I'm looking to build an antenna to research the 5-500 Hz range. I already had decent success with just a simple square loop 1.5 ft per side (air core), about 12 turns. Despite having an estimated resonant freq. approx. 4 MHz, inside the house, it does easily pick up all the odd harmonics of the power line frequency. But weaker signals are extremely faint and below 60 Hz the spectrogram is all noise.
I will be using a ferrite rod for an improved loop antenna (mu-metal is too expensive for me). I found an excellent tutorial here on building an induction coil antenna (http://www.vlf.it/romero3/ics101.html) that rivals far more expensive commercial antennas. I will be constructing a "poorer-man's version" of his design.
Can anyone recommend (or, even better, supply a schematic for) a simple but reasonably effective pre-amp for my "poorer-man's version"? The Romero design has a 3-stage pre-amp + 1-stage supply and I'm looking for something simpler, even if performance is less. My main concern is decent dynamic range in the 5-200 Hz segment (areas above this seem easier), keeping in mind the power line harmonics can be quite high.