專業(yè)英語考試復(fù)習(xí)總結(jié)-展示頁(yè)
2025-04-25 12:51本頁(yè)面
【正文】 heel effect .圖44（a）中的電容器先充電到某個(gè)點(diǎn)位，然后閉合開關(guān)就會(huì)產(chǎn)生圖44（b）所示的波形。⑤所需的輸出功率。振蕩器類型的選擇基于如下的考慮：?所需的輸出頻率。波形可以是任何形狀，但總有某一重復(fù)頻率。振蕩器是能把直流能量轉(zhuǎn)換成交流的一種電路。Q是元件儲(chǔ)能與耗能的比值。類似地，電容器有一個(gè)標(biāo)稱電容量，以法拉（F）為單位；還有一個(gè)額定的最大電壓。在研究通信系統(tǒng)時(shí)，考慮噪聲的重要性，再怎么強(qiáng)調(diào)都不過分。 The noise present in a received radio signal has been introduced in the transmitting medium and is termed external noise. The noise introduced by the receiver is termed internal noise. The important implications of noise considerations in the study of munications systems cannot be overemphasized .接受信號(hào)中由傳輸媒介引入的噪聲稱為外部噪聲。對(duì)聽者來說，電氣噪聲常表現(xiàn)為靜電噪聲。希望的部分稱為信號(hào)，而不希望的部分成為噪聲。有損壓縮，然而，能夠?qū)崿F(xiàn)壓縮比無線電高于無損方法實(shí)現(xiàn)。無損壓縮也被稱為數(shù)據(jù)壓縮。 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)壓縮的無損壓縮通過去除冗余信息包含在感興趣的數(shù)據(jù)。因此，如果在一個(gè)字節(jié)一個(gè)單點(diǎn)接收誤差，從而違反奇偶校驗(yàn)規(guī)則，它可以檢測(cè)并更正通過重傳。Suppose, for example, the munications agree to use even parity 。 and fourdimensional, as in the case of volume data over time.信息可以是一維的，例如語音、音樂和計(jì)算機(jī)數(shù)據(jù)；也可以是二維的，例如圖像；也可以是三維的，例如視頻數(shù)據(jù)；還可以是四維的，例如隨時(shí)間變化的立體空間數(shù)據(jù)The type of scanning used in television is a form of a spatial sampling called raster scanning, which converts a twodimensional image intensity into onedimensional waveform。 twodimensional, as in the case of pictures。Information capacity is a measure of how much information can be transferred through a munications system in a given period of time信息容量是在給定時(shí)間內(nèi),能通過通信系統(tǒng)傳送多少信息的量度。例如,話音頻率包含300Hz到3000Hz的信號(hào)。The bandwidth of a munications channel must be large (wide) enough to pass all significant information frequencies. In other word, the bandwidth of the munications channel must be equal to or greater than the bandwidth of information. For example, voice frequencies contain signals between 300Hz and 3000Hz. Therefore, a voicefrequency channel must have a bandwidth equal to or greater than 2700Hz.信道的帶寬必須足夠大(寬),以便所有重要的信息頻率都能通過。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。Regardless of the particular application, all munications systems involve three main subsystems: the transmitter, the channel, and the receiver.無論何種具體應(yīng)用，通信系統(tǒng)都包括三個(gè)主要的子系統(tǒng)：發(fā)送機(jī)、信道和接收機(jī)。換句話說,信道的帶寬必須等于或大于信息的帶寬。因此,話音頻率的信道必須具有等于或大于2700Hz的帶寬。The signal can be onedimensional, as in the case of speech, music, or puter data。 three dimensional, as in the case of video data。 it is somewhat analogous to the manner in which we read a printed paper in that the scanning is preformed
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