it generates the carrier frequency of the output after passing a signal.
There are several methods for generating FM signals but they all basically involve an oscillator with an electrically adjustable frequency. This type of oscillator uses an input voltage to affect the frequency of its output. For example, when the applied voltage increases, the oscillator output frequency increases and when the applied voltage decreases, the oscillator output frequency decreases as well. If no voltage is applied to the oscillator its output will be a signal at its centre frequency. The amount of frequency variations is deviated around the oscillators' centre frequency.
An amplifier can become and oscillator by adding positive feedback from the output back to the input. Positive feedback means that the phase of the signal fed back to the input is the same as the phase of the output signal. In the case of a high frequency oscillator, a tuned circuit (inductor and capacitor) or a quartz crystal in the input circuit will determine the frequency of oscillation.
Oscillator is a generic word for any circuit that produces an alternative signal. The shape of the signal, its stability and its output impedance are not considered in this case. "Local oscillator" is one specific type of oscillator used in radio receiver for the purpose of frequency conversion. the input Radio Frequency( RF ) signal is "mixed" with the local oscillator signal and the subtraction of two frequencies is obtained at the output. "Mixing" in this context means: "multiplication"\ In some other context in electronics (specially audio) mixing means "adding" the mathematical operation for local oscillator is F out=Fin - F loc.osc. The output of the mixing operation can also be Fin+F loc.Osc. But this higher frequency is usually filtered out. The local oscillator needs to be a pure sine wave with a very good frequency stability and usually very stable output voltage. Recently very good "synthesizers" are introduced in the market that permit generation "programmable local oscillation"
Mix it with a local oscillator whose frequency is (the IF frequency) away from the frequency of the FM signal you're interested in.
The output of the voltage-controlled oscillator (VCO) in a phase-locked loop (PLL) circuit is a periodic waveform, typically a sine or square wave, whose frequency is controlled by the input voltage. This voltage is derived from the phase comparator in the PLL, which adjusts the VCO frequency to match the frequency of a reference signal. As the PLL locks onto the reference signal, the VCO output frequency stabilizes, ensuring that it is phase-locked with the reference. This output can be used for various applications, including frequency synthesis and modulation.
Trasmitting stations have their own transmitting frequency. No one can construct an amplifier which amplifies signals over a wide range. So every transmitting frequency has to be changed to one particular frequency. This is known as INTERMEDIATE frequency (IF) This is quite possible by getting beats. So a signal is to generated whose frequency is just more than the incoming frequency by IF This signal is named as local singnal which is generated by the LOCAL oscillator.
A local oscillator is an electronic device used to generate a signal normally for the purpose of converting a signal of interest to a different frequency using a mixer. This process of frequency conversion, also referred to as heterodyning, produces the sum and difference frequencies of the frequency of the local oscillator and frequency of the input signal of interest. These are the beat frequencies. Normally the beat frequency is associated with the lower sideband, the difference between the two.
To calculate the intermediate frequency (IF) for a radio receiver at 70 MHz, you typically choose a fixed IF value such as 455 kHz or 10.7 MHz. The IF frequency is chosen in such a way that when the desired signal frequency (70 MHz) is mixed with the local oscillator signal, it falls within the receiver's bandwidth for demodulation. This allows for effective filtering and processing of the signal at a manageable frequency before demodulation.
There are many different types of oscillator circuits, the majority of which use positive feedback.
Some disadvantages of Hartley oscillator include lower frequency stability compared to other oscillator configurations, sensitivity to variations in component values and external factors, and the potential for higher harmonic content in the output signal. Additionally, the design and tuning of a Hartley oscillator can be more complex compared to simpler oscillator configurations.
Low frequency signal are not able to get propagated throught longer distance. So it is to be carried by a carrier wave. Hence high frequency carrier wave is to be generated by the help of an oscillator. So we need an oscillator here a crystal oscillator to produce high frequency carrier waves.