無線電廣播外文翻譯

1、<p>　　Modern civil and military facilities using electronic equipment is various, electromagnetic environment complex, mutual interference serious. Generally, cars, boats and planes of the communication equipment to

2、 send and receive machines were integrated together. To shortwave communication equipment, for example, the remnants of the signal transmitter in receiver input from the level of 120 dB µ V (i.e. 13 dBm) or higher.

3、And for the weak signal receiver receive level may only-6 ~ 0 dB µ V (namely</p><p>　　Radio stations in order to make the voice signal out, the launch of the electromagnetic wave must with audio signal.

4、 Audio signal is through a modulator of various signal sound to be treated. It's very low frequency, such as the frequency of the voices in about 300 Hz ~ 3000 Hz, music frequency general in frequency 50 Hz ~ 15000 H

5、z, the frequency is to pass out, must be put in the low frequency signal with high frequency electromagnetic wave, such a process called modulation, not the modulation </p><p>　　The sending system and the re

6、ceiving system two parts of Radio system mainly b. Radio is the basic process of signal transmission, the transmission, receiving process. After the sender, will need to spread information, such as voice, text, images, a

7、nd low frequency signal, into electrical signal, through the modulator "modulation" in the high frequency carrier, and then by the transmitter through the antenna radiation to the air to, and with radio in the

8、form of electromagnetic wave propagation </p><p>　　At present, the ground of radio and television points do VHF (less or says m wave) and UHF (especially high frequency or say Fen Mi Bo) two frequency band.

9、In our country, the frequency of use TV VHF frequency range is 48.5 MHz ~ 300 MHz, divided into 1 ~ 12 channels, UHF band use frequency range is 470 MHz to 956 MHz, divided into: 3 ~ 68 channels. They basically are to re

10、ly on space wave propagation. The provisions of the international satellite radio and television have six frequency band, th</p><p>　　現(xiàn)代民用及軍用設施使用電子設備繁多，電磁環(huán)境復雜，相互干擾嚴重。一般地，車、船和飛機上的通信設備收發(fā)機都集成在一起。以短波通信設備為例，發(fā)射機的殘

11、余信號在接收機輸入端產(chǎn)生的電平達120dBµV（即13dBm）或更高。而接收機所需接收的微弱信號電平可能僅-6～0dBµV（即-117～-113dBm）。因此，要求接收機處理的信號動態(tài)范圍高達120～126dB。另外，高電平干擾信號與所接收信號頻率僅相距數(shù)十千赫，所以，高電平干擾信號和它們在接收機中產(chǎn)生的互調(diào)產(chǎn)物會嚴重影響接收機的輸出信噪比。為了降低這種影響，就要求接收機具有以下性質(zhì)：高選擇性，接收機的動態(tài)范圍盡可能

12、要大；高線性，在信道濾波之前，降低帶外高電平干擾信號在信道濾波器通帶內(nèi)產(chǎn)生的互調(diào)產(chǎn)物；?極低的本振相位噪聲，以免鄰近的干擾信號將本振噪聲轉(zhuǎn)換到接收機信道帶寬內(nèi)。作為接收機重要組成部分的接收機射頻前端是接收機動態(tài)性能的關(guān)鍵部件，它工作于中頻放大器之前。諸如動態(tài)范圍、互調(diào)失真、-1dB壓縮點和三階互調(diào)截獲點等，都與接收機前端的性能有直接關(guān)系。</p><p>　　無線電廣播是利用無線電波向廣大接收者播送聲音節(jié)目的通信

13、過程，屬于無線電通信范疇。廣播電臺為了把聲音信號傳遞出去，發(fā)射的電磁波必須帶有音頻信號。音頻信號是通過一個調(diào)制器把各種聲音信號加以處理而來的。它的頻率很低，如人聲的頻率大約在300Hz～3000HZ,音樂頻率大體在50Hz～15000HZ，這樣的頻率是傳送不出去的，必須再把低頻信號加在高頻電磁波里，這樣的過程叫做調(diào)制，未調(diào)制的高頻電磁波叫載波。音頻信號必須與載波結(jié)合起來，才能把聲音信號傳送到遠方。人們收聽廣播電臺的廣播節(jié)目時，就是接收到

14、載有低頻信號的電磁波</p><p>　　無線電廣播系統(tǒng)主要由發(fā)送系統(tǒng)和接收系統(tǒng)兩部分組成。無線電廣播的基本過程是信號的發(fā)送、傳輸、接收的過程。在發(fā)送端，將需要傳播的信息，如聲音、文字，圖像等低頻信號，轉(zhuǎn)換成電信號后,經(jīng)調(diào)制器“調(diào)制”在高頻載波上，然后由發(fā)射機通過發(fā)射天線輻射到空中去，并以無線電電磁波的形式進行遠距離傳播。在接收端，這些已調(diào)制的高頻無線電波被接收機天線接收下來，經(jīng)過解調(diào)和一系列處理后，回復成原來的

15、低頻信息。接收機是一種從天線接收并解調(diào)無線電信號的電子設備，主要用于聲音，圖像定位信息等。 “收音機''和“無線電接收機”一般特別指只接收和播放聲音的接收機，盡管其他的象電視機技術(shù)也是無線電接收設備。目前，地面的廣播電視分做VHF(甚高頻或稱米波)和UHF(特高頻或稱分米波)兩個頻段。在我國，VHF頻段電視使用的頻率范圍是48.5MHz～300MHz，劃分成1～12頻道，UHF頻段使用的頻率范圍是470MHz～956MH