What kind of sound are you looking for at the output? A beep or a crackle or?
OK; is this better?
(The bandpass filter would need to be adjustable to track the selected oscillator frequency.)
This on the other hand:
will not work at all.
All you will get is the sum of the incoming voltages, the frequencies will not change.
If the input frequencies are F1 and F2, the output frequencies will also be F1 and F2.
A radio mixer as distinct from an audio mixer is a multiplicative thing where the frequencies add and subtract.
You misunderstand what I am trying to say.OK, whoa. Why would RF be different from AF in this respect?