What is the maximum frequency range of a Clapp or Vackar oscillators?

At the end of Russell McMahon's answer to this question (High-stability oscillators (non-crystal)) there is this reference:

"Shows that Gouriet-Clapp, Seiler, and Vackar oscillators have equivalent frequency stability given equal resonator Q. They differ only in how much the amplitude of oscillation changes when they are tuned. The three circuits are useful over frequency ranges of 1.2, 1.8, and 2.5 to one, respectively." (J. K. Clapp, "Frequency Stable LC Oscillators," Proc. IRE, Aug 1954.)

Does this mean that if I design a Gouriet-Clapp oscillator to have a frequency of 100MHz, I can change the tuning capacitor to give me a frequency range of 100 to 120MHz?

Background: I want to take advantage of the dielectric properties of soil and use it as a tuning capacitor in a variable frequency oscillator running at >80MHz (I need frequencies >80MHz in order to minimise the effect of minerals in the soil). The only catch is that the dielectric constant of the soil will vary between 4 and 80 depending upon how wet the soil is, which means that the value of the soil capacitor will vary from 10pF (calculated) to 400pF.

• Way, way over the top - if your capacitance changes that much you don't really need a high stability oscillator; you just need an oscillator like a conventional colpitts. Commented Sep 26, 2017 at 10:21
• There are probably more issues in the way how your sensor works then int he oscillator electronics. I would build the oscillator and try it with one of the old 500pF trimmer caps and with you sensor and see how it behaves with both. Commented Sep 26, 2017 at 14:08
• @Andyaka How do you make sure that such a large change in capacitance doesn't upset the feedback to the LC tank circuit (because it will change either C1 or C2)? Could I place the soil sensor in parallel with either one of the tank circuit capacitors? Commented Sep 26, 2017 at 21:30
• Or could I place the sensor in parallel with both C1 and C2? Commented Sep 26, 2017 at 22:47