Indeed. This is why the LSC PDs have a 2f notch in addition to the 1f resonance. In recent versions, we also put a 2f notch in the feedback of the preamp which comes after the diode but before the mixer. The overall 1f to 2f ratio that we get is in the 50-60 dB region. I don't think we have to go that far with this thing; having a double LC already seems like it should be pretty good, or we could have a single LC bandpass with a 2f notch all in one Pomona box.