TV antenna booster

Introduction:

The Communication simply is the method of conveying information from one person or place to another .

This information converted to a signal .

The word “Signal” is derived from the Latin word “signum”, meaning a mark or sign .

Introduction

The first well-known satisfactory antenna experiment was conducted by the German physicist Heinrich Rudolf Hertz (1857–1894), in1887 he built a system.

television antenna or TV aerial, is an antenna specifically designed for the reception of over-the-air broadcast television signals.

TV bands has two bands : VHF ( 41-250)MHZ & UHF (470-960)MHZ

Introduction to TV:

The aim of a television system is to extend the sense of sight beyond its natural limits and to transmit sound associated with the scene .

the picture signal is amplitude modulated and sound signal frequency modulated before transmission.

each television station is allotted different carrier frequency to enable selection of desired station at the receiving end.

The TV receiver has tuned circuits in its input section called "tuner".

Introduction to TV:

The amplified IF signals are detected to obtain video, picture and audio sound signal.

there are two types of TV:

Analog Television:refers to a video display device that is similar to that used in standard radio transmissions.Analog TV transmissions are subject to interference, such as ghosting and snow.

Digital television (DTV): is a new television service representing the most significant development in television technology.

Introductionto TV :

converting of the analog signal to digital signal requiring three important(PCM):

Sampling :is the reduction of a continues signal to a discrete signal

Quantization: is the process of mapping a large set of input values to a smaller set.

Coding :Designating each quantized level by a (binary) code.

Introduction to TV:

A digital signal can be compressed far more than an analog signal.

digital signals get weaker with distance, just as analog signals do.

digital signals won't degrade in quality with in distance.

Digital signals can be broadcast in two ways:

over the airwaves:requiring new transmission tower or DTV antenna on existing tower.

delivering by a prerecorded source such as a digital video disc (DVD)

Introduction to TV:

Wave propagation: In 1864 Maxwell discovered that the time varying electric and magnetic fields together gives rise to an electromagnetic wave traveling in the radio waves.

EM signals when traveling through wireless channels experience fading effects due to various effects ,free space model predicting those effects by this eq.:

Introduction to TV:

Wave propagation can follow three basic paths according to their frequency: Sky wave :

Introduction to TV:

Ground-wave propagation (surface wave): travels along the earth surface Vertically polarized

stronger in the Low and Medium frequency ranges (LF, 30-300 kHz),(MF,300-3000 kHz)

low frequency signals (ELF, 30-300 Hz) were used to communicate

with submarines

Introduction to TV: Space wave propagation :

The technique of space wave propagation is used in bands having very high frequencies. E.g. V.H.F. band, U.H.F band etc.

These waves are limited to the curvature of the earth.

These waves have line of sight propagation, means their propagation is along the line of sight distance.

Introduction to TV:

Propagation of radio wave through ionosphere :

The sky wave propagation or ionosphere wave propagation is important as it assists global short wave communication

The layers which exist permanently act as a radio mirror to bounce back the sky wave to the earth. The waves which return back to the earth appear to be the waves reflected by the layers of the ionosphere .

Introduction to TV:

We have two types of TV antenna:

Outdoor antenna : ( yagi-uda, log-periodic) antenna

Indoor antenna : ( loop & rabbit ears ) antenna

Introduction to TV: Yagi-uda(super directive or super gain)antenna:The yagi-

uda antenna with three elements including one reflector, one driven element and one director is commonly called beam antenna .

It is generally a fixed frequency operated unit The bandwidth of 2 % to 3% can be easily achieved if the spacing

between the elements is between 0.1 to 0.5 .ƛ ƛ gain is about 7 to 8 dB, front to back ratio is 20 dB. unidirectional with a moderate directivity. Having low weight&cost and simple in feeding with signal

provides high gain and beam width

Introduction to TV:

Log-periodic antenna :periodic antenna is a broad band

antenna.

typical log periodic dipole array consist number of dipole of different

lengths and spacing.

Introduction to TV:

Indoor antenna : is a type of those antenna that placed indoors. High radiation resistance provided multi-turn ferrite-core

constructions are used.

High losses, therefore, low radiation efficiency.

Simple construction, small size and weight.

Reason behind signal weaknesses

What can cause disruption to my television reception?

There are a large number of possible sources of this, but usually the problem occurs when a nearby transmitter is operating outside of its permitted channel or a device unintentionally emits a signal within the television band. Disruption can also be caused by abnormal atmospheric and weather conditions; such disruption will only last while the conditions persist

Reason behind signal weaknesses:

EMI (Electromagnetic interferences): FROM ELECTRICAL SOURCES: Many electrical devices, such as electrical motors, tools and

appliances, can cause interference.

This sporadic interference generally occurs when an electrical

accessory or appliance starts up or is operating.



The interference may come from electrical power lines. The power grid that supplies your neighborhood is often a source of interference.


If your equipment is not picking up the desired signals clearly enough, or if it is picking up unwanted signals, interference

problems will appear. When the television receives two different signals at the same time,

there may be interference


Interference caused by an FM radio station


Interference caused by a radio transmitter :When this type of interference appears on the screen, or when voices can be heard.

This phenomenon generally affects VHF channels .


ghosting :is a replica of the transmitted image, offset in position, that is super-imposed on top of the main image.


The signal arrives at RX by means of two different paths which have different lengths. The main path is the direct path, while the second

is due to a reflection from the plane.


Distance:weak signal appears when you are too far from the transmitter of the station you want to pick up or when there are obstacles between the antenna and the transmitter. The effect will be the same if the antenna is faulty or is not pointed in the right direction.

The television picture is much more likely to be affected than the sound.


Signal overloading Are the situations where one or more of the TV signals reaching

your set from the antenna are simply too strong.


The Solutions for the signal weakness:


Distance: we need to install new towers

Increase the transmitting power Use antenna with higher gain at both

sides alternative solution for the problems

are using Booster


Engineering

TV antenna booster