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1、the major technical indicators FM receiver1. Receiver operating frequency range can receive the radio wave frequency range is called the receiver operating frequency range or band coverage. Frequency receiver and transmitter frequency must correspond. Such as FM radio broadcast frequency range of 88
2、 108MH, FM radio because the scope of work for 88 108MHz2. Receiver sensitivity as the ability to receive weak signal sensitivity, usually the size of the input signal voltage, said input signal received smaller, higher sensitivity. FM radio sensitivity is usually 5 30uV.3. Selective receiver from a
3、 variety of signals and interference signals required to select (or attenuation of unwanted signals) capacity as selective units with dB (decibels) that the higher the dB number, the better selectivity. FM radio frequency interference should be greater than 50dB.4. Frequency range of the frequency r
4、esponse of the receiver frequency characteristics or the pass band is called. FM Machine passband typically 200KHz.5. Receiver output power maximum load output without distortion (or nonlinear distortion factor for a given value) power as the output power.FM receiver with FM receiver worksFigure 1 B
5、lock diagram of FM receiverOrdinary FM receiver block diagram shown in Figure 1. Its working principle is: high-frequency antenna receives the signal, selected by the input frequency tuning circuit for the f1, and then amplified by high-frequency amplification stage into the mixer stage. The local o
6、scillator 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 high gain, then Kam-frequency low-
7、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 relatively stable.1. High-frequency
8、power amplifier circuit as shown is connected in common-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 the high-frequency case, t
9、he 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 amplifier.ANTA1 received from the a
10、ntenna frequency signal through the CA1, CCA1, LA1 constitution of the frequency loop, select the signal fs = 10.7MHZ the useful signal, amplified by transistors QA1 to by CA3, TA1 primary component of the tuning circuit, further filtering In addition to unwanted signals, the useful signal by the tr
11、ansformer and the CB1 coupling into the MC3361.2. Mixer circuit for frequency and low frequency than the external signal is fixed, intermediate frequency amplifier gain easy access to relatively large, thereby enhancing the sensitivity of the radio. But fixed at a lower frequency, but also can be mo
12、re complex loop systems or filter frequency selection. They have close to the ideal rectangular selectivity curve, the higher adjacent channel selectivity. Achieved only if the device frequency, oscillation signal generated by other devices is called the mixer.Diode ring balanced mixer circuit of fo
13、ur diodes as shown below. Constitute the diode ring mixer circuit, the diodes are working in the reference signal controlled by the state of the switch, it is another switching multiplier.Has the following characteristics:A structure of four diodes connected to form a ring. As a mixer, the ring of t
14、wo angles of side AB and CD access to the local oscillator signal through the transformer and the useful signal VL VS.2 If the circuit balance, then the port is isolated, that is, L-port of the local oscillator signal will not pass to the R side, R port of the desired signal will not be fleeing into
15、 L side, useful signal and local oscillator signal will not pass to the I end.3 Gain, there is loss. As a mixer, the mixing theory of value loss 4dB4 for the amplitude modulation, taking into account the frequency characteristics of high-frequency transformers have poor low frequency modulation sign
16、al change fromthe port input, the carriersignal 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. Superheterodyne 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 ampl
