Post on 26-Dec-2015
RADIO AND TELEVISION BROADCASTING
• AM Radio• FM Radio• Television
• AM Radio Broadcasting – 535-1605 kHz– 10 kHz carrier spacing– bandwidth of m(t) is 5kHz.– Superheterodyne receiver with intermediate frequency– two frequency components and are produced after
the mixer
3.4.1 AM Radio Broadcasting
kHz 455IFf
IFcLO fff
IFf IFc ff 2
• Rejection of the radio signal at the image frequency
• Assume there are two received signals
The mixer output consists of the two signals
• The RF amplifier bandwidth is designed to be sufficiently narrow so that the image frequency signal is rejected
• The IF amplifier has bandwidth of 10kHz to reject signal from adjacent channels.
IFLOc fff '
)2cos()](1[)(
)2cos()](1[)('
22
11
tftmAtr
tftmAtr
cc
cc
)2cos()](1[)(
)2cos()](1[)(
22
11
tftmAty
tftmAty
IFc
IFc
Desired signal
Interference from image channel
IFRF fB 2
• 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
3.4.2 FM Radio Broadcasting
MHz7.10IFf
IFcLO fff
kHzBW 200
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 DSB-SC 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
• 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.
3.4.3 Television Broadcasting
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 FM-modulated signal is selected as 25 kHz, and the FM-signal needs bandwidth of 70 kHz.
3.5 Mobile Radio Systems • 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.