Transcript RADIO AND TELEVISION BROADCASTING

RADIO AND TELEVISION BROADCASTING
• AM Radio
• FM Radio
• Television
3.4.1 AM Radio Broadcasting
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AM Radio Broadcasting
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535-1605 kHz
10 kHz carrier spacing
bandwidth of m(t) is 5kHz.
Superheterodyne receiver with intermediate frequencyf  455kHz
IF
two frequency components f and 2 f  f are produced after
IF
c
IF
the mixer
f LO  f c  f IF
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Rejection of the radio signal at the image frequency
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'
f
f
c  f LO
Assume there are two received
signalsIF
r1 (t )  Ac [1  m1 (t )]cos(2f ct )
The mixer output consists of the two signals
r2 (t )  Ac [1  m2 (t )]cos(2f c't )
Desired signal
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y1 (t )  Acis[1designed
 m1 (t )]
2f IF t ) narrowInterference
The RF amplifier bandwidth
tocos(
be sufficiently
so that the
image frequency signal
from image
y2 (t ) isrejected
Ac [1  m2 (t )]cos(2f IF t )
channel
The IF amplifier has bandwidth of 10kHz to reject signal from adjacent
channels.
BRF  2 f IF
3.4.2 FM Radio Broadcasting
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FM Radio Broadcasting
– for transmission of voice and music signals (bandwidth of m(t) is
15 kHz)
– 88 - 108 MHz
– 200 kHz carrier spacing
– peak-frequency deviation 75 kHz
– Superheterodyne receiver with intermediate frequency
f IF  10.7 MHz
BW  200 kHz
f LO  f c  f IF
FM-Stereo Broadcasting
• Many FM-stereo stations transmit music programs in
stereo by using the outputs of two microphones.
• A pilot tone at the frequency of 19 kHz is added to
the signal for the purpose of demodulating the DSBSC AM signal.
• A monophonic FM receiver can recover the summed
signal L+R by using a conventional FM demodulator.
Hence, the FM-stereo broadcasting is compatible
with the conventional FM.
FM Stereo Transmitter
FM Stereo Receiver
3.4.3 Television Broadcasting
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Commercial TV broadcasting began as black-and-white picture transmission
by BBC in 1936.
The two dimensional image is converted to a one-dimensional electrical signal
by sequentially scanning the image.
The scanning of the electron beam in the CRT is controlled by two voltage
applied across the horizontal and vertical deflection plates.
In commercial TV broadcasting, the bandwidth of the video signal is is limited
to W = 4.2 Mhz.
VSB modulation is employed, the total transmission bandwidth is around 6
Mhz.
Interlaced pattern with rate 1/60 sec
A typical video signal
• The audio portion of the TV signal is
transmitted is limited to W= 10 kHz.
• The peak frequency deviation in the FMmodulated signal is selected as 25 kHz, and
the FM-signal needs bandwidth of 70 kHz.
3.5 Mobile Radio Systems
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Cellular concept
Terminologies
• The simultaneous transmission between two
parties is called full-duplex operation.
• In analog cellular system, the 3 kHz audio
signal is transmitted via FM using a channel
bandwidth of 30 kHz. This represents a
bandwidth expansion of approximately a
factor of 10.