超外差接收机是一种利用超外差原理的无线电接受机，1918年由美国无线电工程师埃德温·霍华德·阿姆斯特朗发明。超外差原理是一种利用机器内一个可变的振荡器产生的电波和外来信号混合以产生固定频率的中频信号（通常调幅无线电是450千赫兹或455千赫兹（也有262.5千赫兹），调频无线电是10.7 兆赫兹）。

设 f 为外来信号的频率

为可变的内部振荡器产生的信号的频率。

经过混频后得到 =455 千赫兹/10.7兆赫兹。

In electronics, a superheterodyne receiver (often shortened to superhet) uses frequency mixing to convert a received signal to a fixed intermediate frequency (IF) which can be more conveniently processed than the original carrier frequency. It was invented by US engineer Edwin Armstrong in 1918 during World War I. Virtually all modern radio receivers use the superheterodyne principle. At the cost of an extra frequency converter stage, the superheterodyne receiver provides superior selectivity and sensitivity compared with simpler designs.