Designing a VHF Colpitts oscillator using BJT
The transistor is used as a transconductor: voltage input, with current output. In which case, the GM (transconductance) computed at Ie / 0.026volts, give the value. At 1mA, GM is 1/39; at 10m1, GM is 1/3.9; at 26mA, GM is 1/1 (1 amp per volt).

Your bipolar's task is to work with AC input voltage on the emitter, and output a collector current into the tank.

Its also your task to fully recognize the entire circulating path of the RF energy; some Colpitts use the VDD as part of the circulating path, and forget about the bypass capacitor; this is not good; huge losses.







simulate this circuit &ndash; Schematic created using CircuitLab

What POWER are you asking this oscillator to provide?

Power = F * C * Vrms^2 = 500e6 * 10pF (minimum) * 15*0.707 * 15*0.707

Power = 0.5e+9 * 1e-11 * 225 * (0.707*0.707) = 0.5e-2 * 225 = 1.13/2 watts.

Power = 0.56 watts.