Hi, my high school astronomy class designs/builds antennas to detect VLF radio for solar flare detection. Recently, and regardless of their design, we get a strange "mirrored" shape to the dB vs frequency plot. The shape of the graph before roughly mid-band is exactly mirrored about the center. The antennas are all small loop designs. We use an amplifier circuit provided from Stanford, and feed the signal into a soundcard (96kHz sampling rate). The computer is running linux and Stanford software (a python based program that does db vs frequency, and db vs time for selected frequency) and is usually rock solid. I don't remember changing anything about our monitoring station before this started happening. Hoping some antenna gurus can provide some insight. Here is a rough sketch of whats happening...luckily this does not seem to be affecting the db vs time plot which is used to interpret flare occurrence. Something that also adds to the curiosity is that the frequency we are monitoring occurs on the axis of reflection.