What's the Superheterodyne receiver?

To better understand the superheterodyne reception, we can first understand the ordinary direct amplifier receiver. The working process of the direct-amplification receiver is to receive the signal from the antenna, directly amplify the received high-frequency or low-frequency signal, and do not carry out frequency conversion before the detection, so the sensitivity to the high and low bands will be different. Uniform tuning is also very difficult, and the gain of the high-frequency amplifier is not high, and self-excitation is easy to occur.

Superheterodyne receiver is to convert the high-frequency signal received by the receiver into an intermediate frequency signal through a mixer and then output the intermediate frequency signal to the detection circuit. This intermediate frequency signal is a fixed difference signal obtained by subtracting the local oscillator frequency and the received signal frequency​. The basic superheterodyne receiver is a single IF conversion receiver, and a variant of the superheterodyne receiver is a dual IF conversion receiver, which has two IFs both converted into fixed IF signals for amplification and detection. Since the IF frequency is lower than the signal frequency before conversion, and the frequency is fixed, the signal of any radio station can get equal amplification, and the total amplification can also be higher, thus overcoming the direct-amp reception. problem. Since the IF frequency is lower than the signal frequency before conversion, and the frequency is fixed, the signal of any radio station can get equal amplification, and the total amplification can also be higher, thus the direct-amp receiver of the problem is overcome.