Amazing Antenna.  I plan to build one.  Looking for suppliers for the russian variety of ferrite, used, including the one of special shape that avoids the "sticks of dynamite" visual look, that gives pause to shippers... Where can I get some of the usable varieties of ferrite? 
There was mention made of the effectiveness of the variable capacitor chosen for this antenna.   I am very interested in knowing any variable capacitor characteristics that assist in maximum signal.    Most  300-400 pF capacitors look very similar.  What sets your selection apart from "garden variety" capacitors in that capacitance range that works especially well in this application?