Subject: RADIO UNIT I
BASIC PRINCIPLES OF SWING
The definition of rock is fluctuating between two states and conditions:
Swinging is vibrating or change from one state to another state.
An oscillator is a device that produce oscillations in the form of repetitive waves.
An oscillator is an electronic circuit used in electronic communications as frequency generator to transmit signals between a transmitter and a receiver.
an oscillator in electronic applications is a device or circuit that produces oscillations power.
A power swing is a repetitive change of voltage or current waveform.
If an oscillator is self sustained, changes in the waveform is continuous and repetitive.
A self-sustained oscillator circuit does not require a input signal for its operation, it is generating its own electronic signal.
can say that the only signal that is applied to an oscillator is a DC voltage (bias voltage) to operate.
An oscillator in an electronic circuit from a dc voltage generates a voltage as BC sine wave.
2 .- OSCILLATORS FEEDBACKS
oscillators to function properly must have a feedback loop.
feedback in electronic means take a portion of the output signal and return to the entrance.
Figure 1 shows an example of the principle of feedback.
feedback is to send a voltage or current output to the input.
Fig. 1 Model of a feedback amplifier
The feedback loop is physically an electrical connection made by a cable.
electronics exist in two types of feedback:
Feedback
positive negative feedback
In oscillator circuits using the positive feedback.
There are four requirements that must be met to achieve a good performance in an oscillator:
1.1 .- Amplification: an oscillator must have an amplifier capable of amplifying voltage.
1.2 .- Positive feedback: An oscillator circuit must have a complete path for the output signal back to the entrance.
feedback signal must be regenerated, that means that you must have the correct phase and amplitude correct. (*) 1.3 .-
to determine the frequency components: An oscillator must determine the frequency components such as resistors, capacitors, coils or crystals that allow to set or change the operating frequency. 1.4 .-
Power: An oscillator to operate like any other electronic circuit requires a power supply.
To produce self-sustained oscillations, an oscillator circuit must meet four basic requirements described above.
The most common configurations used in an oscillator for its operation are: RC (Resistance-Capacitor)
LC (coil-capacitor), the quartz crystals and integrated circuits.
3 .- TANK CIRCUIT
In an electronic oscillator which aim is to obtain an oscillating system which is stable and regular, maintaining a frequency and a continuous waveform.
This natural process takes advantage of possessing the damped oscillation circuits composed of elements capacitive or inductive .
These elements have the ability to store electrical charge inside (electrically charged) and unloaded when the load of food has gone.
The simplest example of oscillator is composed of a coil, a capacitor, a battery and a switch.
This circuit is called tank circuit.
Figure 2 describes the tank circuit
Fig. 2
Initially the switch is left in place so that the capacitor C is charged with providing battery power V.
After some time the switch is passed to the right position. As the coil has no load and the capacitor is fully charged, the latter is fully discharged into the coil, once the capacitor is completely discharged now winding which is downloaded onto the
capacitor, not standing until the load on the coil is zero and therefore the capacitor is again charged.
This process is repeated until the stored energy is consumed either as heat.
This process can be plotted using an XY Cartesian axis in the x-axis represents time and the y-axis value of the electric current flowing through the coil and the voltage at the terminals of the capacitor.
If you draw it we can see how there is a continuous exchange of energy between the capacitor and coil.
The subtraction of energy produced by the resistance of the inductor and capacitor (which can overheat the components) is what makes this process is not infinite.
Fig. 3 curves LC oscillator
In the graph we can see how the gap voltage between terminals of the coil is always in effect opposite to that in the condenser.
This lag is 180 ° between strains, there is a gap of 90 ° between the current flowing through the coil and tension.
This signal is buffered to the time until become extinct after a relatively short time period. An electronic circuit that is capable of reloading electrically one component will make a consistent swing
process.
oscillation frequency
The characteristic of this type of circuit, also known as LC tank circuit is that the speed with which current flows and returns from the condenser coil or vice versa, occurs with a frequency
where:
F is measured in Hertz, C in Farads and L in henry .
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