practical colpitts ocilator

sparky 1

Joined Nov 3, 2018
783
variable colpitts.png

Practical and inexpensive, has many uses.
This Colpitts variable frequency generator outputs 2-10 MHz sine wave.
A simple low or high pass filter will bring out the harmonics.
Adding a simple wide band amplifier stage makes it even more practical.
 
Last edited:

MisterBill2

Joined Jan 23, 2018
19,389
One caution is that if an FET or MOSFET is used for the active device, you really MUST have that source to common resistor, and a higher value is better. The reason is that with excessive gain there will be clipping and lots of harmonics in the signal. So the source resistor provides some negative feedback to hold the amplitude i check.
So it is better to use a bipolar (NPN) transistor, still with an emitter resistor, for a COLPITS oscillator. You can totally ignore what Mr DEMAW claims. His priority was always fast oscillator starting, although he seldom mentioned that.
 
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