Its common for radio amateurs to underestimate the importance of a good antenna. Many GMDX members advocate spending more effort (and money!) on the antenna system than on tranceivers for best results. Here's some interesting sites with antenna advice.
Antennas by W4RLN. The late prof Leroy Bruce Cebik was a theoretical expert in antenna design.
AC6V's home brew antenna page
W8JI antenna pages
ARRL antenna page