This page hosts a repository of downloadable documents (or links) of use the DXer or Contester.
HF Contesting Tips by GM3WOJ.pdf
Intro to HF Radio.pdf A superb document from IPS in Australia covering HF propagation
VOAcap by N6BV.pdf VOACap and take off angles by N6BV
OffsetMultibandTraplessAntenna.pdf An Offset Multiband Antenna
bploop.pdf A Bandpass Loop Ant for VLF
BPloops2.pdf Part 2 of bandpass Ant for VLF
http://www.g0ksc.co.uk/ G0KSC's site where high performance antennas are described as well as sold. This site is a valuable technical resource, not just a sales site, though of course purchases can be made too.
Manuals (for rigs, amps etc)
OPER_MAN A1000.pdf Acom 1000 Linear Amp Manual