【導(dǎo)讀】線電通信進(jìn)行廣播是非常有效的方式，進(jìn)入二十一世紀(jì)，這一方式，仍被廣泛采用。舊金山，加利福尼亞州電臺KCBS自稱是KQW的繼承者，由無線電實驗者Charles. 在此基礎(chǔ)上KCBS自稱是世界上最古老的廣播站，并在2021年夏天慶祝成。第一次世界大戰(zhàn)后，隨著無線電試驗站在世界范圍的廣泛增多，調(diào)幅。大商業(yè)電視臺的地位，于1920年5月20日開始正式廣播。首家擁有正常營業(yè)執(zhí)照。的美國電臺由FrankConrad,KDKA在Pittsburgh,Pennsylvania開始營業(yè)，無線。劇，喜劇和所有其他形式的娛樂都相繼得到創(chuàng)造發(fā)展，而廣播新聞和音樂也不例外。接收器在一個特定頻率檢測無線電波的振幅變化。許可證上表明最多發(fā)出五十萬瓦特輻射功率，在災(zāi)害時期，包括廣域通信的通信站，時的美國美國或加拿大的商業(yè)電視臺都沒有這樣功率級的授權(quán)。調(diào)幅信號依靠地面波傳輸，圍繞地球的發(fā)射曲線距離可達(dá)幾百英里（或公里）。陽落山后將白天時發(fā)射的遠(yuǎn)得多。因此，許多廣播電臺要求許可條件規(guī)定，可以減少它們在夜間的。調(diào)幅的保真度的限制來自目前的接收機(jī)設(shè)計。

　　

【正文】 ers on the AM broadcast band, in the United States maximum transmitted audio bandwidth is limited to kHz by an NRSC standard adopted by the FCC in June of 1989, resulting in a channel occupied bandwidth of kHz. The former audio limitation was 15 kHz resulting in a channel occupied bandwidth of 30 radio signals can be severely disrupted in large urban centres by metal structures, tall buildings and sources of radio frequency interference (RFI) and electrical noise, such as electrical motors, fluorescent lights, or lightning. As a result, AM radio in many countries has lost its dominance as a music broadcasting service, and in many cities is now relegated to news, sports, religious and talk radio stations. Some musical genres – particularly country, oldies, nostalgia and ethnic/world music – survive on AM, especially in areas where FM frequencies are in short supply or in thinly populated or mountainous areas where FM coverage is poor. Other distribution methods Stereo transmissions are possible (see AM stereo), and hybrid digital broadcast systems are now being used around the world. In the United States, iBiquity39。s proprietary HD Radio has been adopted and approved by the FCC for medium wave transmissions, while Digital Radio Mondiale is a more open effort often used on the shortwave bands, and can be used alongside many AM broadcasts. Both of these standards are capable of broadcasting audio of significantly greater fidelity than that of standard AM with c urrent bandwidth limitations, and a theoretical frequency response of 016 kHz, in addition to stereo sound and text FM radio can also be received by cable, AM radio generally cannot, although an AM station can be converted into an FM cable signal. In Canada, cable operators that offer FM cable services are required by the CRTC to distribute all locally available AM stations in this manner. In Switzerland a system known as wire broadcasting transmits AM signals over telephone lines in the longwave band. Microbroadcasting 5 Some microbroadcasters and pirate radio broadcasters, especially those in the United States under the FCC39。s Part 15 rules, broadcast on AM to achieve greater range than is possible on the FM band. On mediumwave (AM), such radio stations are often found between 1610 kHz and 1710 kHz. Hobbyists also use lowpower 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 only the immediate property and perhaps nearby areas, is hooked up to a puter or music player. 出處： google 網(wǎng)調(diào)幅無線電搜索結(jié)果第一條 （英文）