communication by safe hands

8/7/2019 Communication by safe hands

1/48

Safe Hands

By

Nitin OkeFor Safe Hands

The image cannot be displayed. Your computer may not have enoughmemory to open the image, or the image may have been corrupted.Restart your computer, and then open the file again. If the red x stillappears, you may have to delete the image and then insert it again.


2/48

Safe Hands

Communication

Faithful transfer of information fromone place to another is called ascommunication.

If communication is from A to B but not

from B to A then such communication iscalled as unilateral communication.

If it is two way then is called as bilateral

communication. There are large number of ways to

communicate.


3/48

Safe Hands

Different ways of Communication

Body gestures, Sound, Picture, language,symbol, Distant communication, tele-phone / vision

If communication is from A to B then A

has ( or is ) transformer B has (or is)receiver. The mode of transfer ofinformation is via cannel between

Transformer and receiver. We are more interested in distant

communication.


4/48

Safe Hands

Space/troposphericwaves

Distant communication

Space communication Line communication

GroundWaves

Sky/ ionospericWaves

Two wireCoaxial cableOptical fibre


5/48

Safe Hands

Electromagnetic waves

ExperimentalEHF30GHz to 300GHz

Radio relaySHF3GHz to 30GHz

TV/Radar/FMUHF300MHz to 3GHz

BroadcastingVHF30MHz to 300MHz

MarineSW/HF3MHz to 30MHz

Point to pointMW300KHz to 3MHz

Used forCalled asRange offrequency


6/48


7/48

Safe Hands

Atmosphere for communication purpose

D- Layer between 50 to 90 Km but appears during daytime only and less ionized.

E- Layer between 90 to 140 Km also called as KennlyHeaviside Layer also appears during day time only but can

be used for internal refraction of LF ( < 500KHz)

F- Layer between 140 to 400 Km which splits into twolayers as F1 ( 140 to 250Km) and F2 between (250 to 400km)F2 is called as Appleton Layer.


8/48

Safe Hands

Transmission by ground wave

Also called as surface wave Propagation by vertically polarized wave Large amount of power losses due to

induced current, diffraction effect.

(Attenuation) Covers very less distance of the order of

1500Km

Uses frequency below 500KHz Amplitude modulated radio waves aretransmitted by ground waves.


9/48

Safe Hands


10/48

Safe Hands

Transmission by space waves

Also called as direct wave or Tropospheric

wave or line of sight wave. Propagation by direct or reflected waves from

troposphere or from ground.

May have constructive or destructiveinterference. Called as selective fading.

If h is height of antenna then can cover atmost 2hR distance.( Why?)

It is for frequencies above 30MHz. To increase range either increase height or use

repeater transmitting stations.


11/48

Safe Hands

R2 +(h2+d2)=(R+h)2

d2=2Rh


12/48

Safe Hands


13/48

Safe Hands

Sky wave propagation

Also called as ionospheric propagation. Propagation by direct or reflected waves

from ionosphere or troposphere or fromground.

Sky wave propagation is most unreliabletransmission. This is because the skywave reflects from F layer whoseexistence and density changes time to

time. All wave above 30MHz do not reflect

even by ionosphere and go into space.


14/48

Safe Hands

Skip distanceSkip Zone

Ground wave range


15/48

Safe Hands

Satellite communication

When range of frequency is above 30MHz

previously discussed modes are useless. To provide communication for longer distances atlow cost the method of satellite communication isused.

The concept was initially discussed by an author

Arther CClark in a science fiction wireless world This is an effective way of creating an antenna of

height of the order of 35939Km(36000km) To avoid weakening of signal during to and fro

journey of uplink and downlink signal received is

amplified before sending back, to avoidinterference between uplink and downlink thefrequencies are different ( 6GHz and 4GHz)

The unit performing all above task is called asTransponder


16/48

Safe Hands

Concept of satellite communication


17/48

Safe Hands

Merits and demerits of satellite communication

Wide area of broadcast

Quality is identical and good

Economical

More cost effective in hilly area Used for global positioning up to 100km

Provides link for complete earth.

Threat for security and privacy. Not possible to correct

Time delay due to a gap of 2 x 36000 km


18/48

Safe Hands

Byproduct of communication- Remote sensing

Is the science of obtaining informationabout an object when it is not directly incontact with the investigator.

Description, sketch, Painting, Photograph

are few examples of remote sensing. The satellite which does a job of justtaking a photograph and sending it toearth is called as passive satellite.

The satellite which process the signal asper need and then sends back is called asactive satellite.


19/48

Safe Hands


20/48

Safe Hands

Active or passive satellites

As satellites used for communication maybe used for remote sensing but they arefar away from earth.

For remote sensing satellites used are

suppose to come close to earth so needtheir orbit elliptic and instead of theymoving to scan if earth moves it will save

energy. Thus these satellites are preferred with

tilt to equator up to 63o


21/48

Safe Hands

Structure of satellite used for RS

11.56o

168 to 188km

Altitudewhenphotographsare taken is918 to

1000Km


22/48

Safe Hands

Basic terminology

Transducer: Any device that convertsone form of energy into another can betermed as a transducer. An electricaltransducer may be defined as a device

that converts some physical variable(pressure, displacement, force,temperature, etc) into corresponding

variations in the electrical signal at itsoutput.


23/48

Safe Hands

Signal: Information converted in electrical

form and suitable for transmission is called asignal.

Signals can be either analogor digital.

Analog signals are continuous variations ofvoltage or current. They are essentially single-valued functions of time. Sine wave is afundamental analog signal. All other analog

signals can be fully understood in terms oftheir sine wave components. Sound and picturesignals in TV are analog in nature.

Basic terminology


24/48

Safe Hands

Digital signals are those which can takeonly discrete stepwise values. Theyemploy suitable combinations of numbersystems such as the binary coded decimal

(BCD) American Standard Code forInformation Interchange (ASCII)

Noise: Noise refers to the unwanted

signals that tend to disturb thetransmission and processing of messagesignals in a communication system.

Basic terminology


25/48

Safe Hands

Transmitter: A transmitter processesthe incoming message signal so as tomake it suitable for transmission througha channel and subsequent reception.

Receiver: A receiver extracts thedesired message signals from thereceived signals at the channel output.

Attenuation: The loss of strength of asignal while propagating through amedium is known as attenuation.

Basic terminology


26/48

Safe Hands

Basic terminology

Amplification: It is the process of increasing

the amplitude (and consequently the strength)of a signal using an electronic circuit called theamplifier. Amplification is done at a placebetween the source and the destination

wherever signal strength becomes weaker thanthe required strength.

Range: It is the largest distance between a

source and a destination up to which the signalis received with sufficient strength.


27/48

Safe Hands

Basic terminology

Bandwidth: Bandwidth refers to the frequency range

over which an equipment operates or the portion of thespectrum occupied by the signal. Modulation: The original low frequency

message/information signal cannot be transmitted tolong distances due to low frequency. The low frequency

message signal is superimposed on a high frequencywave, which acts as a carrier of the information. Thisprocess is known as modulation.

There are three types of modulation AM, FM and PM. Demodulation: The process of retrieval of information

from the carrier wave at the receiver is termeddemodulation. This is the reverse process ofmodulation.


28/48

Safe Hands


29/48

Safe Hands

Need of modulation

For transmitting a signal, we need an antenna

or an aerial. This antennashould have a size comparable to thewavelength of the signal (at least P/4 indimension) for sound wave of frequency 20kHz, the wavelength P is 15 km. ( if velocity is

that of EM wave.) Obviously, such a longantenna is not possible to construct andoperate.

We can obtain transmission with reasonableantenna lengths if transmission frequency ishigh (for example, if Y is 1 MHz, thenP is 300 m).


30/48

Safe Hands

Need of modulation

A theoretical study of radiation from a linear

antenna (length L) shows that the powerradiated is proportional to (L/ P)2 .

The above arguments suggest that there is aneed for translating the original low frequency

information signal into high frequency wavebefore transmission such that the translatedsignal continues to possess the informationcontained in the original signal. In doing so, we

take the help of a high frequency signal, knownas the carrier wave, and a process known as modulation


31/48

Safe Hands

Need of modulation

For transmitting a signal, we need an antenna

or an aerial. This antennashould have a size comparable to thewavelength of the signal (at least P/4 indimension) for sound wave of frequency 20kHz, the wavelength P is 15 km. ( if velocity is

that of EM wave.) Obviously, such a longantenna is not possible to construct andoperate.

We can obtain transmission with reasonableantenna lengths if transmission frequency ishigh (for example, if Y is 1 MHz, thenP is 300 m).


32/48

Safe Hands

Different types of modulations

P E N


33/48

Safe Hands

AMPLITUDE MODULATION

Let c(t) = Ac sin ct represent carrier wave

m(t) = Am sin mt represent the message signal The modulated signal cm (t) can be written as

cm (t) = (Ac + Am sin mt) sin ct

Here = Am/Ac is the modulation index


34/48

Safe Hands


35/48

Safe Hands


36/48

Safe Hands


37/48

Safe Hands


38/48

Safe Hands


39/48

Safe Hands


40/48

Safe Hands


41/48

Safe Hands

Applications of remote sensing

Meteorology: weather modeling and forecasting

Oceanography: sea surface scan, oil spills,mapping of polar ice caps, understanding underwater currents.

Irrigation monitoring, pre flood and post flood

river configuration Ground water zones Land survey Military espionage and civil purpose Environment: costal study, industrial waste,

pollution.


42/48

Safe Hands

Wire communication

Parallel

wire line

Twisted

wire line

Coaxial

wire line

Optical

fiber line


43/48

Safe Hands

Wire communication

Two wire communication :

Parallel wire line: Line consist of two insulated copper wiresparallel to each other along their length. In this line twowires form a LCR circuit as shown in following figure

To reduce power losses the impedance must be matchedwith load resistance and it has to be changed as frequencychanges.

Resistance appears because of leakage of current throughskin of wire

If frequency increases then inductive reactance increases

results into power loss. So the line is called as balance line.

bb


44/48

Safe Hands

Wire communication

Two wire communication : Twisted wire line : Line consist of two insulated

copper wires twisted around each other alongtheir length.

D

ue to twist the inductive effect is reducedand power losses are reduced. The frequencycan not have much effect on power transferhence the line is called as unbalanced line


45/48

Safe Hands

Wire communication

Two wire communication :

Coaxial line : Line consist of copper wire insulatedby PVC and surrounded by a copper mesh whichagain is insulated.


46/48

Safe Hands

Construction of coaxial cable

It consist of inner conductor of copper

wire which is held on by insulatingmaterial like teflon or polyethelene. Theouter layer is made up of copper meshand generally earthed. At the end it hascoating, due to outer copper shield theline is saved from external electric andmagnetic fields. The line can used till20MHz signals but beyond this frequencyinductive reactance reduces powerdrastically.


47/48

Safe Hands

Optical Communication

Optical fiber is made up of three parts

Core: A cylinder of diameter of order 10 to100 micro meter which is made up of glass with100% transmission. Refractive index is Q1

Cladding: it surrounds core made up of

transparent material of refractive index Q2which is less than Q1. The refractive index canof cladding may change abruptly (a step indexfiber) or gradually (graded index fiber)

Buffer: A plastic coating to support cladding isoutermost part also called as housingencapsulates.


48/48

Safe Hands

Optical fiber

Mono modeoptical fiber

Step index

Multi modeoptical fiber

Graded index

Multi modeoptical fiber

5Qm

125Qm

50Qm

125Qm

50Qm

communication by safe hands

Documents