10.58 to 10.74 MHz VFO Oscillator CircuitFigure 1 shows the 10.58 to 10.74 MHz VFO oscillator circuit. Yes, this is the same circuit that was presented last, but I've re-designed to show the Colpitts oscillator more clearly. "L" is approximately 1.5 uh, 19 becomes a core T50-6 (yellow). The value of C6 is found experimentally. I 69 pF (47 pF to 22 pF and a parallel). More information about this during check-out.
"L" and the VVC with C6 form the parallel-tuned circuit that determines the frequency of the VFO. The CVV is a MV2104. Capacitors marked with an asterisk are required Silvered Mica, COG or NPO.
You might wonder how the component values for the resonance circuit is determined. Well, when Jupiter aligns with Mars and Mercury on the cusp of the new moon, if the inductive reactance equals the capacitive reactance, then we have a resonance circuit. For a given frequency there are infinite combinations of L and C is a resonance circuit. Experience shows that the variable capacitors and VVC in the range of 5 to 300 pF pF are quite practical. Combine this with the fact that UH 1.5 coil and a capacitor of 150 pF resonate near the frequency of interest, and has the component values for the resonance circuit this VFO. You can find the formulas to calculate all this in your manual if you like to do arithmetic. The values of the components actually used in the circuit to take into account "stray" inductance and capacitance that occurs in the real world. More information about this during check-out.
Resonant circuits are fascinating creatures! Although I did not go into a theoretical discussion, there are some fundamental characteristics of resonant circuits that you (and me) should be considered in the construction of VFO, filters, amplifiers, etc.
There are two types of resonant circuits commonly used are the series resonant circuit and parallel resonant circuits, as shown below. Here are two important things to consider: Parallel resonant circuits reduce the flow of AC current in the resonant frequency (and pass all other frequencies) pass resonant series circuit of alternating current in the resonant frequency (and mitigate all the other frequencies).
