L1C1 are selected to be resonant at a frequency below the desired crystal harmonic but above the crystal`s next lower odd harmonic. C2 should have a value of 30-70 pF, independent of the oscillation frequency. There is no requirement for any specific ratio of C1/C2, but practical harmonic circuits seem to work best when Cl is approximately 1-3 times the value of C2. Diodes D1-D3 provide a simple regulated bias supply
The resistance of Rl should be as high as possible, as it affects the crystal"s in-circuit Q.