專業(yè)英語(yǔ)考試復(fù)習(xí)總結(jié)-免費(fèi)閱讀
【正文】 An analog information source produces messages that are defined on a continuum, whilea digital information source produces a finite set of possible messages. (2)我國(guó)古代的烽火臺(tái)也是一個(gè)通信系統(tǒng) The beaconfire tower in ancient China was a munications system. (3)證明當(dāng)發(fā)出二進(jìn)制數(shù)1和0的概率相等時(shí)，熵（entropy）是最大的 Show that the entropy is a maximum when the probability of sending a binary 1 is equal to the probability of sending a binary 0 . (4) 信息容量是在給定時(shí)間內(nèi)，通信系統(tǒng)能傳送多少信息的量度Information capacity is a measure of how much information can be transferred through a munications system in a given period of time . (5) 帶寬越寬，傳送時(shí)間越長(zhǎng)，系統(tǒng)傳送的信息越多The wider the bandwidth and the longer the time of transmission, the more information can be conveyed through the system .3． Translate the following sentences into English. (lesson12)(1)波分復(fù)用發(fā)射器更加復(fù)雜，因?yàn)樗芏喙ぷ饔诓煌ㄩL(zhǎng)光源的，每一個(gè)光源都有它自己的電子部分。然而它通常提供更高的性能。亞力山大格雷厄姆貝爾發(fā)明電話早了四年，但他認(rèn)為光影電話是他最偉大的發(fā)明。其中一個(gè)輸入是具有單一高頻的等幅載波信號(hào)；另一個(gè)輸入是頻率相對(duì)較低的信息信號(hào)，它可能是單頻的，也可能是有很多頻率組成的復(fù)雜波形。② 波形成形器。但因電流最大，故電感周圍的磁場(chǎng)能量達(dá)到最大。?所需的頻率穩(wěn)定性?頻率是可變的嗎？如果是，其變化范圍是什么？ ④允許的波形失真。當(dāng)在射頻或更高頻率選用線圈和電容器時(shí)，還有另一個(gè)特性是必須考慮的，這就是元件的品質(zhì)因數(shù)（Q）。Electrical noise may be defined as any undesired voltages or currents that ultimately end up appearing in the receiver output. To the listener this electrical noise often manifests itself as static. It may only be annoying, such as an occasional burst of static, or continuous and of such amplitude that the desired information is obliterated. 電氣噪聲可以定義為最終出現(xiàn)在接收機(jī)輸出端的任何不希望的電壓或電流。Basically, there are two forms of data pression:?Lossless pression operates by removing the redundant information contained in the data of interest. The pression is said to be lossless because it is pletely reversible in that the original data can be reconstructed exactly. Lossless pression is also referred to as data paction.?Lossy pression involves the loss of information in a controlled manner。The signal can be onedimensional, as in the case of speech, music, or puter data。Electronic munication can be summarized as the transmission , reception , and processing of information between two or more locations using electronic circuits .電子通信就是利用電路在兩地或多地之間進(jìn)行信息的發(fā)送、接收和處理。 twodimensional, as in the case of pictures。 the pression may therefore not be pletely reversible. Lossy pression is, however, capable of achieving a pression ratio radio higher than that attainable with lossless methods.基本上，有兩種形式：數(shù)據(jù)壓縮的無(wú)損壓縮通過(guò)去除冗余信息包含在感興趣的數(shù)據(jù)。對(duì)聽(tīng)者來(lái)說(shuō)，電氣噪聲常表現(xiàn)為靜電噪聲。Q是元件儲(chǔ)能與耗能的比值。⑤所需的輸出功率。該磁場(chǎng)能量因失去電容器電壓的維持而開(kāi)始減小，但其反電動(dòng)勢(shì)將保持電流按相同的方向流動(dòng)。③ 幅度調(diào)制器(選用)。The location in a transmitter where modulation occurs determines whether the circuit is a low
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