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The carrier frequency is 500kHz, the input is 20kHz, and the output is 520kHz. If the input was 10kHz, the output would be 510kHz. If the input had a 10kHz frequency component and a 20kHz frequency component, then the output would have a 510kHz frequency component and a 520kHz frequency component. The is achieved by mixing (multiplying) the carrier and input in a Gilbert cell mixer, and doing the same thing in another Gilbert cell mixer, but with the inputs 90 degree phase shifted by a Hilbert transform such that every harmonic in the two inputs of the Gilbert cell is phase shifted independently. The two mixed signals are then combined with two resistors leaving nothing but the upper sideband which is at 520kHz in this case. If you want the lower sideband, then invert the signal coming from one of the Gilbert cell mixers. If you want to change the input, make sure to change the input of both Gilbert cell mixers and phase shift the right one by 90 degrees, and if there are multiple harmonics then make sure to phase shift all harmonics by 90 degrees independently.
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