RADIO AND TELEVISION BROADCASTING • AM Radio • FM Radio • Television
3.4.1 AM Radio Broadcasting • 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
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. Desired signal Interference from image channel
3.4.2 FM Radio Broadcasting • 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
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.
3.4.3 Television Broadcasting • 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.
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.