首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
There are three basic sections which make up a receiver: the tuner or radio signal receiving section, the preamplifier control s
There are three basic sections which make up a receiver: the tuner or radio signal receiving section, the preamplifier control s
admin
2010-06-18
30
问题
There are three basic sections which make up a receiver: the tuner or radio signal receiving section, the preamplifier control section, and the power amplifier section. In very elaborate hi fi systems these three sections actually may be purchased as separate units, for increased flexibility and control or as a means of assembling the system in stages using the "building block" approach.
The Tuner Section
The tuner section may be equipped to receive only FM signals or both AM and FM signals. Since it is possible to broadcast stereo (two channel) sound via FM, most hi fi receivers have circuitry for decoding the complex composite received signal into separate "left and right" channel signals.
The front end of the tuner section selects the particular signal desired from the hundreds of radio signals present in the atmosphere. As you tune the dial, resonant or tuned circuits are changed so as to be responsive to a single frequency. In the case of FM signals, tuning is adjustable from 88 MHz (millions of alternations/second of the radio wave) to 108 MHz. Since each FM station occupies a space of 0.2 MHz, that means a theoretical maximum of 100 stations is possible in one geographical area. Actually fewer stations are assigned in any one area, so that one station’ s signal will not cause audible interference with an adjacent station. In the case of AM, stations broadcast at frequencies ranging from 540 kHz to 1605 kHz (1 kHz = 1000 alternations per second) and selection of desired stations is similar to the technique used in FM.
The signal is amplified by the front end and mixed with a locally generated signal in the receiver to produce a different frequency known as the IF signal (Intermediate Frequency). In the case of AM, the IF frequency is generally 455 kHz. In the case of FM radio, the IF frequency is 10.7 MHz. The process is known as super heterodyne and since the local signal and received signal are always a fixed amount apart, the succeeding IF amplifiers need not be variably tuned but can be designed simply to amplify 455 kHz (for AM) or 10.7 MHz (for FM).
Difference Between FM and AM
In AM radio the amplitude of the radio wave is varied in accordance with the audio information to be broadcast. Hence the name Amplitude Modulation. In FM it is the radio frequency that is varied based on audio signals. It is this feature that makes FM relatively noise free since noise or static is an amplitude phenomenon. If noise accompanies the FM signals the noise can be sliced off by circuits called limiters without impairing the frequency-changing nature of the FM signal.
While the circuits themselves differ, the amplified IF signals are then applied to a detector circuit which strips off the original audio information. In FM, the detector is called a radio detector. The output of either the AM detector or the FM detector is an audio signal suitable for application to and further processing by the "preamplifier control" section o{ the receiver.
In the case o{ stereo FM the recovered audio signal must be further processed or "unscrambled" to recover the separate "left" and "right" audio channels. This is accomplished by the multiplex decoder circuits.
In an FM radio, the Intermediate Frequency is usually ______.
选项
A、10.7 MHz
B、455 kHz
C、540 kHz
D、1605 kHz
答案
A
解析
转载请注明原文地址:https://kaotiyun.com/show/ihlO777K
0
专业英语八级
相关试题推荐
Fromitsbirth,threepowerfulimageshavecolouredideasofwhattheUnitedStateswasandwhatitstoodfor.Onewas"acityo
Thecars,SUVsandpickupspeoplewillbuyintheyearsaheadarelikelytouselessfuel,andmanywillrelyonethanolorhous
Goodmorning.Thediscussiontopicfortoday’sseminaris"HomelessnessinAmerica."IntheUnitedStates,homelessnesshas【C1】
Goodmorning.Thediscussiontopicfortoday’sseminaris"HomelessnessinAmerica."IntheUnitedStates,homelessnesshas【C1】
Oursisanagrarianeconomy.Wemustbecomeself-sufficientinfoodtofeedarapidlygrowingpopulationatanannualgrowthrat
SocialpsychologydevelopedintheUSAAccordingtotheauthor,socialpsychologyshouldhelpmanto
Thethreatofaglobaloutbreakofbirdflumakesiturgentfortheinternationalcommunitytocooperateeffectively.Wealthyco
NowtheU.S.economygrowthrateis______.
TheRenaissancebeganin______intheearly14thcentury.
Toseehowbigcarrierscouldcontroltheonlineworld,youmustunderstanditsstructures.EarthlinkgivesJenniferaccesst
随机试题
根据《行政处罚法》规定,违法行为在二年内未被发现的,不再给予行政处罚。法律另有规定的除外()
6有机化工产品的特性与它的()有密切关系。
腊肠犬,雌性,8岁,不愿挪步,行动困难,不愿让主人抱。精神欠佳,食欲下降,腹围增大,尿失禁,肛门反射迟钝,触诊腰部皮肤紧张、痛叫。根治该病最有效的方法是
职业道德评价的作用有()。
建筑屋面各汇水范围内,雨水排水立管不宜少于()根。
公司希望通过历史数据和资料来预测下一年的市场销量,比较适合采用()。
公安机关在办理刑事案件中,在()应当用当地通用的语言进行讯问。
(单选题)近年来,网咖呈高速发展之态势,让人欢喜让人忧。喜的是网咖出现是我国经济快速发展的产物,是开放社会的一个象征;忧的是一些网咖无序发展,唯利是图,衍生社会公害。网咖发展的“让人欢喜让人忧”表明()。
若α∥β,α={6,3,一2},而|β|=14,求β.
A、Theylosttheirway.B、Theyforgotwhattheyweredoing.C、Theyweresleepy.D、Theyhadmentalmistakes.B该题问“根据本段,为什么人们在疲倦时易于
最新回复
(
0
)