Super heterodyne demodulation circuit is to set up a local oscillating circuit to generate oscillating signals. After mixing with the received carrier signal, get the frequency(usually 465kHz) signal, through medium frequency amplification and detection wave, detach the data signal.
Since the carrier frequency is fixed, the sensitivity of the super heterodyne can reach 100-104dbm, few peripheral components, high integration, suitable for mass production. There are two types of frequency stabilization for super heterodyne, SAW and LC. LC stabilization capability is not so good, it is less used now. Saw stabilization is good, its stabilization sensitivity is about -100dbm.
The impedance matching requirement of super heterodyne receiver for antenna is high, The required impedance of the external antenna must be 50ohm, Otherwise, it has a great effect on the sensitivity of the receiver. The length of lead from the base of the antenna to the soldering point of the transmitting module antenna should be reduced as much as possible. If it can not be reduced, it can be connected by a radio frequency coaxial cable with characteristic impedance 50ohm.
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