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題名 | 550MHz有線電視系統下行頻段單一波道視頻載波振幅與頻率之抽取量測=Extraction and Measurement of In-Channel Visual Carrier Amplitude and Frequency in the Down Strean for a 550MHZ Cable Television System |
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作者姓名(中文) | 洪鴻文; | 書刊名 | 技術學刊 |
卷期 | 14:4 1999.12[民88.12] |
頁次 | 頁511-518 |
分類號 | 448.88 |
關鍵詞 | 移頻處理; 頻率計值相對觀測; 振幅計值範圍比對; Frequency shifting conversion; The Relative observation of frequency counting; The range comparison of amplitude counting; |
語文 | 中文(Chinese) |
中文摘要 | 「有線電視系統用戶終端信號品質查驗」參數群中下行頻段單一波道視頻載波振 幅與頻率值之量測,一般均使用頻譜分析法測量,屬於通頻帶(頻域)技術,架構較複雜且 實踐困難度較高,本文中提出之量測架構則具有簡單易實踐之特性,在載波頻率值抽取量測 方面, 利用移頻技巧將下行頻段中欲量測之單一波道信號皆移頻至 CH3 (該波道之單一波 道視頻載波位置 61.25MHz )再以計頻器觀測載波頻率是否皆在相對位置( 61.25 MHz ) 處,載波振幅值之抽取量測則採範圍值判斷方式,不去抽取量測振幅真正值大小,因為一來 實際量測振幅真值不僅存在誤差問題亦會造成量測架構複雜化,二來根據「有線電視系統用 戶終端信號品質查驗規範」明定用戶終端單一波道視頻載波振幅值必須在 0 ∼ 14dBV 範圍 之內, 基於上述考量,故採直接在通頻帶抽取視頻載波振幅強弱,並利用單晶片 89C51 處 理技術完成比較判斷與顯示功能,將抽取量測結果以範圍值表示。 |
英文摘要 | In the measurement of signal quality at the subscribers of a cable television (CATV) system, the amplitude and frequency of an in-channel visual carrier in the down stream are important parameters. In general, those parameters are measured by means of spectral analysis which is a kind of passband technique in the frequency domain. The spectral analysis method is complex and difficult to implement. In this paper we propose a new measurement architecture to extract and measure the frequency and amplitude of an in-channel visual carrier directly. The proposed architecture is simple and easy to implement. In the extraction of amplitude and frequency froman in channel visual carrier, the signals in the down stream are first converted and shifted to CH3,in which the carrier frequency is 61.25MHz. Then we can verify the position of in-channel visual carrier by means of a frequency counter. In addition, the measurement of amplitude of in-channel visual carrier is in terms of its range rather than its actual value. This is because that measurements with high precision always make the underlying architecture more complex. Moreover, the visual carrier level shoul be specified in a range of 0 ∼ 14dBmV rather than a fixed value. Base upon above consideration, the single-chip microprocessor (89C51) technique is used to simplify and implement the proposed measurement architecture. |
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