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1、调幅无线电历史Main articles: History of radio anOldest radio station 无线电的历史及早期的无线电电台AM was the dominant method of broadcasting during the first eighty years of the 20th century and remains widely used into the 21st.可以追溯到可以可以追溯到20世纪前八十年 ，利用调幅无线电通信进行广播是非常有效的方式，进入二十一世纪，这一方式，仍被广泛采用。 AM radio began with the fir
2、st, experimental broadcast on Christmas Eve of 1906 by Canadian experimenter Reginald Fessenden , and was used for small-scale voice and music broadcasts up until World War I . San Francisco, California radio station KCBS claims to be the direct descendant of KQW, founded by radio experimenter Charl
3、es Doc Herrold, who made regular weekly broadcasts in San Jose, California as early as June of 1909.调幅广播开始的第一次，是在圣诞前夕的1906年由加拿大研究者Reginald Fessenden 实验播出，并直至第一次世界大战，用它进行了小规模的语音和音乐播放。旧金山，加利福尼亚州电台KCBS自称是KQW的继承者，由无线电实验者Charles Doc Herrold，在加利福尼亚州圣何塞建立的，每周定期播出的广播成立于1909年6月。在此基础上KCBS自称是世界上最古老的广播站 ，并在2009
4、年夏天庆祝成立100周年。第一次世界大战后，随着无线电试验站在世界范围的广泛增多，调幅无线电的应用得到了广泛地增加，第一次的调幅无线电商业 广播 服务始于20世纪20年代。 Montreal XWA，Quebec （后来的CFCF，现在的CINW）宣称作为世界第一大商业电视台的地位，于1920年5月20日开始正式广播。 The first licensed American radio station was started by Frank Conrad , KDKA in Pittsburgh , Pennsylvania . Radio programming boomed during
5、 the Golden Age of Radio (1920s1950s). Dramas, comedy and all other forms of entertainment were produced, as well as broadcasts of news and mu首家拥有正常营业执照的美国电台由Frank Conrad, KDKA 在Pittsburgh, Pennsylvania开始营业，无线电节目的大发展还是在“ 无线电黄金时代 ”（20世纪20-50年代）。这一时期戏剧，喜剧和所有其他形式的娱乐都相继得到创造发展，而广播新闻和音乐也不例外。 edit Operatio
6、n AM radio technology is simpler than FM radio , DAB , Satellite Radio and HD Radio 调幅收音机的技术要比调频收音机、DAB、卫星广播和高清广播简单得多。An AM receiver detects amplitude variations in the radio waves at a particular frequency. It then amplifies changes in the signal voltage to drive a loudspeaker or earphones 一个调幅接收器在
7、一个特定频率检测无线电波的振幅变化。然后通过放大信号电压来驱动扬声器或耳机。最早的 晶体收音机接收器 使用没有放大功能的 晶体二极管探测器。In North American broadcasting practice, transmitter power input to the antenna for commercial AM stations ranges from about 250 watts to 50,000 watt 在北美的广播实践，商业调幅电台传到天线的发射功率从约250瓦-5万瓦特。实验许可证上表明最多发出五十万瓦特辐射功率，在灾害时期，包括广域通信的通信站，包括Cin
8、cinnati的通信站 WLW，这种辐射功率一直到第二次世界大战前都在用。WLW的超大功率发射机仍然保留在郊区发射现场，但它是在40年代初期退役，并且在当时的美国美国或加拿大的商业电视台都没有这样功率级的授权。其他一些国家也授权高功率运行（例如， 墨西哥 XERF 曾是一个拥有二十五万瓦特的发射站）。天线的设计必须考虑所需的覆盖面 ， 必须直接发射信号 ， 以免干扰其他电视台在同一或相邻的频率运行。Medium-wave and short-wave radio signals act differently during daytime and nighttime.中波和短波无线电信号在白天
9、和夜间的传输是不同的。During the day, AM signals travel by groundwave , diffracting around the curve of the earth over a distance up to a few hundred miles (or kilometers) from the signal transmitter.白天，调幅信号依靠地面波传输，围绕地球的发射曲线距离可达几百英里（或公里）。然而，在夕阳，由于电离层 的变化调幅信号通过空中波传送，这使调幅广播电台在太阳落山后将白天时发射的远得多。This phenomenon can
10、be easily observed by scanning an AM radio dial at night. As a result, many broadcast stations are required as a condition of license to reduce their broadcasting power significantly (or use directional antennas) after sunset, or even to suspend broadcasting entirely during nighttime hours.这种现象可以很容易
11、地通过扫描夜间的调幅收音机拨号来观察到。因此，许多广播电台要求许可条件规定，可以减少它们在夜间的发射功率，有的甚至提议（或使用落后，甚至定向天线）完全停止夜间广播。这些电视台通常被称为daytimers。In the United States and Canada, some AM radio stations are granted clear channel status, meaning that they broadcast on frequencies with few other stations allocated, allowing an extended coverage
12、area.在美国和加拿大，有些调幅广播电台被授予清晰通道的地位，这意味着它们与分配的广播电台频率的其他几个，允许扩大覆盖范围。 Relatively few stations enjoy clear-channel status. 相对而言 ， 很少站享受到清晰通道的地位。商业广播公司通常依靠地面波作为其仅有的广告目标市场。The hobby of listening to long distance signals is known as DX or DXing, from an oldtelegraph嗜好聆听长途信号被称为DX 或DXing，由旧的电报缩写为“距离”。有几个非营利hobb
13、yist clubs are devoted exclusively to DXing the AM broadcast band , including the National Radio Club and International Radio Club of America.业余爱好者 俱乐部专门为远程接收的AM广播频段 ，包括国家广播俱乐部和美国的国际无线电俱乐部。同样，人们听短波传输的称为 SWLing。 Frequency bands频带 AM radio is broadcast on several frequency bands.调幅广播的节目于多个频带。这些频段的分配是由
14、国际电联 管拧 无线电管理条例 ，并在国家一级，每个国家的电信管理（即 联邦通讯委员会 在 美国 ，例如）受国际协定。 Long wave is 148.5 kHz 283.5 kHz, with 9 kHz channel spacing generally used.长波 是148.5 千赫 -283.5千赫频率间隔为9普遍使用的渠道。长波用于无线电广播的欧洲，非洲和亚洲部分地区（ 国际电联地区 1），而不是在西半球分配。在美国和加拿大，百慕大和美国领土这个频段主要用于航空预留导航设备虽然是乐队的一小部分在理论上可用于在美国部分 microbroadcasting 15 规则。由于长波信号
15、的传播特性，使用的频率是最有效地在纬度50度以北。 Medium wave is 520 kHz1,610 kHz.中波 520千赫 -1，610千赫。 In the Americas (ITU region 2) 10 kHz spacing is used; elsewhere it is 9 kHz.在美洲（国际电联地区2）10千赫间隔使用，在其他地方是9千赫。ITU region 2 also authorizes the Extended AM broadcast band between 1610 kHz and 1710 kHz.国际电联地区2还授权 至1610千赫和1710千赫
16、 扩展AM广播频段。Medium wave is by far the most heavily used band for commercial broadcasting.中波是目前商业广播最频繁使用的频段。这是“调幅广播”，大多数人都熟悉。Short wave is 1.711 MHz30.0 MHz, divided into 15 broadcast bands.短波是1.711兆赫-30.0兆赫，为15个广播频段的划分。短波广播通常使用5 kHz的一条狭窄通道间距。短波目的所使用的音频服务能够从很远的距离发射台听到。的短波广播，远程是在上个音频保真度较低的费用。用于短波传播模式是不同
17、的（见 高频 ）。上午主要是用来通过广播服务-其他短波用户可使用修改后的版本，如调幅 单边带 或上午兼容版本的评审委员会评审等与运营商重新插入。Frequencies between the broadcast bands are used for other forms of radio communication, and are not broadcast services intended for reception by the general public.广播频段之间的频率用于无线通信的其他形式，而不是对于公众的广播服务。 edit Limitations局限性Because o
18、f its susceptibility to atmospheric and electrical interference, AM broadcasting now attracts mainly talk radio and news programming, while music radio and public radio mostly shifted to FM broadcasting in the late 1970s.因为它容易受大气和电气干扰，调幅广播现在吸引主要谈话类节目和 新闻节目，而音乐电台和公共广播大多转向70年代末的调频广播。然而，在1960年代末和70年代，前
19、40岩石，如WABC和覃德在美国和加拿大推出台发射的高度加工和延长至11 kHz的音频，成功地吸引了大量观众。在英国，20世纪80年代 ，BBC广播4台（一大部分讲话频道）有一个调频的位置，而英国广播公司电台第一 ，音乐频道，只限于在英国多为AM广播。频率响应通常是40赫兹- 5150 分贝 千赫S/N比。The limitation on AM fidelity comes from current receiver design.调幅的保真度的限制来自目前的接收机设计。此外，为了适应更多在调幅广播频段的发射机，美国最大的传输音频带宽的限制在了由FCC通过的对1989年6月 1 NRSC有关
20、标准的10.2千赫 ，导致20.4 kHz的带宽被占用。先The former audio limitation was 15 kHz resulting in a channel occupied bandwidth of 30 kHz.前对于音频限制为15千赫导致30 kHz的带宽被占领。AM radio signals can be severely disrupted in large urban centres by metal structures, tall buildings and sources of radio frequency interference (RFI) a
21、nd electrical noise, such as electrical motors, fluorescent lights, or lightning调幅的无线电信号可能会受到金属结构、高大建筑物、射频源（RFI）和电气噪声的严重干扰， 如电动机，荧光灯，或闪电在大型城市中心。因此，调幅收音机在许多国家已经失去了作为音乐广播服务的主导地位，并在许多城市正在沦为新闻，体育，宗教和谈话电台站。Some musical genres particularly country, oldies, nostalgia and ethnic/world music survive on AM, e
22、specially in areas where FM frequencies are in short supply or in thinly populated or mountainous areas where FM coverage is poor.有些人-特别是国家，老歌，怀旧，民族/世界音乐-音乐流派上午生存，特别是在超短波频率短缺或在人烟稀少的地区或山区调频，普及率仍然很低。 其他应用方式Stereo transmissions are possible (see AM stereo ), and hybrid digital broadcast systems are now
23、 being used around the world.立体声 传输（见 AM立体声 ），和混合数字广播系统是可能并正被广泛采用于世界各地。在美国，iBiquity公司 的专有 高清收音机 已被采纳和联邦通讯委员会批准的中波转播，而数字无线电广播通用 经常在 短波波段 使用是将一个更加开放的努力 ，并且将与众多调幅广播并行使用。这些标准都比当下的调幅带宽限制以及0-16千赫频率响应的理论有着更高质量的保真度，除了立体声声音和文字数据。While FM radio can also be received by cable , AM radio generally cannot, althou
24、gh an AM station can be converted into an FM cable signal虽然调频收音机也可以通过 有线电视 接收 ，调幅收音机一般不能，虽然是调幅站能够通过有线调频信号转换。 In Canada , cable operators that offer FM cable services are required by the CRTC to distribute all locally available AM stations in this manner.在 加拿大 ，有线运营商提供CRTC调频有线电视服务到当地现有的所有调幅方式站。在瑞士，一个
25、“有线广播”之称的系统通过电话线上的长波波段来发送调幅信号。 edit Microbroadcasting微型发射机 微型发射机Some microbroadcasters and pirate radio broadcasters, especially those in the United States under the FCCs Part 15 rules, broadcast on AM to achieve greater range than is possible on the FM band .一些微型发射机和 海盗电台广播，特别是美国的根据FCC的 第15章 规定，对AM
26、广播实现更大范围比在 调频波段 的可能。在中波（调幅），这些电台经常能在1610千赫和1710千赫间被探测到。Hobbyists also use low-power AM transmitters to provide local programming for antique radio equipment in areas where AM programming is not widely available or is of questionable quality; in such cases the transmitter, which is designed to cover
27、only the immediate property and perhaps nearby areas, is hooked up to a computer or music player.业余爱好者也可以使用一些老式收音机设备通过低功率调幅发射在调幅节目不是广泛使用的或质量有问题的地方采用，在这种情况下，发射器，用来覆盖靠近的建筑物和可能的邻近地区，连接着电脑或音乐播放器。 edit References8AM broadcastingHistoryAM was the dominant method of broadcasting during the first eighty yea
28、rs of the 20th century and remains widely used into the 21st.AM radio began with the first, experimental broadcast on Christmas Eve of 1906 by Canadian experimenter Reginald Fessenden, and was used for small-scale voice and music broadcasts up until World War I. San Francisco, California radio stati
29、on KCBS claims to be the direct descendant of KQW, founded by radio experimenter Charles Doc Herrold, who made regular weekly broadcasts in San Jose, California as early as June of 1909. On that basis KCBS has claimed to be the worlds oldest broadcast station and celebrated its 100th anniversary in
30、the summer of 2009. The great increase in the use of AM radio came late in the following decade as radio experimentation increased worldwide following World War I. The first licensed commercial radio services began on AM in the 1920s. XWA of Montreal, Quebec (later CFCF, now CINW) claims status as t
31、he first commercial broadcaster in the world, with regular broadcasts commencing on May 20, 1920. The first licensed American radio station was started by Frank Conrad, KDKA in Pittsburgh, Pennsylvania. Radio programming boomed during the Golden Age of Radio (1920s1950s). Dramas, comedy and all othe
32、r forms of entertainment were produced, as well as broadcasts of news and music.Operation AM radio technology is simpler than FM radio, DAB, Satellite Radio and HD Radio. An AM receiver detects amplitude variations in the radio waves at a particular frequency. It then amplifies changes in the signal
33、 voltage to drive a loudspeaker or earphones. The earliest crystal radio receivers used a crystal diode detector with no amplification.In North American broadcasting practice, transmitter power input to the antenna for commercial AM stations ranges from about 250 watts to 50,000 watts. Experimental
34、licenses were issued for up to 500,000 watts radiated power, for stations intended for wide-area communication during disasters including Cincinnati station WLW, which used such power on occasion before World War II. WLWs superpower transmitter still exists at the stations suburban transmitter site,
35、 but it was decommissioned in the early 1940s and no current commercial broadcaster in the US or Canada is authorized for such power levels. Some other countries do authorize higher power operation (for example the Mexican station XERF formerly operated at 250,000 watts). Antenna design must conside
36、r the coverage desired and must direct the transmitted signal so as not to interfere with other stations operating on the same or adjacent frequencies.Medium-wave and short-wave radio signals act differently during daytime and nighttime. During the day, AM signals travel by groundwave, diffracting a
37、round the curve of the earth over a distance up to a few hundred miles (or kilometers) from the signal transmitter. However, after sunset, changes in the ionosphere cause AM signals to travel by skywave, enabling AM radio stations to be heard much farther from their point of origin than is normal du
38、ring the day. This phenomenon can be easily observed by scanning an AM radio dial at night. As a result, many broadcast stations are required as a condition of license to reduce their broadcasting power significantly (or use directional antennas) after sunset, or even to suspend broadcasting entirel
39、y during nighttime hours. Such stations are commonly referred to as daytimers.In the United States and Canada, some AM radio stations are granted clear channel status, meaning that they broadcast on frequencies with few other stations allocated, allowing an extended coverage area. Relatively few sta
40、tions enjoy clear-channel status. Commercial broadcasters generally rely on the ground-wave coverage only as their target market for advertising.The hobby of listening to long distance signals is known as DX or DXing, from an old telegraph abbreviation for distance. Several non-profit hobbyist clubs
41、 are devoted exclusively to DXing the AM broadcast band, including the National Radio Club and International Radio Club of America. Similarly, people listening to short wave transmissions are SWLing.Frequency bandsAM radio is broadcast on several frequency bands. The allocation of these bands is gov
42、erned by the ITUs Radio Regulations and, on the national level, by each countrys telecommunications administration (the FCC in the U.S., for example) subject to international agreements.Long wave is 148.5 kHz283.5 kHz, with 9 kHz channel spacing generally used. Long wave is used for radio broadcasti
43、ng in Europe, Africa and parts of Asia (ITU region 1), and is not allocated in the Western Hemisphere. In the United States and Canada, Bermuda and U.S. territories this band is mainly reserved for aeronautics navigational aids, though a small section of the band could theoretically be used for micr
44、obroadcasting under the United States Part 15 rules. Due to the propagation characteristics of long wave signals, the frequencies are used most effectively in latitudes north of 50. Medium wave is 520 kHz1,610 kHz. In the Americas (ITU region 2) 10 kHz spacing is used; elsewhere it is 9 kHz. ITU reg
45、ion 2 also authorizes the Extended AM broadcast band between 1610 kHz and 1710 kHz. Medium wave is by far the most heavily used band for commercial broadcasting. This is the AM radio that most people are familiar with. Short wave is 1.711 MHz30.0 MHz, divided into 15 broadcast bands. Shortwave broad
46、casts generally use a narrow 5 kHz channel spacing. Short wave is used by audio services intended to be heard at great distances from the transmitting station. The long range of short wave broadcasts comes at the expense of lower audio fidelity. The mode of propagation for short wave is different (s
47、ee high frequency). AM is used mostly by broadcast services other shortwave users may use a modified version of AM such as SSB or an AM-compatible version of SSB such as SSB with carrier reinserted. Frequencies between the broadcast bands are used for other forms of radio communication, and are not
48、broadcast services intended for reception by the general public.Limitations Because of its susceptibility to atmospheric and electrical interference, AM broadcasting now attracts mainly talk radio and news programming, while music radio and public radio mostly shifted to FM broadcasting in the late
49、1970s. However, in the late 1960s and 1970s, top 40 rock and roll stations in the US and Canada such as WABC and CHUM transmitted highly processed and extended audio to 11 kHz, successfully attracting huge audiences. In the UK during the 1980s, BBC Radio 4 (a largely speech channel) had an FM location, whereas BBC Radio 1, a music channel, was confined to AM broadcasts over much of the UK. Frequency response is typically 40 Hz5 kHz with a 50 dB S/N ratio. The limitation on AM fidelit