You could use a few taps of binary selected caps and then a smaller number
of the higher ratio variable caps.
Every stage of dinary selection allows a halving of varicaps needed.

Or a mechanically variable unit :-).
Piezo, memory wire, linear actuator, motor driving fine thread, stepper,
 ... .  :-)
--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.