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【正文】 se. Quiescent operating point of transistors by the resistance RA2, RA3, RA4 and RA6 decision, it is calculated with the same lowfrequency singletube amplifier. ANTA1 received from the antenna frequency signal through the CA1, CCA1, LA1 constitution of the frequency loop, select the signal fs = the useful signal, amplified by transistors QA1 to by CA3, TA1 primary ponent of the tuning circuit, further filtering In addition to unwanted signals, the useful signal by the transformer 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 more plex 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 four 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 two 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, Lport of the local oscillator signal will not pass to the R side, R port of the desired signal will not be fleeing into L side, useful signal and local oscil
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