17 colpitts ham lesson

Posted on Feb 5, 2014

The oscillator model I talked about in the introduction to oscillators was as simple as it gets - capacitor + inductor. So I wanted to try to make my own oscillator. In a search for how to make an oscillator  I got a website with a few different kinds. They look pretty simple  schematically, but I like to know how the charge is travelling thro

17 colpitts ham lesson
Click here to download the full size of the above Circuit.

ugh the actual circuits. I should also preface this by saying that the oscillators I will be going through are known as LC Oscillators (L stands for Inductor, C stands for Capacitor) or Inductor-Capacitor Oscillators. So here goes! Two capacitors (C1 and C2) in series and parallel to one inductor (L) determine the frequency of oscillation. These are also what make up the tank circuit (if you remember the tank circuit was where the charge would go back and forth from capacitor plate to capacitor plate and thus have an oscillating polarity). Capacitors, like resistors, are voltage dividers and to tap into this oscillating loop, a wire would connect to a capacitive voltage divider  region located between capacitors C1 and C2. The charge is then able to pulsate through a BJT (bipolar junction transistor) which if you remember from a few articles ago - allows a smaller current to control a larger current. The reason I put all of these pictures up is to help me remember how the schematic symbols matched with the different electrodes of the BJT. Now based on the schematic diagrams of the Colpitts Oscillators, the BJTs are all NPNs. The emitter electrode of the BJT seems to be connected to the capacitive voltage divider region and the base electrode of the BJT is connected to the other side of the tank circuit. The collector electrode is then what sends the output of the amplified signal out. The resistor symbol represents any...

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