varactors are also used in PLL circuits to voltage control the oscillator.
i don't exactly know what you are asking about "resolving frequency control"..... do you mean to use one varactor for coarse frequency control, and a smaller one for fine tuning?
i've used 2N2222 transistors connected across the Local Oscillator cap in an old FM tuner to frequency modulate the LO, then use the LO as the basis for a low power FM station. one old Delco car radio i did this with didn't even need the 2N2222 installed, the AFC (automatic frequency control) varactors did the trick nicely when audio was inserted (and the rest of the AFC loop disconnected)