A previous poster suggested what I'd called a "synthetic reactance", which
is a series-parallel LC combination. This technique can produce very large
effective-capacitance changes with a modest varactor range, however it
also
comes with the susceptibility of mode-jumping in the output frequency.

Joe
W3JDR
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But perhaps the most important effect of this method of creating a
multi-band or wideband tuned circuit is big deterioration in effective
operating Q.


Once upon a time it was a popular PA tuned-tank, minimum-dip, arrangement.
At the higher frequencies the coils got hot. Too high a circulating current
in the tank. Poor efficiency. They didn't catch on!


Varactor diodes used in receiver and local oscillator circuits have a
relatively poor Q to begin with. Perhaps lower than coil Q. Series tuned
circuits in parallel with shunt tuned circuits only magnify adverse varactor
effects.
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Reg, G4FGQ