What combination of a mixer's Local Oscillator (LO) and RF input frequencies is found in the output?
Why A mixer is a nonlinear device that multiplies two signals together, and the trigonometric identity for multiplying two sine waves produces components at the sum and the difference of the two input frequencies. So feeding in an RF signal and a local oscillator gives outputs at LO + RF and LO - RF, and a filter then selects whichever one you want as the IF. This is the basis of superheterodyne receivers and transmitters: a 14.2 MHz signal mixed with a 5.0 MHz LO yields 19.2 MHz and 9.2 MHz.
Watch out The arithmetic product is tempting because the mixer literally multiplies the two waveforms in the time domain, but multiplying in time does not create a signal at the product of the frequencies; in the frequency domain it creates the sum and difference.
Mixers multiply in time but add and subtract in frequency: out comes LO+RF and LO-RF.