An introduction to frequency and amplitude modulation.
Especially for wireless channels, like commercial radio and
television, but also for wireline systems like cable television,an analog message signal must be
modulated : The
transmitted signal's spectrum occurs at much higher frequenciesthan those occupied by the signal.
We use analog communication techniques for analog message
signals, like music, speech, and television. Transmission andreception of analog signals using analog results in an
inherently noisy received signal (assuming the channel addsnoise, which it almost certainly does).
The key idea of modulation is to affect the amplitude, frequency
or phase of what is known as the
carrier sinusoid. Frequency modulation (FM) and less frequently used
phase modulation (PM) are not discussed here; we focus onamplitude modulation (AM). The amplitude modulated message
signal has the form
where
is the
carrier frequency and
the
carrier amplitude . Also, the signal's
amplitude is assumed to be less than one:
. From our previous exposure to amplitude modulation
(see the
Fourier Transform example ), we know that the
transmitted signal's spectrum occupies the frequency range
, assuming the signal's bandwidth is
Hz (see the
figure ). The carrier
frequency is usually much larger than the signal's highestfrequency:
, which means that the transmitter antenna and carrier
frequency are chosen jointly during the design process.
The AM coherent receiver along with the spectra of key
signals is shown for the case of a triangular-shaped signalspectrum. The dashed line indicates the white noise level. Note that
the filters' characteristics — cutoff frequency andcenter frequency for the bandpass filter — must be match to
the modulation and message parameters.
Ignoring the attenuation and noise introduced by the channel for
the moment, reception of an amplitude modulated signal is quiteeasy (see
[link] ).
The so-called
coherent receiver multiplies the
input signal by a sinusoid and lowpass-filters the result (
[link] ).
Because of our trigonometric identities, we know that
At this point, the message signal is multiplied by a constant
and a sinusoid at twice the carrier frequency. Multiplication bythe constant term returns the message signal to baseband (where
we want it to be!) while multiplication by the double-frequencyterm yields a very high frequency signal. The lowpass filter
removes this high-frequency signal, leaving only the basebandsignal. Thus, the received signal is
This derivation relies solely on the time domain; derive the
same result in the frequency domain. You won't need thetrigonometric identity with this approach.
The signal-related portion of the transmitted spectrum is
given by
.
Multiplying at the receiver by the carrier shifts thisspectrum to
and to
, and scales the result by half.
The signal components centered at twice the carrier frequency
are removed by the lowpass filter, while the baseband signal
emerges.
Because it is so easy to remove the constant term by electrical
means—we insert a capacitor in series with the receiver'soutput—we typically ignore it and concentrate on the signal
portion of the receiver's output when calculatingsignal-to-noise ratio.
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.
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?
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
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
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
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
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?
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?
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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