THE RDF PROJECT. Radio Direction Finding of VLF and LF transmissions:
http://www-user.uni-bremen.de/~ews2/RDF_project.htm

Klaus’ Radio Page:
http://longwave.bei.t-online.de/
Where you also find a very useful RDF calculator:
http://longwave.bei.t-online.de/rdf.html

The world below 535kHz, by Costas Krallis SV1XV
http://www.qsl.net/sv1xv/index.html

Tony Field’s azimuth map v3.2:
http://members.shaw.ca/ve6yp/
mirror at: http://www.qsl.net/ve6yp/

Sheldon C. Shallon’s (W6EL) propagation and azimuth map program, W6ELProp v2.02. The map section is very useful for building up a library of VLF bearings:
http://www.qsl.net/w6elprop/

Mother Nature’s own cacophony of signals and noise in the VLF range. Stephen P. McGreevy, VLF sounds and samples:
http://www-pw.physics.uiowa.edu/mcgreevy/

NASA’s online VLF receiver:
http://spaceweather.com/glossary/inspire.html
http://science.nasa.gov/headlines/y2001/ast19jan_1.htm

Larry’s VLF site, sounds, schematics and much more:
http://home.pon.net/785/

WUN, World Utility News:
www.wunclub.com

The use of Frequency Selective Voltmeters as VLF receivers, by Don Moman:
http://members.home.net/rnewll/fsvm.htm

For construction of ground dipoles:
http://www.elfrad.com
http://www.elfrad.org
http://www.da4e.nl/elfspecial.html

For construction of induction coil antennas and ELF receivers:
http://wavelab.homestead.com/

For various ELF /ULF research, including spectrograms of the 2.5 Hz signal:
http://members.home.net/sidereal7/elfulf_research_in_arizona.htm

Loop antennas for VLF and below:
http://home.t-online.de/home/Peter.Schmalkoke/

Maps and coordinates, worldwide:
http://www.calle.com/world
http://new2calle.com/world