpose.
Finally we are thankful to the Department of Electronics and Computer Engineering of Kantipur Engineering College for inspiring in such projectal activities.





Mahesh Thapa Magar
Mahesh Sapkota
Mohan Budhathoki
Kamal Byanjankar






1.Historical Background

• 1880 — Coaxial cable patented in England by Oliver Heaviside, patent no. 1,407
• 1884 — Siemens & Halske patent coaxial cable in Germany (Patent No. 28,978, 27 March 1884).
• 1894 — Oliver Lodge demonstrates waveguide transmission at the Royal Institution.
• 1929 — First modern coaxial cable patented by Lloyd Espenschied and Herman Affel of AT&T's Bell Telephone Laboratories. 1936 — First closed circuit transmission of TV pictures on coaxial cable, from the 1936 Summer Olympics in Berlin to Leipzig
• 1936 — World's first underwater coaxial cable installed between Apollo Bay, near Melbourne, Australia, and Stanley, Tasmania. The 300 km cable can carry one 8.5-kHz broadcast channel and seven telephone channels.
• 1936 — AT&T installs experimental coaxial telephone and television cable between New York and Philadelphia, with automatic booster stations every ten miles. Completed in December, it can transmit 240 telephone calls simultaneously.
• 1936 — Coaxial cable laid by the General Post Office (now BT) between London and Birmingham, providing 40 telephone channels.
• 1941 — First commercial use in USA by AT&T, between Minneapolis, Minnesota and Stevens Point, Wisconsin. L1 system with capacity of one TV channel or 480 telephone circuits.
• 1956 — First transatlantic coaxial cable laid, TAT-1.








2. Introduction

A coaxial cable is one that consists of two conductors that share a common axis. The inner conductor is typically a straight wire, either solid or stranded and the outer conductor is typically a shield that might be braided or a foil. Coaxial cable is a cable type used to carry radio signals, video signals, measurement signals and data signals. Coaxial cables exists because we can't run open-wire line near metallic objects (such as ducting) or bury it. We trade signal loss for convenience and flexibility. Coaxial cable consists of an insulated center conductor which is covered with a shield. The signal is carried between the cable shield and the center conductor. This arrangement give quite good shielding against noise from outside cable, keeps the signal well inside the cable and keeps cable characteristics stable.

fig .coaxial cable.
Coaxial cables and systems connected to them are not ideal. There is always some signal radiating from coaxial cable. Hence, the outer conductor also functions as a shield to reduce coupling of the signal into adjacent wiring. More shield coverage means less radiation of energy (but it does not necessarily mean less signal attenuation).
Coaxial cable are typically characterized with the impedance and cable loss. The length has nothing to do with a coaxial cable impedance. Characteristic impedance is determined by the size and spacing of the conductors and the type of dielectric used between them. For ordinary coaxial cable used at reasonable frequency, the characteristic impedance depends on the dimensions of the inner and outer conductors. The characteristic impedance of a cable (Zo) is determined by the formula 138 log b/a, where b represents the inside diameter of the outer conductor (read: shield or braid), and a represents the outside diameter of the inner conductor.
Most common coaxial cable impedance in use in various applications are 50 ohms and 75 ohms. 50 ohms cable is used in radio transmitter antenna connections, many measurement devices and in data communications (Ethernet). 75 ohms coaxial cable is used to carry video signals, TV antenna signals and digital audio signals. There are also other impedance in use in some special applications (for example 93 ohms). It is possible to build cables at other impedance, but those mentioned earlier are the standard ones that are easy to get. It is usually no point in trying to get something very little different for some marginal benefit, because standard cables are easy to get, cheap and generally very good. Different impedances have different characteristics. For maximum power handling, somewhere between 30 and 44 Ohms is the optimum. Impedance somewhere around 77 Ohms gives the lowest loss in a dielectric filled line. 93 Ohms cable gives low capacitance per foot. It is practically very hard to find any coaxial cables with impedance much higher than that. .













3. Construction

Coaxial cable design choices affect physical size, frequency performance, attenuation, power handling capabilities, flexibility, strength, and cost. The inner conductor might be solid or stranded; stranded is more flexible. To get better high-frequency performance, the inner conductor may be silver-plated. Sometimes copper-plated iron wire is used as an inner conductor.
The insulator surrounding the inner conductor may be solid plastic, a foam plastic, or air with spacers supporting the inner wire. The properties of dielectric control some electrical properties of the cable. A common choice is a solid polyethylene (PE) insulator, used in lower-loss cables. Solid Teflon (PTFE) is also used as an insulator. Some coaxial lines use air (or some other gas) and have spacers to keep the inner conductor from touching the shield.
Many conventional coaxial cables use braided copper wire forming the shield. This allows the cable to be flexible, but it also means there are gaps in the shield layer, and the inner dimension of the shield varies slightly because the braid cannot be flat. Sometimes the braid is silver-plated. For better shield performance, some cables have a double-layer shield.]The shield might be just two braids, but it is more common now to have a thin foil shield covered by a wire braid. Some cables may invest in more than two shield layers, such as "quad-shield," which uses four alternating layers of foil and braid. Other shield designs sacrifice flexibility for better performance; some shields are a solid metal tube. Those cables cannot take sharp bends, as the shield will kink, causing losses in the cable.
fig.Simple Construction


For high-power radio-frequency transmission up to about 1 GHz, coaxial cable with a solid copper outer conductor is available in sizes of 0.25 inch upward. The outer conductor is rippled like a bellows to permit flexibility and the inner conductor is held in position by a plastic spiral to approximate an air dielectric.
Coaxial cables require an internal structure of an insulating (dielectric) material to maintain the spacing between the center conductor and shield. The dielectric losses increase in this order: Ideal dielectric (no loss),vacuum, air, Polytetrafluoroethylene (PTFE), polyethylene foam, and solid polyethylene. A low relative permittivity allows for higher-frequency usage.

An inhomogeneous dielectric needs to be compensated by a non-circular conductor to avoid current hot-spots.Most cables have a solid dielectric; others have a foam dielectric that contains as much air as possible to reduce the losses. Foam coax will have about 15% less attenuation but can absorb moisture—especially at its many surfaces — in humid environments, increasing the loss. Supports shaped like stars or spokes are even better but more expensive. Still more expensive were the air-spaced coaxial used for some inter-city communications in the mid-20th Century. The center conductor was suspended by polyethylene discs every few centimeters. In some low-loss coaxial cables such as an RG-62 type, the inner conductor is supported by a spiral strand of polyethylene, so that an air space exists between most of the conductor and the inside of the jacket. The lower constant of air allows for a greater inner diameter at the same impedance and a greater outer diameter at the same cutoff frequency, lowering ohmic losses. Inner conductors are sometimes silver-plated to smooth the surface and reduce losses due to skin effect A rough surface prolongs the path for the current and concentrates the current at peaks and, thus, increases ohmic losses.
The insulating jacket can be made from many materials. A common choice is PVC, but some applications may require fire-resistant materials. Outdoor applications may require the jacket to resist ultraviolet and oxidation. For internal chassis connections the insulating jacket may be omitted.






4.Types of Coaxial Cable

4.1.On the Basis of Construction:
4.1.2.Hard line:


1-5/8" flexible line
Hard line is used in broadcasting as well as many other forms of radio communication. It is a coaxial cable constructed using round copper, silver or gold tubing or a combination of such metals as a shield. Some lower-quality hard line may use aluminum shielding, aluminum however is easily oxidized and unlike silver or gold oxide, aluminum oxide drastically loses effective conductivity. Therefore all connections must be air and water tight. The center conductor may consist of solid copper, or copper-plated aluminum. Since skin effect is an issue with RF, copper plating provides sufficient surface for an effective conductor. Most varieties of hard line used for external chassis or when exposed to the elements have a PVC jacket; however, some internal applications may omit the insulation jacket. Hard line can be very thick, typically at least a half inch or 13 mm and up to several times that, and has low loss even at high power. These large-scale hard lines are almost always used in the connection between a transmitter on the ground and the antenna or aerial on a tower. Hard line may also be known by trademarked names such as Helix (Andrew) or Cable wave (REFS/Cable wave).

Larger varieties of hard line may consist of a center conductor that is constructed from either rigid or corrugated copper tubing. The dielectric in hard line may consist of polyethylene foam, air, or a pressurized gas such as nitrogenous desiccated air (dried air). In gas-charged lines, hard plastics such as nylon are used as spacers to separate the inner and outer conductors.
The addition of these gases into the dielectric space reduces moisture contamination, provides a stable dielectric constant, and provides a reduced risk of internal arcing. Gas-filled hard lines are usually used on high-power RF transmitters such as television or radio broadcasting, military transmitters, and high-power amateur radio applications but may also be used on some critical lower-power applications such as those in the microwave bands.
4.1.2.Radiating or leaky feeder :
Leaky feeder is a communications system used in underground mining and other tunnel environments. It consists of a coaxial cable run along tunnels which emits and receives radio waves, functioning as an extended antenna. The cable is "leaky" in that it has gaps or slots in its outer conductor to allow the radio signal to leak into or out of the cable along its entire length. Because of this leakage of signal, line amplifiers are required to be inserted at regular intervals, typically every 350 to 500 metres, to boost the signal back up to acceptable levels. The signal is usually picked up by portable transceivers carried by personnel. Transmissions from the transceivers are picked up by the feeder and carried to other parts of the tunnel, allowing two-way radio communication throughout the tunnel system.The system has a limited range and because of the high frequency it uses, transmissions cannot pass through solid rock, which limits the system to a line-of-sight application. It does, however, allow two-way mobile communication.
This system is also used for underground mobile communication in mass transit railways. In Hong Kong the leaky feeder aerial was incorporated in the specification of the capital project and installed during construction. This allows emergency services seamless mobile communication from the underground to the surface.
5.1.3.RG-6/U:

Fig.RG-6/U
RG-6/U is a common type of coaxial cable used in a wide variety of residential and commercial applications. The term "RG-6" itself is quite generic and refers to a wide variety of cable designs, which differ from one another in shielding characteristics, center conductor composition, and dielectric type. "RG" was originally a unit indicator ("Radio Guide") for bulk radio frequency (RF) cable in the U.S. military's Joint Electronics Type Designation System. The suffix "/U" means “for general utility use.”
The number was assigned sequentially. The "RG" unit indicator is no longer part of the JETDS system (MIL-STD-196E) and cable sold today under the RG-6 label does not necessarily meet military specifications. In practice, the term "RG-6" is generally used to refer to coaxial cables with an 18 AWG center conductor and 75 ohmcharacteristic impedance. RG-6 is insulated with an aluminum foil sheath. Even though RG-59 looks similar to RG-6, RG-59 is insulated with a copper foil sheath.

4.1.4.Triaxial Cable:

Fig.Triaxial Cable
Triaxial Cable, often referred to as triax for short, is a type of electrical cable similar to coaxial cable, but with the addition of an extra layer of insulation and a second conducting sheath. It provides greater bandwidth and rejection of interference than coax, but is more expensive. It is most commonly used in the television industry as a connecting cable between a camera and its CCU. The outer sheath is commonly used as a protective earth conductor. The core provides both power and signal connections, with the return for the power being provided through the inner screen. Through frequency-division multiplexing, the camera can send audio and video signals along the triax while the CCU can send camera control information, such as exposure settings, intercom, return audio and video (usually that of the program), and tally (a signal alerting the operator that their camera is on the air)and power for the camera.
Venues that host television productions fairly often, such as sports arenas, will usually have triaxial cables run from the location of the TV truck to common camera locations throughout the building. This allows a shorter and easier workday for visiting television crews, who can simply plug into existing cable runs instead of having to run their own and tear them down after the shoot.
5.1.5.Twin-axial cable :Twin-axial cable or twinax is a balanced, twisted pair within a cylindrical shield. It allows a nearly perfect differential signal which is both shielded and balanced to pass through. Multi-conductor coaxial cable is also sometimes used.



4.1.6.Biaxial or Twin-lead:
fig. Biaxial or Twin-lead.
Twin-lead is constructed of two multistranded copper or copper clad steel wires, held a precise distance apart by a plastic (usually polyethylene) ribbon. The uniform spacing of the wires is the key to the cable's function as a parallel transmission line; any abrupt changes in spacing would reflect radio frequency power back toward the source. The plastic also covers and insulates the wires. In 300 ohm twin-lead, the wire is usually 20 or 22 gauge, about 7. 5 mm (0.30 inches) apart.
Twin lead and other types of parallel transmission line are mainly used to connect radio transmitters and receivers to their antennas. Parallel transmission line has the advantage that its losses are an order of magnitude smaller than coaxial cable, the main alternative form of transmission line. Its disadvantages are that it is more vulnerable to interference, and must be kept away from metal objects which can cause power losses. For this reason, when installed along the outside of buildings and on antenna masts, standoff insulators must be used.
Twin-lead is supplied in several different sizes, with values of 600, 450, 300, and 75 ohms characteristic impedance. The most common, 300 ohm twin-lead, was once widely used to connect television sets and FM radios to their receiving antennas. 300 ohm twin-lead for television installations has been largely replaced with 75 ohm coaxial cable feed lines. Twin-lead is also used in radio stations as a transmission line for balanced transmission of radio frequency signals.
4.1.7.Semi-rigid:
Semi-rigid cable is a coaxial form using a solid copper outer sheath. This type of coax offers superior screening compared to cables with a braided outer conductor, especially at higher frequencies. The major disadvantage is that the cable, as its name implies, is not very flexible, and is not intended to be flexed after initial forming. (See "hard line")
Conformable cable is a flexible reform able alternative to semi-rigid coaxial cable used where flexibility is required. Conformable cable can be stripped and formed by hand without the need for specialist tools, similar to standard coaxial cable.

4.1.8.Rigid line:

Fig. Rigid Line
Rigid line is a coaxial formed by two copper tubes supported every other meter using PTFE-supports. Rigid lines are not possible to bend, so they often need elbows. Interconnection with rigid line is done with an inner bullet/inner support and a flange or connection kit. Rigid line is mainly used indoors for interconnection between transmitter and other RF-components, but even more rigid rigid line with flanges is used outdoors in antenna masts etc. With a flange connector it is possible to go from rigid line to hard line. Many broadcasting antennas and antenna splitters uses the flanged rigid line interface even when connecting to flexible coaxial cables and hard line.Rigid line is produced in a number of different sizes:
Outer conductor Inner conductor
Size Outer diameter (not flanged) Inner diameter Outer diameter Inner diameter
7/8" 22.2 mm 20 mm 8.7 mm 7.4 mm
1 5/8" 41.3 mm 38.8 mm 16.9 mm 15.0 mm
3 1/8" 79.4 mm 76.9 mm 33.4 mm 42.6 mm
4 1/2" 106 mm 103 mm 44.8 mm 42.8 mm
6 1/8" 155.6 mm 151.9 mm 66.0 mm 64.0 mm



4.2.On the Basis Of Bands:
4.2.1.BroadBandCoaxialCable:
Broadband LANs are multichannel typically based on coaxial cable as the transmission media, although fiber optic cable is also used. Individual channels offer bandwidth of 1 to 5 Mbps, with 20 to 30 channels typically Aggregate bandwidth is as much 500MHz. The characteristics may be given as Follows :
-Digital Signal onto RF carrier (Analog)
-Channel allocation based on FDM.
-Head-End for bi-directional transmission.
-Stations connected via RF modems radio modems accomplish the digital-to- analog ---Conversion process. providing the transmitting device access to an analog channel.
Advantages of Broadband :
-Data, voice and video can be accomplished on broadband channel.
-Greater distances.
-Greater bandwidth.
Disadvantages of Broadband :
-Cable Design
-Alignment and maintenance
-High cost, requires modems
-Lack of well developed standards.
5.2.2.Base band coaxial Cable:
Baseband LAN is single channel, supporting a single communication at a time. They are digital in nature. The total bandwidth of 1 to 100 Mbps is provided over coaxial cable, UTP,STP or fiber optic cable. Distance limitations depend on the medium employed and the specifics of the LAN protocol. Baseband LAN are the most popular and the most highly standarilized. Ethernet, Token passing, Token Ring and FDDI LANs are all baseband. They are intended only for data, as data communication is, after all, the primary reason for the existence of LANs. The characteristics of this system may be summarized as follows :
-Unmodulated digital signal.
-Single channel.
-Bi-directional propagation via T connectors.
-No need of modems-low cost installation
Advantages of Baseband :
-Simplicity and Low cost
-Ease of installation and maintenance and High rates
Disadvantages of Baseband :
-Limited distance and transmission of Data and voice only .
5. Properties

5.1.Electrical Properties:
The most common electrical property referred to in coax cable is the characteristic impedance, or simply 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, capacitance, inductance, and conductance, and is the equivalent value of these items combined. It is the most important characteristic to discuss since it is derived from all the other electrical properties in the cable. It is not length dependent, and is expressed in Ohms. Coax cable is typically designed as 50 ohm, 75 ohm, and 93 ohm depending upon the application. The characteristic impedance of a coaxial cable is determined by the relation of outer conductor diameter to inner conductor diameter and by the dielectric constant of the insulation.
The impendence of the coaxial cable changes somewhat with the frequency. Impedance changes with frequency until resistance is a minor effect and until dielectric dielectric constant is table. Where it levels out is the "characteristic impedance". The frequency where the impedance matches to the characteristic impedance varies somewhat between different cables, but this generally happens at frequency range of around 100 kHz (can vary). A simple formula to determine the impedance of a coaxial cable is:
Zo=138*Vp*log10(D/d)
Where: Zo = Characteristic Impedance
Vp = Velocity of Propagation
D = Diameter of the Dielectric
d = Diameter of the Conductor
Characteristic Impedance is commonly measured using a Time Domain Reflect meter (TDR), such as a Tektronix 11801C digital sampling oscilloscope with SD-24 TDR/sampling head, on a 10 ft. length of cable (2).


5.1.1.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. Capacitance is length dependent and is expressed in pF/ft

C = 7.36*εr
log10(D/d)

Where: εr = Dielectric Constant

Capacitance is commonly measured using a capacitance meter, such as a Hewlett-Packard 4194A Impedance/Gain-Phase Analyzer, at 1 kHz on a 10 ft. length of cable.

5.1.2.Velocity of Propagation:

Velocity of Propagation is the speed at which a signal travels through the cable with respect to the speed of light. This value is typically represented as a percentage of the
speed of light in free space. For example, solid PE is 66% while foam PE may be as high as 87%. This may be an important attribute if running several signals/cables in parallel, as it is important for all signals to arrive at (generally) the same time. This attribute may also be referred to as delay (nS/ft).
Vp=1/(εr)1/2
Delay =1.01674*(εr)1/2
Velocity is commonly measured using the resonance method on a network analyzer, such as the Hewlett-Packard 8751A, on a 10 – 15 ft. length of cable. Essential properties of coaxial cables are their characteristic impedance and its regularity, their attenuation as well as their behavior concerning the electrical separation of cable and environment, i.e. their screening efficiency. In applications where the cable is used to supply voltage for active components in the cabling system, the DC resistance has significance. Also the cable velocity information is needed on some applications. The coaxial cable velocity of propagation is defined by the velocity of the dielectric. It is expressed in percents of speed of light. Here is some data of come common coaxial cable insulation materials and their velocities:
Polyethylene (PE) 66%
Teflon 70%
Foam 78..86%



5.1.3.Attenuation:

Attenuation is the inherent signal power loss within the cable. It is dependent upon the cable design and is both frequency and length dependent. It is most effected by DC resistance of the center conductor and dissipation factor of the dielectric material. Attenuation is typically expressed in db/100ft.
Attenuation is commonly measured using a network analyzer, such as the Agilent 8753ES on a 100 ft. length of cable.
5.1.4.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 typically as a result of minute physical changes 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 (frequency). This loss can be minimized by quality cable manufacturing techniques and proper installation practices. This reflective losses typically expressed as Structural Return Loss (SRL) or Return Loss (RL) in dB for 75 ohm cables and as Voltage Standing Wave Ratio (VSWR) for 50 ohm cables. The difference between these values is that SRL is a measurement of impedance variation within the cable with respect to the actual cable characteristic impedance, while RL and VSWR measure variation from a fixed source impedance. This can be an important difference if the application can not compensate for cable impedance mismatch. Return Loss is commonly measured using a network analyzer, such as the Agilent 8753ES (with option 010), on a 150 ft. length of cable.
5.1.5.Power Handling:
Power Handling capability is dependent on the thermal dissipation and maximum voltage withstand properties of the cable design. The power rating is based upon the permissible rise in temperature above ambient, and is mostly dependent upon the temperature
properties of the dielectric material. The values typically assume a low RL or VSWR value and 20C ambient temperature in air. Burying cables, or other installation variances, will alter this capability. Manufacturers typically publish this data for transmission lines, and may have it available by special request for other cables.


5.2.Physical Properties: The mechanical and physical properties may be critical in selecting the appropriate cable for the application.


5.2.1.Physical Dimensions:

Physical Dimensions are critical to assure that an industry standard connector is available. Other odd-size dimensions will require use of a custom termination. Diameter of the center conductor, core, and jacket are the critical values.
5.2.2.Temperature Rating:

Temperature Rating which may be listed as operational or storage, provides the limitations on temperature extremes that the cable material can handle. This safe range, based upon the thermal properties of the dielectric and jacket materials, assures that the product will not fracture, melt, or otherwise deform resulting in electrical or mechanical failures.

5.2.3.Bend Radius and Flex Radius:
Bend Radius and Flex Radius are the minimum values for these attributes. Adherence to these guidelines will minimize the degradation of the cable due to cold flow and other stress/material properties in the application. Bend radius is for permanent install and flex radius is for flexing. Flex radius should not be misunderstood to mean that the cable is designed for continuous flexing.
5.2.4.Pulling Tension:
Pulling Tension is the maximum load bearing weight for the cable. 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 resulting in electrical performance problems in the cable.






6. Signal Propagation

Open-wire transmission lines have the property that the electromagnetic wave propagating down the line extends into the space surrounding the parallel wires. These lines have low loss, but also have undesirable characteristics. They cannot be bent, twisted, or otherwise shaped without changing their characteristic impedance, causing reflection of the signal back toward the source. They also cannot be run along or attached to anything conductive, as the extended fields will induce currents in the nearby conductors causing unwanted radiation and detuning of the line. Coaxial lines solve this problem by confining virtually all of the electromagnetic wave to the area inside the cable. Coaxial lines can therefore be bent and moderately twisted without negative effects, and they can be strapped to conductive supports without inducing unwanted currents in them.

Fig, General Signal propagation in coaxial cable



In radio-frequency applications up to a few gigahertz, the wave propagates primarily in the transverse electric magnetic (TEM) mode, which means that the electric and magnetic fields are both perpendicular to the direction of propagation. However, above a certain cutoff frequency, transverse electric (TE) and/or transverse magnetic (TM) modes can also propagate, as they do in a waveguide. It is usually undesirable to transmit signals above the cutoff frequency, since it may cause multiple modes with different phase velocities to propagate, interfering with each other. The outer diameter is roughly inversely proportional to the cutoff frequency. A propagating surface-wave mode that does not involve or require the outer shield but only a single central conductor also exists in coax but this mode is effectively suppressed in coax of conventional geometry and common impedance. Electric field lines for this [TM] mode have a longitudinal component and require line lengths of a half-wavelength or longer.
Coaxial cable may be viewed as a type of waveguide. Power is transmitted through the radial electric field and the circumferential magnetic field in the TEM00 transverse mode. This is the dominant mode from zero frequency (DC) to an upper limit determined by the electrical dimensions of the cable.














7.Coaxial Cable Selection

7.1.Selecting Video Cable:

There are two factors that govern the selection of cable: the location of cable runs, either indoor or outdoor, and the maximum length of the individual cable runs.
Video coaxial cable is designed to transmit maximum signaling energy from a 75 ohm source to a 75 ohm load with minimum signal loss. Excessive signal loss and reflection occurs if cable rated for other than 75 ohms is used. Cable characteristics are determined by a number of factors (core material, dielectric material and shield construction, among others) and must be carefully matched to the specific application. Moreover, the transmission characteristics of the cable will be influenced by the physical environment through which the cable is run and the method of installation.Use only high quality cable and be careful to match the cable to the environment (indoor or outdoor). Solid core, bare-copper conductor is best suited to video applications, except where flexing occurs. In locations where the cable must be continuously flexed (i.e., when used with scanners or pan & tilts), use cable intended for such movement. This cable will have a stranded wire core. Use only cable with pure copper stranding. Do not use cable with copper-plated steel stranding because it does not transmit effectively in the frequency range used in CCTV.
The preferred dielectric material is foam polyethylene. Foam polyethylene has better electrical characteristics and offers the best performance over solid polyethylene, but it is more vulnerable to moisture. Use cable with solid polyethylene dielectric in applications subject to moisture.
In the average CCTV installation, with cable lengths of less than 750 feet (228 m),RG59/U cable is a good choice. Having an outside dimension of approximately 0.25 inches, it comes in 500-and 1,000-foot rolls.For short cable runs, use RG59/U with a 22-gauge center conductor, which has a DC resistance of about 16 ohms per 1,000 feet (304 m). For longer runs, the 20-gauge variety which has a DC resistance of approximately 10 ohms per 1,000 feet will work well. In either case, cables with polyurethane or polyethylene as the dielectric material are readily available.
For installations requiring cable runs between 800 (244 m) and 1,500 feet (457 m),RG6/U is best. Having the same electrical characteristics as RG59/U, its outer dimension also is about equal to that of RG59/U.RG6/U comes in 500-,1000-and 2000-foot rolls, and it may be obtained in a variety of dielectric and outer-jacket materials. Due to its large-diameter center conductor of about 18 gauge,RG6/ U has a DC resistance of approximately 8 ohms per 1,000 feet (304 m) and can deliver a signal farther than RG59/U.

Use RG11/U to exceed the capability of RG6/U. Once again, the electrical characteristics of this cable are basically the same as the others. The center conductor can be ordered in 14-or 18-gauge sizes, producing a DC resistance of approximately 3-8 ohms per 1,000 feet (340 m). Being the largest of the three cables at 0.405 inches, it is more difficult to handle and install.RG11/U cable usually is delivered in 500-,1000-and 2000-foot rolls.
Because of special applications, variations of RG59/U, RG6/U and RG11/U frequently are introduced by manufacturers.Due to changes in fire and safety regulations throughout the country, Teflon and other fire-retardant materials are becoming more popular as outer-jacket and dielectric materials. In case of a fire, these materials do not give off the same poisonous fumes as PVC-type cables, and therefore, are considered safer.

For underground applications, direct burial cables, made specifically for that purpose are recommended. The outer jacket of this type of cable contains moisture-resisting and other materials that protect the cable, allowing it to be placed directly into a trench.With numerous choices available, finding the right video cable for each camera application should be easy. After the installation has been properly assessed, read the equipment specifications and complete the appropriate calculations.
7.2.Cable Runs:
Although coax cable has built-in losses, the longer and smaller the cable is, the more severe the losses become; and the higher the signal frequency, the more pronounced the losses. Unfortunately this is one of the most common and unnecessary problems currently plaguing CCTVsecurity systems as a whole.
If, for example, your monitor is located 1,000 feet (304 m) from the camera, approximately 37-percent of the high frequency information will be lost in transmission. The unfortunate aspect of this condition is that it is not obvious. You cannot see information that is not there and may not even realize that information has been deleted. Because many CCTV security systems have cable runs that exceed several thousand feet, unless you are aware of this characteristic of cable, your system may be providing a seriously degraded image.

So, if your cameras and monitors are separated by lengths greater than 750 feet (228 m), you should check to make certain that some provision has been made to guarantee the video signal's transmission strength.
Cable Type* Maximum Distance
RG59/U 750 ft.
RG6/U 1,000 ft.
RG11/U 1,500 ft.

*Minimum cable requirements:
75 ohms impedance
All-copper center conductor
All-copper braided shield with 95% braid coverage


7.3.Cable Termination:
In video security systems, camera signals must travel from the camera to the monitor. The method of transmission is usually "coax" cable. Proper termination of cables is essential to a system's reliable performance.Because the characteristic impedance of coax cable ranges from 72 to 75 ohms, it is necessary that the signal travels on a uniform path along any point in the system to prevent any picture distortion and to help ensure proper transfer of the signal from the camera to the monitor. The impedance of the cable must remain constant with a value of 75 ohms. To properly transfer power between two video devices with acceptable losses, the signal output from the camera must match the input impedance of the cable, which in turn must match the input impedance of the monitor. The end point of any video cable run must be terminated in 75 ohms. Usually, the cable run will end at the monitor, which will ensure that this requirement is met. Usually the video input impedance of the monitor is controlled by a switch located near the looping video (input/output) connectors. This switch allows for either 75 ohm termination if the monitor is the "end point”, or Hi-Z for looping to a second monitor. Check equipment specifications and instructions to determine the proper termination requirements. Failure to terminate signals properly usually results in a high contrast, slightly grainy picture. Ghosting and other signal imperfections also may be evident.







8. Coaxial Connector Information

A coaxial RF connector is an electrical connector designed to work at radio frequencies in the multi-megahertz range. RF connectors are typically used with coaxial and are designed to maintain the shielding that the coaxial design offers. Better models also minimize the change in transmission line impedance at the connection. Mechanically, they provide a fastening mechanism (thread, bayonet, braces, push pull) and springs for a low holmic electric contact while sparing the gold surface, thus allowing above 1000 reconnects and reducing the insertion force. Research activity in the area of radio-frequency (RF) circuit design has surged in the last decade in direct response to the enormous market demand for inexpensive, high-data-rate wireless transceivers.
Types:


Fig. The coaxial connector Miniquick
8.1.Standard types
• 7/16 DIN connector, a high-power 50 Ω connector originally developed by Spinner
• BNC connector (Bayonet Neill-Concelman)
• Blind mate BMA, also known as OSP (Omni Spectra push-on)
• C connector (Concelman)
• F connector, used for domestic television installations and domestic satellite LNBs (75 Ω) world wide.
• GR connector (General Radio)
• HN connector, a high voltage version of the N connector
IEC 169-2 connector, also called Belling Lee connector or PAL, used throughout Europe and some other countries for domestic television installations and asFM connector for radio. It is standardized in EN 60169-2.
Motorola connector, standard AM/FM antenna connector used for automotive radios
Musa connector, a 50 Ω connector used in telecommunications and broadcast video
• N connector (Neill)
• NMO mount (new Motorola mount), for removable mobile antennas. Large threaded base for durability in wind.
• SC connector, screw version of C connector
• SMA connector, SubMiniature version A - also listed below in Subminiatures - is a very popular lab equipment standard connector.
• TNC connector (threaded Neill-Concealment)
• UHF connector (e.g., PL-259/SO-239). Also referred to as an M-type connector by Japanese manufacturers such as Kenwood
8.2.Miniature types
• Miniature BNC connectors
• Miniature UHF connectors
• DIN 47223 connectors
• IPX connector
• SMZ connector - System 43 (BT43 and High Density HD43) for use in DDF
8.3.Micro-miniature types
• IMP connector
• MMT connector
• MMS connector
• U.FL connector
• UMP connector
8.4.Sub-miniature types
• MCX connector
• MMCX connector
• FME connector
• SMA connector, including variants:
• 3.5 and 2.92 mm connectors, which cross-mate with SMA, and
• 2.4, 1.85 and 1.0 mm connectors, which do not cross-mate with SMA
• SMB connector
• SMC connector
• SMP connector

8.5.Precision types
APC-7 connector
8.6.Flange connectors
EIA RF Connectors series of RF flange connectors
8.7.Quick-lock connectors
• QMA and QN connector
• QLS connector
• Snap connector
• Mini-QMA connector
• WQMA (Waterproof QMA)




Fig. Different types of connectors.



9. Applications


9.1.Video distribution:
One of the broadest uses of coaxial cable is for video distribution. From CATV signals around the neighborhood to precision digital signals in a post-production studio, these signals are routed on 75 ohm coaxial cable. Broadband CATV (or MATV) signals typically use a series 59 (RG-59) or series 6 (RG-6) type coaxial cable, or drop cable. These cables use copper covered steel conductors and aluminum foil/braid combination shields (outer conductors). They are designed for use above 50 MHz, with high strength, low weight and low cost the primary factors. These cables are all typically designed to a SCTE standard and are a commodity-type item. Electrical performance is good and clearly defined in the industry standards. Cables used in outdoor environments typically utilize a polyethylene jacket material. The distribution trunk cable is series 11 (RG-11) type or larger – typically “hard line” cable utilizing a corrugated copper outer conductor. These cables are designed for minimum attenuation and good power handling capability.

Another type of 75 ohm video cable is standard video cable. These cables are based upon standard RG-type designs, utilizing copper covered steel, copper, or tinned copper conductors and bare or tinned copper braid only shields. This cable is used primarily for CCTV, security, surveillance, and other “non-critical” video applications – video for consumption that will not be manipulated, saved, or used for other purposes. These cables are not typically associated with an industry standard, so there is much variation and differentiation among available designs. Typical cables specify nominal electrical values only.

The high end of video cables is precision video cable. These cables are loosely based upon the standard RG-type designs. They have solid bare copper conductors, foam dielectric, combination foil and 95% tinned copper braid shields. They are designed for maximum bandwidth, minimum return loss, and minimum attenuation loss. The cables have very tight requirements on all electrical attributes and are used for both analog and digital video in broadcast, post-production, and other critical video applications.
There are also many specialty types of video cables, such as S-VHS, RGB, DBS, and Triad to name a few


9.2.Microwave transmission:
Cables used for two-way communication, RF and microwave transmission, data transmission and instrumentation/control are typically 50 ohm coaxial cables. These cables are based upon MIL-Spec designs and are most often referred to by their RG type number. The cables fall into a few categories: Transmission and computer cables that are based upon RG type designs, but not per the current MIL-Spec; MIL-C-17 QPL cables that are in compliance with the current MIL-Spec; and low-loss cables based loosely upon RG type designs. The RG type cables are the most used products since the majority of cable applications do not require QPL cables.
Furthermore, most manufacturers have a limited availability of QPL cables for this reason. The major differences between the cables are typically the type of PVC jacket material used and less stringent electrical and physical requirements. For wireless and antenna applications, the low-loss cables are gaining popularity because of their size, weight, cost, and performance advantages over the traditional designs. These cables typically utilize a foamed dielectric material and combination foil/braid shields.

Other impedance cables are used for data transmission and instrumentation/control. These are typically 93 ohm or 125 ohm and are not as common as they once were. As with the transmission and computer cables, the majority of cables used are RG type cables with minimal use of QPL product.

Specialty coaxial cables include low-noise and musical interconnects cables. These are specially designed to minimize piezoelectric and turboelectric noise in cables and are not for RF use. The cables may be loosely based upon RG type designs, but utilize semi-conductive material layers within the cable.
9.3.Common coaxial cable impedances and their main uses:
Most common coaxial cable impedances in use in various applications are 50 ohms and 75 ohms. 50 ohms cable is used in radio transmitter antenna connections, many measurement devices and in data communications (Ethernet). 75 ohms coaxial cable is used to carry video signals, TV antenna signals and digital audio signals. There are also other impedances in use in some special applications (for example 93 ohms).
It is possible to build cables at other impedances, but those mentioned earlier are the standard ones that are easy to get. It is usually no point in trying to get something very little different for some marginal benefit, because standard cables are easy to get, cheap and generally very good. Different impedances have different characteristics. For maximum power handling, somewhere between 30 and 44 Ohms is the optimum. Impedance somewhere around 77 Ohms gives the lowest loss in a dielectric filled line. 93 Ohms cable gives low capacitance per foot. It is practically very hard to find any coaxial cables with impedance much higher than that. Here is a quick overview of common coaxial cable impedances and their main uses:
• 50 ohms: 50 ohms coaxial cable is very widely used with radio transmitter applications. It is used here because it matches nicely to many common transmitter antenna types, can quite easily handle high transmitter power and is traditionally used in this type of applications (transmitters are generally matched to 50 ohms impedance). In addition to this 50 ohm coaxial cable can be found on coaxial Ethernet networks, electronics laboratory interconnection (foe example high frequency oscilloscope probe cables) and
• high frequency digital applications (fe example ECL and PECL logic matches nicely to 50 ohms cable). Commonly used 50 Ohm constructions include RG-8 and RG-58.
• 60 Ohms: Europe chose 60 ohms for radio applications around 1950s. It was used in both transmitting applications and antenna networks. The use of this cable has been pretty much phased out, and nowdays RF system in Europe use either 50 ohms or 75 ohms cable depending on the application.
• 75 ohms: The characteristic impedance 75 ohms is an international standard, based on optimizing the design of long distance coaxial cables. 75 ohms video cable is the coaxial cable type widely used in video, audio and telecommunications applications. Generally all baseband video applications that use coaxial cable (both analogue and digital) are matched for 75 ohm impedance cable. Also RF video signal systems like antenna signal distribution networks in houses and cable TV systems are built from 75 ohms coaxial cable (those applications use very low loss cable types). In audio world digital audio (S/PDIF and coaxial AES/EBU) uses 75 ohms coaxial cable, as well as radio receiver connections at home and in car. In addition to this some telecom applications (for example some E1 links) use 75 ohms coaxial cable. 75 Ohms is the telecommunications standard, because in a dielectric filled line, somewhere around 77 Ohms gives the lowest loss. For 75 Ohm use common cables are RG-6, RG-11 and RG-59.
93 Ohms: This is not much used nowadays. 93 ohms was once used for short runs such as the connection between computers and their monitors because of low capacitance per foot which would reduce the loading on circuits and allow longer cable runs. In addition thsi was used in some digital commication systems (IBM 3270 terminal networks) and some early LAN systems fig. Use of Coaxial Cable in Cameras.

use in cc camera




Use in photo camera
10.Advantages and Disadvantages


10.1.Advantages:

Broadband system
Coax has a sufficient frequency range to support multiple channels, which allows for much greater throughput.
Greater channel capacity
Each of the multiple channels offers substantial capacity. The capacity depends on where you are in the world. In the North American system, each channel in the cable TV system is 6MHz wide, according to the National Television Systems Committee (NTSC) standard. In Europe, with the Phase Alternate Line (PAL) standard, the channels are 8MHz wide. Within one of these channels, you can provision high-speed Internet access-that's how cable modems operate. But that one channel is now being shared by everyone using that coax from that neighborhood node, which can range from 200 to 2,000 homes.
Greater bandwidth
Compared to twisted-pair, coax provides greater bandwidth systemwide, and it also offers greater bandwidth for each channel. Because it has greater bandwidth per channel, it supports a mixed range of services. Voice, data, and even video and multimedia can benefit from the enhanced capacity.
Lower error rates
Because the inner conductor is in a Faraday shield, noise immunity is improved, and coax has lower error rates and therefore slightly better performance than twisted-pair. The error rate is generally 10-9 (i.e., 1 in 1 billion) bps.
Greater spacing between amplifiers
Coax's cable shielding reduces noise and crosstalk, which means amplifiers can be spaced farther apart than with twisted-pair.





10.2.Disadvantages
Problems with the deployment architecture
The bus topology in which coax is deployed is susceptible to congestion, noise, and security risks.
Bidirectional upgrade required
In countries that have a history of cable TV, the cable systems were designed for broadcasting, not for interactive communications. Before they can offer to the subscriber any form of two-way services, those networks have to be upgraded to bidirectional systems.
Great noise
The return path has some noise problems, and the end equipment requires added intelligence to take care of error control.
High installation costs
Installation costs in the local environment are high.
Susceptible to damage from lightning strikes
Coax may be damaged by lightning strikes. People who live in an area with a lot of lightning strikes must be wary because if that lightning is conducted by a coax, it could very well fry the equipment at the end of it.














11.Conclusion and Discussion

During the preparation of this report on “Coaxial cable”, we have faced some of the problems due to which we are not able to prepare this report as we wished and planned. But Beyond the problems and obstacles we have prepared this report as much as better that can give more information on Coaxial Cables.Some of the points related about report which helps the readers & others to become clear of our vision, & also about our problems during the preparation.
Finally, this report on Coaxial Cable carried out has really make us to reveal the basic preliminaries about the Coaxial Cable. It helps us to gain the knowledge about Coaxial cable in the daily life. It also helps us to know about the different applications in the different fields. This report has given information on Coaxial Connectors for the required Cable. How the signals propagates through the Cable, data and information passes in the equipments can known from this report.
Moreover, this report may not include the some more information about Coaxial Cable. Though it has minor discussion it gives full and complete information in this level.













Bibliography and References

 Hayt,W.H.Engineering Electromagnetics,New Delhi,Tata McGraw Hill,2006.

 MartinJ_VanDer Burgt.”Coaxial Cables and Applications”


 H.P.Westmanetal---(ed),References Data for Radio Engineers, fifth Eddition,1968.Howard w.Sams and co.

 www.http://en.wikipedia.org/wiki/coaxial_cable.


 www.webopedia.com/TERM/Coaxial_cable:html.

 www.fairviewmicrowave.com


 www.accesscomm.com/au/reference/coax.html

 www.radio_electronics.com/info/coax/rf_coaxial-feeder-cable.php


 www.belden.com/pdfs/Techpprs/coaxialcables and Applications.pdf