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On the transmitter side, the digital I and Q data – which are already processed by a digital-to-analog converter, filtered and amplified – are up-converted by quadrature mixers to the carrier frequency of interest. After combining, the signal is again filtered to contain the spectral content of the signal in the required bandwidth stipulated by the emission mask. After that, it is applied to the power amplifier and transmitted over the air with an antenna (Figure 2).

Now let's get into the details for each of the blocks in the transmitter and receiver.

Antennas

Antennas are coupling circuits to space that radiate or receive information-bearing electromagnetic waves. In a receiving antenna, the EM wave impinging on the surface produces currents, which in a 50-ohm system are applied to an LNA for amplification and subsequent processing. On the transmitter side, the surface current density on the antenna produces a magnetic field around the antenna. If the current density is time-varying, an accompanying electric field is also produced; propagation takes place in a direction perpendicular to both the electric and magnetic fields. The total radiated power is given by a surface integral of the Poynting vector over any surrounding surface. The value of resistance that would dissipate this amount of power is called the radiation resistance, which is caused by the power radiated. The total resistance of the antenna comprises radiation resistance and resistance due to power loss. For high efficiency, the value of radiation resistance should be large.

Filters

Filters remove the effect of broadband noise and thereby increase the SNR of a desired signal. They are also used to select channels in multiple transmission environments and to remove image frequencies in broadband services and other out-of-band interference. In the transmitter, digital pulse-shaping filters are used for efficient utilization of the RF spectrum and externally to suppress RF splatter in adjacent channels.

Amplifiers

The RF signal at a receiver’s antenna is very small in magnitude. The IEEE 802.15.4 standard defines a minimum signal of -85 dBm = 3.16 pW, whose voltage in a 50-ohm system is 12.6 µV. At the detector, the typical signal requirement is at 1 mVp-p for detection and decoding of digital waveforms. To achieve this, low-noise amplifiers are used in the front end to amplify the signal up to the detection stage. The gain required in the receiver is usually between 60-90 dB – very high. Therefore, to avoid oscillations, this gain is distributed over different stages of the radio-frequency integrated circuit.

On the transmitter side, power amplifiers (PAs) are used to transmit the EM wave. PAs come in various classes and can be linear and nonlinear. They usually employ matching circuits between the output and the load. In practice, the output impedance of the active device is complex and varies with load; thus nonlinear complex impedance must be matched to a linear load. More often, the antenna impedance may be complex and vary with both the position of the transceiver and surrounding objects. This makes PA input and output matching a nontrivial task. In practice, a technique called load pull is applied to a matching circuit design. In this test, the output power is measured and plotted as a function of the complex impedance load seen by the transistor output stage. A tuner can accurately vary the output impedance while a power meter measures the power, keeping it constant. The impedance gives a contour on the Smith chart. As the output impedance varies, this changes the input impedance of the transistor, thus requiring the use of a second tuner such that the impedance seen by the generator remains constant.

Questions & Answers

Black market what is the meaning
Bless Reply
where there is illegal transactions of goods or services. where there illegal goods or services are sold.
Azhar
Scarcity is the major problem of any economy which is the limited resources an economy has in order to produce its country's unlimited wants/needs. Therefore, scarcity is the key term beyond the study of Economics.
Bature Reply
what is supply
Rahul Reply
Like the demand, the supply demonstrates the quantities that will be  sold at a certain price. But unlike the demand, the supply relationship  shows an upward slope. This means that the higher the price, the higher the  quantity supplied.  Producers supply more at a higher
Nazneen
or we can say that By supply we mean various quantatirs of a commodity which a producer will offer for sale at different possible prices over a given period of time
Nazneen
What is scarcity?
Jubille Reply
having unlimited needs and wants in a world of limited resources
William
what are the indicator of over population
Accorobatic Reply
Inefficiency of natural resources
Adekunle
Low PCI .
abhinav
resources are limited and wants are unlimited
Nazneen
limited resources
Nazneen
what product market?
Gayflor Reply
explain demand
Bless Reply
what is economics
Murali
Economics is the social science that studies the production, distribution and consumption of goods and services.Economics focuses on the behaviour and interactions of economic agents and how economies work.
Preeti
ok
SAGAR
Pls what is national income?
Ishmael
demand is the number of buyers. as the price of goods is increase, the buyers will not consider to buy the goods, so the demand will decreases
Pung
National Income is the aggregate monetary value of all final goods and services produced in an economy in an year .
abhinav
Why pecularities of land has no economic significance, What the economic bad, effictive demand?
James
Demand is a quantity of goods that a consumer is willing to buy at different prices over a given period of time
Nazneen
Define law of demand
Nazneen
what is deadweightloss
francis Reply
hi
Bless
deadweight loss is the allocative inefficiency.... when the equilibrium for good or services is not achived.
Azhar
hi
Azhar
hi
azaloo
hii too
Jackson
Hello
Micah
how are you all?
Azhar
I am here been sick but here
Amanda
may you get well soon Amanda
Azhar
What are the implications of classical Economics?
Micah
What are the implications of classical Economics school of thought?
Micah
Dead weight loss is an inefficient allocation of resources, especially through taxation or restrictions.
Ezeigwe
Classical Economics had an influenced by ancient economic principle and theory.
Ezeigwe
yec
Yasinta
nice
Amanda
hello please what is localization of industry
Bless Reply
price is tantalisingly the only factor determining demand which can be analyze the view
Sinit Reply
Price is tantalizingly the only factor determining demand which can be analyze the view
Sinit
what is scarcity
Sharkdanny Reply
the state of being scarce or in short supply; shortage.
Abdirahin
what is meant by an abnormal demand curve?
Samuel Reply
what is microeconomics
Berun Reply
micronomics can be define as that part of Economics that deals with small scale business. e.g. House hold stuff
Amodu
Micro economics is the study of individuals, households and firms' behavior un decision making and allocation of resources
Christian
what is underemployment
Xornam Reply
It is the situation where the available resources are not used to it optimum
Bless
state the law of diminishing returns
Bless
Bless, the law of diminishing returns state that one point, adding a single worker will result in a decrease of production.
David
it is a situation where by people are employ but work under their potential
Akua
David please go into details kk
Bless
Akua pls when you say people alone? what about facilities?
Bless
Definition of underemployment. 1 : the condition in which people in a labor force are employed at less than full-time or regular jobs or at jobs inadequate with respect to their training or economic needs
Boahen
OK that is good
Set
I am new here
Taimoor
what does law of demand says?
Samuel
with a diagram explain fairy elastic demand
Samuel
comprehensive answer for public finance is the money that a government has available to spend from taxes and borrowing.
wilflay Reply
what then comprises of public opinion
Raphael
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
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Source:  OpenStax, Senior project guide to texas instruments components. OpenStax CNX. Feb 12, 2013 Download for free at http://cnx.org/content/col11449/1.3
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