knarz,
The coils are "loading coils." For a complete explanation, as well as some of the real detailed formulas, get the ARRL book on antenna design. I believe that is probably where B. Oblivion got his figures. I haven't read that antenna page in some time, but I recall some info there or on the original l0pht site which lead me to believe that he is ham.

Same thing on the decoupling tube. The tube is used to match impedance in the coax cable to the antenna. For the details, look in the ARRL antenna book or some other books on antenna design.

Cheers,
Thorn