调频接收机外文资料.docx

1、调频接收机外文资料the major technical indicators FM receiver1.Receiver operat ing freque ncy range can receive the radio wave freque ncy rangeis called the receiver operati ng freque ncy range or band coverage. Freque ncyreceiver and tran smitter freque ncy must corresp ond. Such as FM radio broadcast freque

2、 ncy range of 88 108MH, FM radio because the scope of work for 88 108MHz2.Receiver sensitivity as the ability to receive weak signal sensitivity, usuallythe size of the in put sig nal voltage, said in put sig nal received smaller, highersen sitivity. FM radio sen sitivity is usually 5 30uV.3.Selecti

3、ve receiver from a variety of signals and interferenee signals requiredto select (or atte nu ati on of unwan ted sig nals) capacity as selective un its with dB(decibels) that the higher the dB number, the better selectivity. FM radiofreque ncy in terfere nee should be greater tha n 50dB.4.Freque ncy

4、 range of the freque ncy resp onse of the receiver freque ncycharacteristics or the pass band is called. FM Machine passband typically 200KHz.5.Receiver output power maximum load output without distorti on (or non li neardistorti on factor for a give n value) power as the output power.FM receiver wi

5、th FM receiver worksFigure 1 Block diagram of FM receiverOrdinary FM receiver block diagram shown in Figure 1. Its working principleis: high-freque ncy antenna receives the sig nal, selected by the in put freque ncytuning circuit for the f1, and then amplified by high-frequency amplification stagein

6、to the mixer stage. The local oscillator output frequency f2 is also another level into the mixer, the mixer output level with f1, f2, (f1 + f2), (f2-f1) and other frequency components of signals. Mixer stage circuit output then select FM IF signal (f2-f1), then amplified by IF, was sufficiently hig

7、h gain, then Kam-frequencylow-frequency modulated signal is demodulated, amplified by the low frequency amplifier stage. Due to the high frequency antenna signal through the mixing of a fixed frequency, plus to zoom, so the higher the receiver sensitivity, good selectivity, the performance is relati

8、vely stable.1.High-frequency power amplifier circuit as shown is connected incommon-emitter transistor-level high-frequency small-signal amplifier.He not only high-frequency signal amplification, but also the role of certain selected frequency, so the load transistor LC parallel resonant circuit. In

9、 the high-frequency case, the transistor itself and the wiring capacitances of the distribution parameters will affect the frequency and phase. Quiescent operating point of transistors by the resistance RA2, RA3, RA4 and RA6 decision, it is calculated with the same low-frequency single-tube amplifie

10、r.ANTA1 received from the antenna frequency signal through the CA1, CCA1,LA1 constitution of the frequency loop, select the signal fs = 10.7MHZ the useful signal, amplified by transistors QA1to by CA3, TA1 primary component of the tuning circuit, further filtering In addition to unwanted signals, th

11、e useful signal by the transformer and the CB1 coupling into the MC3361.KAI2.Mixer circuit for frequency and low frequency than the external signalis fixed, in termediate freque ncy amplifier gain easy access to relativelylarge, thereby enhancing the sensitivity of the radio. But fixed at a lowerfre

12、que ncy, but also can be more complex loop systems or filter freque ncy select ion. They have close to the ideal recta ngular selectivity curve, the higher adjace nt cha nnel selectivity. Achieved only if the device freque ncy, oscillati on sig nal gen erated by other devices is called the mixer.Dio

13、de ring balaneed mixer circuit of four diodes as shown below.Constitute the diode ring mixer circuit, the diodes are working in the reference sig nal con trolled by the state of the switch, it is ano ther switching multiplier.Has the following characteristics:A structure of four diodes connected to

14、form a ring. As a mixer, the ring of two angles of side AB and CDaccess to the local oscillator signal through the tran sformer and the useful sig nal VL VS.2If the circuit bala nee, the n the port is isolated, that is, L-port ofthe local oscillator signal will not pass to the R side, R port of the

15、desired signal will not be fleeing into L side, useful signal and local oscillator signal will not pass to the I end.3Gain, there is loss. As a mixer, the mixing theory of value loss 4dB4for the amplitude modulation, taking into account the frequency characteristics of high-frequency transformers ha

16、ve poor low frequency modulation signal change from the port input, the carrier signal from the port input, the output amplitude modulation signal from the terminal.3.IF amplifier IF amplifier circuits task is to get the IF frequency signal to be amplified, then sent to detector detector. Superheter

17、odyne radio frequency amplifier circuit on the sensitivity, selectivity and passband performance indicators such as playing an important role. The figure (a) is a single-tuned LC IF amplifier, Figure (b) equivalent circuit for its exchange. Figure B1, B2 for the intermediate frequency transformers,

18、respectively and C1, C2 component input and output frequency selection network, but also played the role of impedance transformation, therefore, intermediate frequency transformers is a key component in the discharge circuit.IF transformer primary coil and the capacitance to form a parallel resonant

19、 LC circuit, due to the parallel resonant circuit on the natural frequencyof the signal impedance Yi large non-resonant frequency of the signal impedance small. So IF signal IF transformers primary coil to generate significant pressure drop, and coupled to the next level of magnification, the pressu

20、re drop of non-resonant frequency of the signal is very small, almost short circuit (usually it only through the intermediate frequency signal), thereby complete the selected frequency, and improve the selectivity of the receiver.Known by the LC resonance circuit characteristics, IF frequency select

21、ion circuit passband B = f2-f1 = fd / QL, QL is the type of load circuit quality factor. QL value is higher, the better selectivity, the more narrow passband; the contrary, the more wide-passband selectivity worse.(a)电路 (b交流等效电路4.Discrim in ator circuit diagram is un der the freque ncy discrim in at

22、orcircuit schematic. It is composed of three loops FMtuner - AMFMconverter and Ion gitud inal symmetry composed of two amplitude detector. Primarycircuit resonant frequency at the center of the FMsignal, a wide passband.调频接收机的主要技术指标1.工作频率范围接收机可以接受到的无线电波的频率范围称为接收机的工作频率范围或波段覆盖。接收机的工作频率必须与发射机的工作频率相对应。如

23、调频广播收音机的频率范围为88108MH，是因为调频广播收音机的工作范围也为 88108MHz2.灵敏度接收机接收微弱信号的能力称为灵敏度，通常用输入信号电压的大小来表示，接收的输入信号越小，灵敏度越高。调频广播收音机的灵敏度一般为 530uV。3选择性接收机从各种信号和干扰中选出所需信号（或衰减不需要的信号）的能力称为选择性，单位用dB （分贝）表示dB数越高，选择性越好。调频收音机的中频干扰应大于 50dB。4频率特性接收机的频率响应范围称为频率特性或通频带。调频机的通频带一般为 200KHz。5.输出功率接收机的负载输出的最大不失真（或非线性失真系数为给定值时）功率称为输出功率。调频接收

24、机组成调频接收机的工作原理图一调频接收机组成框图一般调频接收机的组成框图如图一所示。其工作原理是：天线接受到的高频信号，经输入调谐回路选频为fl，再经高频放大级放大进入混频级。本机振荡器输出的另一高频 f2亦进入混频级，则混频级的输出为含有 fl、f2、（ f1+f2 ）、（ f2-f1 ）等频率分量的信号。混频级的输出接调频回路选出中频信号（ f2-f1 ）,再经中频放大器放大，获得足够高增益,然后鉴频器解调出低频调制信号， 由低频功放级放大。由于天线接收到的高频信号经过混频成为固定的中频，再加以放大，因此接收机的灵敏度较高，选择性较好，性能也比较稳定。1. 高频功率放大电路如下图所示为共射

25、级接法的晶体管高频小信号放大器。 他不仅要放大高频信号， 而且还要有一定的选频作用，因此晶体管的负载为 LC并联谐振回路。在高频情况下，晶体管本身的极间电容及连接导线的分布参数等会影响的频率和相位。晶体管的静态工作点由电阻 RA2,RA3,RA4及RA6决定，其计算方法与低频单管放大器相同。从天线ANTA1接收到的高频信号经过 CA1 CCA1 LA1组成的选频回路，选取信号为 fs=10.7MHZ的有用信号，经晶体管 QA1进行放大，由CA3 TA1初级组成的调谐回路，进一 步滤除无用信号，将有用信号经变压器和 CB1耦合进入MC33612.混频电路因为中频比外来信号频率低且固定不变， 中频

26、放大器容易获得比较大的增益， 从而提高收音机的灵敏度。在较低而又固定的中频上， 还可以用较复杂的回路系统或滤波器进行选频。 它 们具有接近理想矩形的选择性曲线， 因此有较高的邻道选择性。 如果器件仅实现变频， 振荡 信号由其它器件产生则称之为混频器。二极管环形混频器 四个二极管组成平衡电路如下图所示。 构成的二极管环形混频电路中， 各二极管均工作在受 参考信号控制的开关的状态，它是另一类开关工作的乘法器。具有如下特点：1结构上四个二极管接成环形。作为混频时，环形的两个对角端 AB和CD通过变压器接入本 振信号VL和有用信号VS.2如果电路平衡，则各端口是相互隔离的，即L端口的本振信号不会通到

27、R端,R端口的有用 信号不会窜入 L 端, 有用信号和本振信号均不会通到 I 端.3有增益 ， 存在损耗 . 作为混频器时 ， 混频损耗的理论值为 4dB4为调幅器时 ， 考虑到高频变压器的低频频率特性差的缺点 ， 调制信号改从端口输入 ， 载波信 号从端口输入 ， 从端输出振幅调制信号 .3.中频放大电路中频放大电路的任务是把变频得到的中频信号加以放大， 然后送到检波器检波。 中频放大电路对超外差收音机的灵敏度、选择性和通频带等性能指标起着极其重要的作用。下图（a）是LC单调谐中频放大电路，图（b）为它的交流等效电路。图中 B1、B2为中频变压器，它们分别与 C1、C2组成输入和输出选频网络

28、，同时还起阻抗变换的作用，因此， 中频变压器是中放电路的关键元件。中频变压器的初级线圈与电容组成 LC并联谐振回路，由于并联谐振回路对诣振频率的信号阻抗很大， 对非谐振频率的信号阻抗较小。 所以中频信号在中频变压器的初级线圈上产 生很大的压降， 并且耦合到下一级放大， 对非谐振频率信号压降很小， 几乎被短路 （通常说 它只能通过中频信号），从而完成选频作用，提高了接收机的选择性。由LC调谐回路特性知，中频选频回路的通频带 B= f2- fl = fd/QL，式中QL是回路的有载品质因数。QL值愈高，选择性愈好，通频带愈窄；反之 ，通频带愈宽，选择性愈差。(a)电路 (b交流等效电路4.鉴频电路下图是回路鉴频器的原理图。它是由三个调谐回路组成的调频 -调幅调频变换电路和上下对称的两个振幅检波器组成。初级回路谐振于调频信号的中心频率 ，其通带较宽。