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AM/FM Radios and Digital Television

AM stands for "amplitude modulation" - a type of signal. With AM, the amplitude of the combined audio frequency and radio frequency waves varies to match the audio signal. AM radio can develop problems with interference. This makes it hard to hear the radio show. Interference can be caused by many sources. For example, sparks discharge when a car is started, in electric motors in all sorts of electrical appliances, and even lightning. All of these things can produce interference to AM radio. As you can see, there is a lot of background noise that changes the amplitude of the radio wave signal. This creates the random crackling noises call static.

FM stands for "frequency modulation"- a type of radio transmission, the frequency of the combined waves change to reproduce the audio signal. For example, higher frequency is associated with the peak amplitude in the audio wave. FM waves do not have a problem with interference because the noise background does not modify the radio wave frequency. In addition, FM waves give better sound reproduction.

FM radio stations all transmit in a band between 88 megahertz (millions of cycles per second) and 108 megahertz. The band is divided into 100 channels, each 200 kHz (0.2 MHz) wide. The center frequency is located at 1/2 the bandwidth of the FM Channel, or 100 kHz (0.1 MHz) up from the lower end of the channel. For example, the center frequency for Channel 201 (the first FM channel) is 88.0 MHz + 0.1 MHz = 88.1 MHz. So there can be a station at 88.1 megahertz, 88.3 megahertz, 88.5 megahertz, and so on. The 200-kilohertz spacing, and the fact that they center on odd numbers is completely arbitrary and was decided by the FCC. In Europe, the FM stations are spaced 100 kilohertz apart instead of 200 kilohertz apart, and they can end on even or odd numbers.

Digital Television is a new system of bringing TV signals to your TV set. The DTV signals sent from TV stations are in digital modulation format rather than in the analog modulation format, which has been used since television began. You can see digital TV sets on sale at most electronics and large appliance stores right now. They are the ones with the wide screens similar in shape to the screen in a movie theater. Most of these DTV sets are still pretty expensive but the prices are coming down rapidly. DTV allows TV stations to provide you with new and different services that were not available with the old analog system. Probably the most important DTV service is the delivery to your home of High Definition TV (HDTV) signals. Pictures on a DTV set with an HDTV signal provide you with an unusually bright, clear, sharp and lifelike picture in a wide screen format with surround sound audio capability. All TV stations in the United States are supposed to be changing from the analog system to DTV by the end of 2006 but it may take longer than that. In the meantime, each TV stations is broadcasting both an analog signal and a DTV signal on different TV channels so you can receive ether one you want.

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Question 1
Which of the following is a type of radio transmission?
A. Signal modulationB. Radio modulation
C. Frequency modulationD. all of the above
Question 2
Which is NOT correct?
A. AM radio have problems with interference.B. FM waves have a problem with interference.
C. FM waves do not have a problem with interference.D. FM waves give better sound reproduction.
Question 3
What are the random crackling noises in the audio signal called?
A. WavesB. Kinetic
C. StaticD. Amplitude
Question 4
Radio stations that transmit on frequency modulation are called ________.
A. FM stationsB. AM stations
C. FMT stationsD. DTV stations
Question 5
How many channels is the FM radio transmission band divided into?
A. 88B. 100
C. 108D. 50
Question 6
What is the center frequency for Channel 201?
A. 80.1 MHzB. 78.1 MHz
C. 8.1 MHzD. 88.1 MHz
Question 7
What is the transmission band for FM radio stations?
A. 100 MHz and 208 MHzB. 88 MHz and 108 MHz
C. 88 MHz and 88.1 MHzD. 88.3 MHz and 88.5 MHz
Question 8
What is the frequency spacing between FM stations in Europe?
A. 200 kilohertzB. 100 megahertz
C. 88 megahertzD. 100 kilohertz
Question 9
Which format of the DTV signals are more popular in TV stations these days?
A. Analog modulation formatB. Binary modulation format
C. Digital modulation formatD. none of the above
Question 10
Why DTV is better than analog system?
A. because DTV provides High Definition TV signalsB. because DTV provides extremely bright and sharp picture quality
C. because DTV provides a wide screen format with surround sound audio capabilityD. all of the above
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