I was looking for some information on how to compute the resonant frequencies that are attainable from small loop antennas, especially for VLF. This appears to be precisely what I’m looking for.
This article describes how to build a loop antenna for low frequency (LF) and medium wave (MW) reception with remote-controlled tuning. The antenna is extremely sensitive and can be built mostly from parts from old radios and tape recorders. Like all loop antennas, it is highly directional, which allows you to null out unwanted noise sources.