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題名 | 調幅光纖有線電視電路的CNR=The Carrier to Noise Ratio (CNR) in an AM Optical Fiber CATV Link |
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作者 | 劉時淼; | 書刊名 | 中華電信技術季刊 |
卷期 | 2:2 1998.05[民87.05] |
頁次 | 頁113-119 |
分類號 | 448.88 |
關鍵詞 | 調幅光纖; 有線電視電路; 載波雜訊比; CNR; |
語文 | 中文(Chinese) |
中文摘要 | 由於光纖具有低損失、不受電磁干擾、耐用、好維護的特性,有線電視業者為提 昇競爭力,以混合式光纖與同軸電纜網路取代原有的同軸電路。載波雜訊比(CNR)是有線電視 的重要參數之一,而且與光纖線路施工有著密切的關係,在光收、發訊機都合乎標準的條件 下,線路品質之良窳,CNR是一重要因素。光纖線路特性中對CNR有直接影響者為元件對光 信號的反射,反射衰減量的大小對電路CNR有相當之關係。因仳,CATV線路測試過程中,是以 改善CNR為重頭戲。現行光纖品質及接續技術精進,連接器的接續損失越來越低,電路末端功 率的維持已不是問題了。為了滿足調幅有線電視的傳輸特性,各種光纖被動式通信元件的反射 衰減量大幅提高。有線電視線路在可預見的未來,仍是利用既有的電信光纜。為了快速提供 業者電路,如何將電信線路改善以符合視訊傳輸?是線路人員需面對的挑戰! |
英文摘要 | Owing to its low attenuation, EMI imunity, and durability, fiber-optic link is regarded as the best choice for the trunk of CATV distribution network. Lots of CATV carriers in Taiwan rent fiber links from Chunghwa Telecom to replace the coaxial trunks of their plant. To provide a good and efficient service to these customers presents quite a challenge to the technicians of the company. Although AM optical fiber link is not the state of the art, it is new when a telecommunication fiber-optic link, that has always been used to transmit digital signal which is much more robust than analog signal, is used to transmit TV signals of hundred channels, especially for the personnel who design and construct the link. This is always the case at the initial converging stage of CATV and telecommunication industries. Carrier to noise ratio (CNR) is a critical parameter reflecting the picture quality of a CATV system, and is strongly dependent upon the quality of fiber-optic link installation under the circumstance that both the optical transmitter and receiver are properly specified. As the splice technology gets advanced, splice loss becomes less and less. Optical power at the end of the link is always not a significant factor deteriorating the CNR. It is that the optical return loss (ORL) from passive devices in fiber link, such as splitter, connector, and attenuator, plays an important role in system CNR detriment. The higher the return loss is, the better the CNR will be; however, there is a point at which increasing the return loss will have no effect. It can be said that the CATV outside plant won't be complete without a good CNR parameter. Each passive device reflects different amount of light. This paper tells how these devices affect the system's CNR. |
本系統之摘要資訊系依該期刊論文摘要之資訊為主。