The Goertzel algorithm effectively calculates a single line of the FFT by multplying the input signal with a discrete complex sinewave of the respective frequency and summing the product over the indended sequence length. So it requires to know the fundamental frequency. If your intended output is a continuous fundamental wave, I would prefer a band pass filter. Of course an analog filter can be used as well. If you don't need the signal in the digital domain, I would be the preferred method anyway, and with limited processor resources, possibly also as an analog pre-filter.