# Hartley And Colpitts Oscillators Pdf

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*The Hartley oscillator is an electronic oscillator circuit in which the oscillation frequency is determined by a tuned circuit consisting of capacitors and inductors , that is, an LC oscillator. The circuit was invented in by American engineer Ralph Hartley. The distinguishing feature of the Hartley oscillator is that the tuned circuit consists of a single capacitor in parallel with two inductors in series or a single tapped inductor , and the feedback signal needed for oscillation is taken from the center connection of the two inductors.*

- Hartley oscillator
- 7 Hartly & Collpit PDF
- Design and Fabrication of LC-Oscillator Tool Kits Based Op-Amp for Engineering Education Purpose

## Hartley oscillator

To study and calculate frequency of oscillations of Hartley oscillator. Compare the frequency of oscillations, theoretically and practically. Hartley oscillator is very popular and is commonly used as a local oscillator in radio receivers. It has two main advantages viz Adaptability to wide range of frequencies and easy to tune. The tank circuit is made up of L1, L2, and C1.

The coil L1 is inductively coupled to coil L2, the combination functions as auto transformer. The resistances R2 and R3 provide the necessary biasing. The capacitance C2 blocks the d. The frequency of oscillations is determined by the values of L1, L2 and C1 and is given by,. The energy supplied to the tank circuit is of correct phase. The auto transformer provides out of phase.

Also another is produced. By the transistor. In this way, energy feedback to the tank circuit is in phase with the generated oscillations. The Hartley oscillator is one of the simplest and best-known oscillators and is used extensively in circuits, which work at radio frequencies. Figure 1 shows the basic Hartley oscillator circuit configuration.

The transistor is in voltage divider bias, which sets up Q-point of the circuit. The output voltage is fed back to the base and sustains oscillations developed across the tank circuit, provided there is enough voltage gain at the oscillation frequency.

The Hartley oscillator is an LC electronic oscillator that derives its feedback from a tapped coil in parallel with a capacitor the tank circuit. Although there is no requirement for there to be mutual coupling between the two coil segments, the circuit is usually implemented as such. A Hartley oscillator is essentially any configuration that uses a pair of series-connected coils and a single capacitor.

Hartley oscillator is similar to Colpitts oscillator with minor modification. Instead of using tapped. The tank circuit is made up of L1, L2 and C. Circuit Operation : When the circuit is turned on, the capacitance is charged. When this capacitance is fully charged, it discharge through coils L1 and L2 setting up oscillations of frequency determined by experiment 1. The output voltage of the amplifier appears across L1 and feedback voltage across L2.

The voltage across L2 is out of phase with the voltage developed across L1 Vout as shown in figure 1. It is easy to see voltage fed back i. A phase shift of is produced by L1-L2 voltage divider. In this way, feedback is properly phased to produce continuous undamped oscillations. Feedback fraction in Hartley oscillator, the feedback voltage is across L2 and output voltage is across L1.

In Hartley oscillator the circulating current passes through the series combination of L1 and L2. The coefficient of coupling gives the extent to which two inductors are couple.

The feedback should be enough to start oscillations under all conditions as different transistor, temperature, voltage, etc. Either changing the value of inductor can change the resonant frequency or changing the value of capacitor but the combination of the three components should satisfy the above given two conditions for oscillation. Advantages of the Hartley Oscillator: 1.

The frequency is varied using a variable capacitor. The output amplitude remains constant over the frequency range. The feedback ratio of the tapped inductor remains constant. Disadvantages : 1.

Harmonic-rich content of the output. It is not suitable for a pure sine wave. Connect terminals a and b together. Similarly connect d and Gnd together. Switch on the mains supply. Connect oscilloscope between Vout TP4 and Gnd. If you want to check the unfiltered output waveform, you may observe the signal on TP3 also.

Measure the value of output frequency on oscilloscope. Record it into the observation table. Calculate the resonance frequency theoretical using equation 1. Compare measured frequency with the theoretically calculated value.

Switch "off the supply. Remove the patch cord connected between terminals a and b and connect it between a and c. Similarly remove the patch cord connected between terminals d and Gnd and connect it between e and Gnd. Follow the procedure from step 5 to All the connections should be correct.

Terminals must be identified properly. Reading should be taken without any parallax error. Frequency of oscillations of Hartley Oscillator is measured practically and campared with theoritical values. No external input is required except for the DC operating voltage. To sustain oscillations at a given frequency, the three main requirements of an oscillator is: Amplification Regenerative feedback A resonant circuit Hartley oscillators generate a sine wave output and use split inductors.

The output frequency of the Hartley oscillator can be varied by changing component values in the resonant circuit. The power requirements for transistor oscillators are low. Oscillators are normally operated Class C for maximum efficiency. The series-fed Hartley oscillator has DC current flow through part of the resonant circuit. The shunt-fed Hartley oscillator does not have DC current flow in the resonant circuit. Base leak bias makes the Hartley oscillator self starting.

Base leak bias is self adjusting to the amplitude of oscillations. The tank circuit is made up of L1,C4 and C5. The resistance R2 and R3 provides the necessary biasing. The capacitance C2 blocks the D.

C component. The tank circuit provides out of phase. Also the transistor provides another 0. The Colpitt oscillator is one of the simplest and best-known oscillators and is used extensively in circuits, which work at radio frequencies. Figure 3 shows the basic Colpitt oscillator circuit configuration. In the circuit note that Vout is actually the AC voltage across C2.

This voltage is feed back to the base and sustains oscillations developed across the tank circuit, provided there is enough voltage gain at the oscillation frequency. It uses two capacitors C1 and C2 placed across a common inductor L and the center of the two capacitor is tapped. The tank circuit is made up of C1 and C2 and L.

When the circuit is turned on, the capacitors C1 and C2 are charged. The capacitor discharge through L, setting up oscillations of frequency determined by experiment 1.

The output voltage of the amplifier appears across C1 and feedback voltage is developed across C2. The voltage across C2 isout of phase with the voltage developed across C1 Vout as shown in figure 3. It is easy to see that voltage feedback voltage across C2 to the transistor provides positive feedback. The transistor and a further phase shift of is produced by C1-C2 voltage divider produce a phase shift of In this way, feedback is properly phased to produce continuous undamped oscillation.

Feedback fraction MV :The amount of feedback voltage in colpitts oscillator depend upon feedback fraction MV of the circuit. For this circuit Feedback fraction:. Because, the circulating current for the two capacitors is the same further, capacitive reactance is inversely proportional to capacitance. Connect terminals a and b and similarly d and Gnd together. Connect oscilloscope between Vout and Gnd on NV board.

Switch off the supply. Remove the patch cord connected between terminals a and b, and connect it between a and c. Remove the patch cord connected between terminals d and Gnd and connect it between e and Gnd.

Follow the procedure from point 4 to 9. Capacitors Ceq.

## 7 Hartly & Collpit PDF

A Colpitts oscillator looks just like the Hartley oscillator but the inductors and capacitors are replaced with each other in the tank circuit. The constructional details and operation of a colpitts oscillator are as discussed below. The resistors R 1 , R 2 and R e provide necessary bias condition for the circuit. The capacitor C e provides a. This also provides temperature stabilization. The capacitors C c and C b are employed to block d.

An oscillator is used to produce electronic signal with oscillating periods. Eg: Sine wave, square wave etc.. Oscillators are broadly classified into two — linear oscillators and non-linear oscillators. As the name implies, linear oscillators are used to produce linear or sinusiodal waveforms. Whereas, non-linear oscillators are used to produce non-linear non-sinusoidal output waveforms. All types of electronic oscillators use their input voltage to control the oscillation frequency. Colpitts Oscillator is an electronic oscillator which uses an inductor and capacitors to form an LC oscillator circuit.

## Design and Fabrication of LC-Oscillator Tool Kits Based Op-Amp for Engineering Education Purpose

The electronic circuit that produces periodically oscillating electronic signal such as sine wave, square wave or any other wave is termed as Electronic Oscillator. Oscillators can be classified into different types generally based on their output frequency. Electronic oscillators can be termed as voltage controlled oscillators as their frequency of oscillations can be controlled by their input voltage. Foremost electronic voltage controlled oscillators can be considered as two types namely: Linear Oscillator and Nonlinear Oscillator.

Each has a resonant circuit that is connected in the same place. The only difference is that the tap on the resonant circuit is implemented with the capacitors in the Colpitts and an inductor tap in Hartley. One outcome of the inductor tap is that the Hartley has some tendency to have parasitic resonances as the inductor is divided by the tap into two parts, and the mutual inductance between them has a final value.

A very popular local oscillator circuit that is mostly used in radio receivers is the Hartley Oscillator circuit. The constructional details and operation of a Hartley oscillator are as discussed below. In the circuit diagram of a Hartley oscillator shown below, the resistors R 1 , R 2 and R e provide necessary bias condition for the circuit. The capacitor C e provides a. This also provides temperature stabilization.

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## 2 Comments

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Clementine L.To study and calculate frequency of oscillations of Hartley oscillator.