1. Chapter 9. Analog Signals
第九章 類比訊號
亞洲大學
資訊工程學系碩士班
呂克明教授
二○○六年十二月四日
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2. Chapter 9. Analog Signals (第九章 類比訊號)
Introduction (緒言)
The Telephone Channel (電話頻道)
Single-Sideband Telephony (單旁帶話音技術)
FDM Telephony (頻分多工話音技術)
Color Television (彩色電視)
Homework Problems (習題)
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3. Introduction (緒言)
Analog signals are electrical replicas of the original signals such as audio and video.
Base band signals are those signals which occupy the lowest, or base, band of frequencies, in the frequency spectrum used by the telecommunication network.
A base band (基頻) signal may consist of one or more information signals.
Frequency-division multiplexing (頻分多工): For example, a number of analog telephony signals may be combined into one base band signal by the process known as frequency-division multiplexing.
Modulation (調變): In forming the multiplexed base band signals, the information signals are modulated onto sub-carriers.
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4. The Telephone Channel (電話頻道)
Natural speech (自然的語言聲音) covers a frequency range of about 80 to 8000 Hz.
Telephone quality (話音質量): The range of 300 to 3400 Hz is accepted internationally as the standard for telephony quality speech, and this is termed the speech base band.
The telephone channel is often referred to as a voice frequency (VF) channel.
In China #1 telephony signaling (中國一號訊令), a special in band frequency of 2300 Hz is used as a control signal.
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5. Single-Sideband Telephony (單旁帶話音技術)
When the telephone signal is multiplied in the time domain with a sinusoidal carrier of frequency Fc, a new spectrum results, in which the original base band appears on either side of the carrier frequency.
Double-Sideband: The band of frequency below the carrier as the lower sideband. The band of frequency above the carrier as the upper sideband.
To avoid distortion which would occur with sideband overlap, the carrier frequency must be greater than the highest frequency in the base band.
A filter may be used to select either one and reject the other. The resulting output is termed a single-sideband (SSB) signal.
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6. FDM Telephony (頻分多工話音技術)
Frequency-division multiplexing (FDM) provides a way of keeping a number of individual telephone signals separate while transmitting them simultaneously over a common transmission link circuit.
Each telephone base band signal is modulated onto a separate sub-carrier, and all the upper or all the lower sideband are combined to form the frequency-multiplexed signal.
Each voice channel occupies the range 300 to 3400 Hz, and each is modulated onto its own sub-carrier.
The sub-carrier frequency separation is 4 kHz, this allowing for the basic voice bandwidth of 3.1 kHz plus an adequate guard band for filtering.
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7. FDM Telephony (頻分多工話音技術)(continued)
CCITT (國際電信電話諮詢委員會, ITU-T ) modulation plan:
Group: 12 voice-frequency channels. Overall bandwidth of a group extends from 60 to 108 kHz.
Super Group: 60 VF-channel super group (SG) extending from 312 to 552 kHz.
Basic Master Group: 300 VF-channel basic master group extending from 812 to 2044 kHz. Allowing 8-kHz guard bands between sidebands. Basic master group consists of five (5) super groups together: SG1 ( kHz), SG2 ( kHz), SG3 ( kHz), SG4 ( kHz), and SG5 ( kHz) supper groups. The central carrier frequencies are 1364, 1612, 1860, 2108, and 2356 kHz, respectively.
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8. FDM Telephony (頻分多工話音技術)(continued)
CCITT modulation plan (continued):
Super Master Group: 900 VF-channel master super group extends from 8516 to kHz. Super master group consists of three (3) basic master groups (MG1, MG2, MG3). Allowing 88 kHz guard bands between sidebands. The central carrier frequencies of three (3) MG are 10,560, 11,880, and 13,200 kHz, respectively.
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9. Color Television (彩色電視)
The base band signal for television is a composite of the visual information signals and synchronization signals.
The visual information is transmitted as three (3) signal components, denoted as the Y, I, and Q signals.
The Y signal is a luminance, or intensity, component and is also the only visual information signal required by monochrome receivers.
The I and Q signals are termed chrominance components, and together they convey information on the hue or tint and on the amount of saturation of the coloring which is present.
The synchronization signal consists of narrow pulses at the end of each line scan for horizontal synchronization and a sequency (序列) of narrow and wider pulse at the end of each field scan for vertical synchronization.
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10. Homework Problems (習題)
9.1 State the frequency limits generally accepted for telephone transmission of speech. What is the reason behind? Please briefly describe.
9.10 Explain what is meant by frequency modulation.
9.26 Super Master Group: 900 VF-channel master super group extends from 8516 to kHz. Super master group consists of three (3) basic master groups. Allowing 88 kHz guard bands between sidebands. The carrier frequencies of three (3) MG are 10,560, 11,880, and 13,200 kHz, respectively. Please calculate three (3) basic sidebands.
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