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6.2 Wireline channels

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The analysis and transfer characteristics of wireline channels.

Wireline channels were the first used for electrical communications in the mid-nineteenth century for the telegraph.Here, the channel is one of several wires connecting transmitter to receiver. The transmitter simply creates a voltage relatedto the message signal and applies it to the wire(s). We must have a circuit—a closed path—that supports current flow. In thecase of single-wire communications, the earth is used as the current's return path. In fact, the term ground for the reference node in circuits originated in single-wire telegraphs. You can imagine that the earth's electricalcharacteristics are highly variable, and they are. Single-wire metallic channels cannot support high-quality signaltransmission having a bandwidth beyond a few hundred Hertz over any appreciable distance.

Coaxial cable cross-section

Coaxial cable consists of one conductor wrapped around the central conductor. This type of cable supports broaderbandwidth signals than twisted pair, and finds use in cable television and Ethernet.

Consequently, most wireline channels today essentially consist of pairs of conducting wires ( [link] ), and the transmitter applies a message-related voltage across the pair. How these pairs of wires arephysically configured greatly affects their transmission characteristics. One example is twisted pair , wherein the wires are wrapped about each other. Telephonecables are one example of a twisted pair channel. Another is coaxial cable , where a concentric conductor surrounds a central wire with a dielectric material in between.Coaxial cable, fondly called "co-ax" by engineers, is what Ethernet uses as its channel. In either case, wireline channelsform a dedicated circuit between transmitter and receiver. As we shall find subsequently, several transmissions can share thecircuit by amplitude modulation techniques; commercial cable TV is an example. These information-carrying circuits are designedso that interference from nearby electromagnetic sources is minimized. Thus, by the time signals arrive at the receiver,they are relatively interference- and noise-free.

Both twisted pair and co-ax are examples of transmission lines , which all have the circuit model shown in [link] for an infinitesimally small length. This circuit model arisesfrom solving Maxwell's equations for the particular transmission line geometry.

Circuit model for a transmission line

The so-called distributed parameter model for two-wire cables has the depicted circuit model structure. Element valuesdepend on geometry and the properties of materials used to construct the transmission line.
The series resistance comes from the conductor used in the wires and from the conductor's geometry.The inductance and the capacitance derive from transmission line geometry, and the parallel conductance from the medium betweenthe wire pair. Note that all the circuit elements have values expressed by the product of a constant times a length; thisnotation represents that element values here have per-unit-length units. For example, the series resistance R ∼ has units of ohms/meter. For coaxial cable, the element values depend on the inner conductor's radius r i , the outer radius of the dielectric r d , the conductivity of the conductors σ , and the conductivity σ d , dielectric constant ε d , and magnetic permittivity μ d of the dielectric as
R ∼ 1 2 δ σ 1 r d 1 r i
C ∼ 2 ε d r d r i G ∼ 2 σ d r d r i L ∼ μ d 2 r d r i For twisted pair, having a separation d between the conductors that have conductivity σ and common radius r and that are immersed in a medium having dielectric and magnetic properties, the elementvalues are then
R ∼ 1 r δ σ
C ∼ ε d 2 r G ∼ σ d 2 r L ∼ μ δ 2 r d 2 r

Questions & Answers

Three charges q_{1}=+3\mu C, q_{2}=+6\mu C and q_{3}=+8\mu C are located at (2,0)m (0,0)m and (0,3) coordinates respectively. Find the magnitude and direction acted upon q_{2} by the two other charges.Draw the correct graphical illustration of the problem above showing the direction of all forces.
Kate Reply
To solve this problem, we need to first find the net force acting on charge q_{2}. The magnitude of the force exerted by q_{1} on q_{2} is given by F=\frac{kq_{1}q_{2}}{r^{2}} where k is the Coulomb constant, q_{1} and q_{2} are the charges of the particles, and r is the distance between them.
Muhammed
What is the direction and net electric force on q_{1}= 5µC located at (0,4)r due to charges q_{2}=7mu located at (0,0)m and q_{3}=3\mu C located at (4,0)m?
Kate Reply
what is the change in momentum of a body?
Eunice Reply
what is a capacitor?
Raymond Reply
Capacitor is a separation of opposite charges using an insulator of very small dimension between them. Capacitor is used for allowing an AC (alternating current) to pass while a DC (direct current) is blocked.
Gautam
A motor travelling at 72km/m on sighting a stop sign applying the breaks such that under constant deaccelerate in the meters of 50 metres what is the magnitude of the accelerate
Maria Reply
please solve
Sharon
8m/s²
Aishat
What is Thermodynamics
Muordit
velocity can be 72 km/h in question. 72 km/h=20 m/s, v^2=2.a.x , 20^2=2.a.50, a=4 m/s^2.
Mehmet
A boat travels due east at a speed of 40meter per seconds across a river flowing due south at 30meter per seconds. what is the resultant speed of the boat
Saheed Reply
50 m/s due south east
Someone
which has a higher temperature, 1cup of boiling water or 1teapot of boiling water which can transfer more heat 1cup of boiling water or 1 teapot of boiling water explain your . answer
Ramon Reply
I believe temperature being an intensive property does not change for any amount of boiling water whereas heat being an extensive property changes with amount/size of the system.
Someone
Scratch that
Someone
temperature for any amount of water to boil at ntp is 100⁰C (it is a state function and and intensive property) and it depends both will give same amount of heat because the surface available for heat transfer is greater in case of the kettle as well as the heat stored in it but if you talk.....
Someone
about the amount of heat stored in the system then in that case since the mass of water in the kettle is greater so more energy is required to raise the temperature b/c more molecules of water are present in the kettle
Someone
definitely of physics
Haryormhidey Reply
how many start and codon
Esrael Reply
what is field
Felix Reply
physics, biology and chemistry this is my Field
ALIYU
field is a region of space under the influence of some physical properties
Collete
what is ogarnic chemistry
WISDOM Reply
determine the slope giving that 3y+ 2x-14=0
WISDOM
Another formula for Acceleration
Belty Reply
a=v/t. a=f/m a
IHUMA
innocent
Adah
pratica A on solution of hydro chloric acid,B is a solution containing 0.5000 mole ofsodium chlorid per dm³,put A in the burret and titrate 20.00 or 25.00cm³ portion of B using melting orange as the indicator. record the deside of your burret tabulate the burret reading and calculate the average volume of acid used?
Nassze Reply
how do lnternal energy measures
Esrael
Two bodies attract each other electrically. Do they both have to be charged? Answer the same question if the bodies repel one another.
JALLAH Reply
No. According to Isac Newtons law. this two bodies maybe you and the wall beside you. Attracting depends on the mass och each body and distance between them.
Dlovan
Are you really asking if two bodies have to be charged to be influenced by Coulombs Law?
Robert
like charges repel while unlike charges atttact
Raymond
What is specific heat capacity
Destiny Reply
Specific heat capacity is a measure of the amount of energy required to raise the temperature of a substance by one degree Celsius (or Kelvin). It is measured in Joules per kilogram per degree Celsius (J/kg°C).
AI-Robot
specific heat capacity is the amount of energy needed to raise the temperature of a substance by one degree Celsius or kelvin
ROKEEB
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Source:  OpenStax, Fundamentals of electrical engineering i. OpenStax CNX. Aug 06, 2008 Download for free at http://legacy.cnx.org/content/col10040/1.9
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