17 colpitts ham lesson

Description: The oscillator model discussed in the introduction to oscillators is fundamentally simple, consisting of a capacitor and an inductor. An exploration into oscillator construction led to the discovery of various types of oscillators on a website, which appear straightforward schematically. The focus will be on LC Oscillators, where L represents the inductor and C represents the capacitor. The frequency of oscillation is determined by two capacitors (C1 and C2) arranged in series and connected in parallel to an inductor (L). This configuration forms the tank circuit, where charge oscillates between the capacitor plates, creating an alternating polarity. Capacitors function as voltage dividers, and to access this oscillating loop, a wire connects to a capacitive voltage divider region situated between capacitors C1 and C2. The charge then oscillates through a bipolar junction transistor (BJT), which allows a smaller current to control a larger current. The accompanying images serve as a reference for matching schematic symbols with the BJT electrodes. In the schematic diagrams of the Colpitts Oscillators, all BJTs are NPN types. The emitter electrode of the BJT connects to the capacitive voltage divider region, while the base electrode links to the opposite side of the tank circuit. The collector electrode outputs the amplified signal. The resistor symbol represents any load influenced by the oscillator. The oscillating frequency in the tank circuit is driven by the base electrode, which affects the capacitive voltage divider region and subsequently the emitter electrode. As the charge pulses through the emitter electrode, the collector electrode captures this oscillation and transmits it to the load.

The LC oscillator operates based on the principles of resonance and energy exchange between the inductor and capacitors. The tank circuit, formed by inductor L and capacitors C1 and C2, is crucial for establishing the oscillation frequency, which can be calculated using the formula \( f = \frac{1}{2\pi\sqrt{LC}} \), where \( L \) is the inductance and \( C \) is the equivalent capacitance of C1 and C2. The configuration of these components allows for the oscillation of electrical energy, with the inductor storing energy in its magnetic field and the capacitors storing energy in their electric fields.

The BJT plays a pivotal role in this oscillator circuit by providing the necessary gain to sustain oscillations. The connection of the emitter to the capacitive voltage divider allows for feedback, which is essential for maintaining the oscillation. When the voltage across the capacitors changes, it influences the base current of the BJT, leading to a corresponding change in the collector current. This feedback mechanism ensures that the oscillations are self-sustaining.

In practical applications, the output from the collector can be connected to various loads, such as amplifiers or filters, depending on the desired use of the oscillation signal. The inclusion of a resistor in the output path helps to manage the load and can affect the overall performance of the oscillator, including its amplitude and stability. The careful design of the circuit components and their values is vital for achieving the desired frequency and performance characteristics of the LC oscillator.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 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 load that the oscillator can affect. So what seems to be happening is that the push-pull of the oscillating frequency in the tank circuit could be fueled by the base electrode (everytime it pulls on the base electrode).

That must somehow be affecting the capacitive voltage divider zone which then would affect the emitter electrode. Once the charge pulses its way through the emitter electrode, the collector electrode picks up that oscillation and imposes it on the load.