I was busy last week....but since promised some ideas
here is a primer on main part of vlf/ulf receiver....
For the end i sugest a simple 10.7 IF from some radio
.....for example u can use some based on CA3089 or even
better on MC3357 or similar...3361,3371,3362,3359.....
even a simple transistor design would do a job.Further
analyze can be obtained,taking a part of signal from
later stage....(i am preparing some schematic on that).
For antena I would sugest a loopstick or even better
special design i am preparing and gonna post it soon.
You may experiment by winding 600-100 wind. of Cul 0.5mmm
on ferrite core, 30-45cm long and 3-6cm thick.
This is just an idea,I am very busy these days and off
.net so here is a little something just for a start.
regards....