Of course, you CAN build the capacitor, but unless you want to do it for
fun and/or education, why re-invent the wheel? Dan's Small Parts and
Kits sells several nice capacitors.

http://www.danssmallpartsandkits.net/

The capacitors aren't necessarily "dirt cheap", but a manufactured
capacitor will be physically stable, insuring smooth change in
capacitance as the shaft is rotated.

Scott
N0EDV

Jim wrote:
i need a variable for a receiving loop antenna. does anyone know how to
determine the area of plates for a given value of cap? for example i
need 365 pf. two half circle plates would be handy, separated by a piece
of plastic or card stock. what surface area for each plate would
approximate that value? does two stator plates with one rotor between
them increase the value if compared to one plate each?