Difference Frequencies: A frequency mixer has inputs of 1.45 MHz and 1 MHz. What is the difference frequency? How is a spurious signal defined?

Answer: The difference frequency is 0.45 MHz, equivalent to 450 kHz. The harmonics of the input signals also produce difference frequencies. A spurious signal is defined as any higher-order difference frequency that is less or equal to the desired difference frequency, in this case, 450 kHz. The difference frequency f23 is shown in yellow to indicate that it is a spurious signal. Frequency f23 is produced by the second harmonic of 1.45 MHz and the third harmonic of 1 MHz.

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