What is an electronic oscillator? It’s an electronic device that produces a sine wave or a square wave. Oscillators are used in transceivers to modulate a signal and are used in receivers to demodulate an incoming signal and to tune the radio to the desired frequency.
An easy way to create an electronic oscillator is by charging a capacitor and then adding an inductor into the circuit. Both capacitors and inductors are two electrical components that hold charge. A capacitor uses an electrostatic field whereas the inductor uses a magnetic field.
When the capacitor is charged up by a battery or other power source, the capacitor will then start to slowly discharge and that moving current will go through the inductor which will create a magnetic field. The inductor keeps the current flowing which eventually goes all the way around the circuit and charges up the other side of the capacitor. The current flow moves like this back and forth which creates the oscillating function.
We talked about how current through an electric oscillator moves back and forth through the circuit. This is what produces a sinusoidal wave. Modulating oscillators are sometimes known as low-frequency oscillators.
Low-frequency oscillators are set to a sub audible frequency and are used to modulate the signal coming from another oscillator of a tone we do want to hear. Remember that super low frequencies travel a lot farther than high frequencies so when we modulate a signal it is able to travel a lot farther.
Resonators and Demodulation
Your HAM radio antenna actually sees thousands of different waves up in the air every day, so how does it know which one to pick up on? Different antennas are designed to pick up on certain ranges of frequencies but still how does it know which particular frequency to hone in on? The answer is the resonator inside of your receiver.
When you are adjusting your radio to a desired frequency, what you are actually doing is adjusting a varying capacitor inside your receiver’s circuitry. The resonant frequency is the frequency that will be picked up by the circuit and is determined by the ratio of capacitance and inductance. This formula calculates resonant frequency: f = 12LC
So when you tune your circuit to a particular frequency then only that frequency is picked up and amplified when all the other frequencies get ignored by the circuit. The current is traveling back and forth through the circuit at the resonant frequency or the frequency you are wanting to listen to.
After the oscillator has picked up the resonant frequency, the process of demodulation occurs. This happens by filtering out the unwanted carrier frequency to get the signal back to the desired audio signal.
Types of Oscillators
There are several different kinds of oscillators. A few of the more popular ones include RC oscillators, LC oscillators and crystal oscillators. These are all examples of feedback oscillators that are more commonly found in radio.
An RC oscillator is a circuit that is constructed from resistors and capacitors for oscillation function. RC oscillators are known to produce lower frequencies. To find the resonant frequency of this circuit, the equation is f = 12RC.
The LC oscillator (mentioned above), consists of a combination of an inductor and a capacitor that work together to create an oscillating signal from a tuned circuit. Some examples of this type of circuit design include Hartley, Colpitts and Clapp circuits.
The crystal oscillator uses a quartz crystal which works as the resonator itself. Crystals work better with higher temperatures than tuned circuits which make them more stable for a variety of frequencies. Because of this crystal oscillators are the most popular kind of oscillators for radio transmitters.
There are different kinds of electronic oscillators but they all do pretty much the same thing. They can modulate a signal, pick up a signal and demodulate the signal. There are different ways to find the resonant frequency.
The crystal oscillator is the most popular method for radio transmitters. They work similarly to a LC oscillator, the only difference is the tuned circuit is replaced with a crystal.