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New for November 2019. Microwave engineers use tons of different analogies to offer simple explanations for concepts that may be hard to visualize, often resorting to plumbing, sound waves or even ocean waves. We offer a new analogy to see how a mixer works, using a pair of mismatched pocket combs. You might have thought this page was going to dive into comb generators. That's going to be a future topic, someday.
Comb #1 has roughly 20 teeth per inch. Let's call it the RF signal.
RF signal
Comb #2 has fewer teeth, maybe 16 per inch. Let's call it the local oscillator (LO)
Local oscillator
Here is what happens when you shove then together. You can still see the two "signals" but you can observe a lower frequency signal. at ~4 cycles per inch. This occurs at the same frequency when you subtract the RF and LO signals.
RF, LO and IF "signals"
It is kind of sorrowful that we had to cut the ears of that blue comb to make this work. On the other hand, some of us are hair challenged and don't really need a comb anyway...