Bill, I remember in your Soldersmoke book that you had difficulty for a long time trying to understand how a mixer created the sum and difference frequencies, and how this was accomplished in a diode ring mixer. I know that you've got it all sorted out now, but I thought this was a good topic for a video anyway.
Here's my video on the subject:
Alan: Thanks. Great stuff. Yea, I've been looking at the innards of mixers for a long time. In my book, I try to explain how I have come to understand the physics of the mixing action -- how the use of a non-linear element causes two signals to "multiply" and how this "multiplication" results in sum and difference frequencies. I tried to go beyond the trig functions because for me the trig didn't really explain anything.
In the book I was looking at the classic two diode mixer (beloved of Doug DeMaw!). A few years later, on the blog, I was looking at the action of the diode ring. I concluded that there is a big difference between how the diode ring works and how the two diode mixer works. RSGB provided a great diagram:
I guess one way of describing the difference between a two diode mixer and a diode ring would be to say that the more simple mixer multiplies the signal by 0 and 1 (if it is operating in "switching mode), while the diode ring multiplies by 1 and -1.
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