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(Television Technology)
a. You need to review scanning (progressive and interlaced)
b. You need to review the analogue video interfacing techniques discuss the scope
of usage for each
c. Calculate the bandwidth requirements of the following television system.
(1024 scanning lines, 60 frames per second, 100 vertical blanking lines, interlaced
scanning)
d. Sketch block diagram of a typical Television production studio; explain the
function of each block
e. Sketch the composite video signal for a standard colour bar test signal.
f. Define the parameters for the progressive scan PAL DV format.
a. Calculate the bitrate for the uncompressed PAL DV format
b. Calculate the required compression ratio for storing one hour of PAL DV
video on a single layer DVD
The PAL DV parameters are:
720 x 576 = DV Pal frame size, 24 bit = colour depth (as 3 x r,g,b)
50 = frames per sec
The bit rate equals: total number of pixels * colour depth * frame rate
720 x 576 x 24 x 50 = 497,664,000 bits or 0.5 Gbits
Time = 1 hour or 3600 seconds (60 x 60),
3600 x 0.5 = 1800 Gbits
4.7 x 8 = 37.6 G bits. (Capacity of a single layer DVD)
1800/37.5 = 47.8
Ratio is 47.8
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(AM Broadcasting)
An AM broadcasting station has a licensed carrier power of 10 KW, the carrier
frequency is 1500 KHz and the modulation index is 0.8 when modulated by a single
tone 5 kHz audio signal. The transmitter is tested using a dummy load of 100 Ohms.
a. Calculate the total modulated signal power.
b. Calculate the carrier power and sidebands power.
c. Calculate the efficiency of the transmitter.
d. Calculate the maximum permissible output power of the station transmitter.
e. Calculate the carrier amplitude.
f. Calculate the audio tone amplitude.
g. Sketch the carrier signal, modulating signal and modulated signal in time domain.
h. Sketch the spectrum of the carrier signal, modulating signal and modulated
signal.
i. Calculate the Bandwidth of each signal?
Solution:
The Total power of AM DSB-TC is calculated using the following formula
(you must remember this formula)
Pt = Pc (1+m2/2)
The transmitter licensed carrier power (Pc = 10000 W)
10000*(1+0.82/2)
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Pc=10000W
The side bands power (Psb)
Psb= Pc* m2/2
Efficiency is the useful power (Psb) divided by the total power (Pt)
Efficiency = Psb/Pt = (m2/2) / (1+ m2/2)
PtMax is when m=1
Pt = Pc (1+m2/2)
The carrier is a sinusoidal wave and hence:
Pc = Ac2/2R
(where AC is the carrier amplitude and R is the antenna resistance or the
dummy load)
Ac2 = Pc * 2R
Ac = sqrt(Pc * 2R)
m = Am/Ac (modulation index )
Am = m * Ac
Carrier and modulating frequency are single tones.
For the modulated signal Bw= 2*fm = 10 KHz
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(FM Broadcasting)
An FM broadcasting station is modulated with a 5 KHz audio signal. The carrier
amplitude is 2000 volts and the carrier frequency is 100 MHz. The frequency
modulation index equals 2 and the antenna resistance = 100 Ohms.
a. Calculate the transmitter power dissipated in the dummy load.
b. Sketch the spectrum of the FM modulated signal.
c. Calculate the bandwidth of the modulated signal.
d. Sketch the block diagram of a Stereo FM transmitter. Explain the function of
each block.
e. Sketch the spectrum of a typical stereo FM broadcast channel.
Solution:
In FM the total power = the unmodulated carrier power, and it is constant
regardless of the modulation index or the audio amplitude.
Pt = Ac2/2R
Use the Bessel function Table to look up the values of the spectral components.
Plot them and note the index of the last value. You will see it is J4 and hence n=4
B.W= 2*n*fm
From Bessel function table: BW = 2* 4*5= 40 KHz
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Revision
Bessel function table for calculating FM spectrum
Spectrum of commercial FM
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Commercial FM Transmitter
Please solve all the tutorial problems that we went through in class
(These can be found on the course web page)