Klystron Oscillator
Microwave Tubes || Reflex Klystron Oscillator What is a Klystron Amplifier ? https://youtu.be/dr5dc19w8CY Here it is the Notes of Klystron Oscillator : A Klystron tube is generated the microwave frequencies, this can be used as an amplifier or an oscillator of the microwave signals. Need of Reflex Klystron Oscillator : We know a two cavity klystron acts as an amplifier to provide amplification of RF signals. Basically it can be converted into an oscillator, but some disadvantages are associated with it. Hence the same structure cannot be utilised for generating oscillations. As we know to design an oscillator, positive feedback must be provided to the input in a way to have a magnitude of loop gain as unity. So, if we design a Klystron oscillator using two cavity klystron then to have a change in oscillating frequency and resonant frequency of the two cavities. Thereby leading to cause difficulty in generating oscillations. Thus to overcome this problem a Reflex klystron was introduced. Operating principle of Reflex Klystron : The Reflex klystron is a single cavity variable frequency micro wave generator of low power and low efficiency and it is used to produce sustained oscillations at microwave frequencies. Its principle of operation is velocity and current modulation. The variation in the velocity of electrons while inside the tube is known as "Velocity Modulation". A transfer of power from a source of DC voltage to a source of AC voltage is known as "Current Modulation". Construction of Reflex Klystron : It is basically a vacuum glass tube. Many sections are present in the tube, those are electron gun, cavity resonator, repeller and output coupling. The structure consists of an electron gun, which is used to generates the electron flow and acting as a cathode. The repeller electrode is present at the opposite end of the electron gun and it is connected with a negative voltage and it reflects the electron beam back to the resonator cavity. It consists of only a single cavity and act as a Buncher as well as Catcher cavity separately. At the time of forward movement of the electron beam act as a "Buncher cavity" while at the time of backward movement it is a "Catcher cavity" and it is take as the anode. This structure uses two voltages in which repeller voltage which is connected to repeller and consists of negative potential. And another is anode voltage which is connected to the single cavity and consists of positive charge of the battery. Working of Reflex Klystron : Initially when the electron beam is emitted by the electron gun with a very high velocity. After passing the gap in the cavity, electrons travel towards a repeller electrode which is at a high negative potential. The electrons never reach the repeller because of the negative field and are returned back towards the gap. So the velocity modulated electrons must have to travel a backward path inorder to provide feedback. Therefore, at the time of returning, the bunched electrons transfers the maximal of their energy to the catcher cavity. Thereby leading to cause sustained oscillations inside the tube. For oscillations to be sustained, the time taken by the electrons to travel into the repeller space and back to the gap called "Transist time". When the externally applied potential is very high, then electron gun emits the electrons with a very high velocity. These electrons are generally known as "Early electrons". But when the externally applied potential is almost zero, then electrons moves with uniform velocity with which it was emitted by the electron gun and these are known as "Reference electrons". Further the electrons that is emitted by the electron gun after reference electrons experiences highly negative potential at the cavity and moves with very low velocity inside the tube. These are known as "Late electrons". This change in velocity of moving electrons is known as "Velocity modulation" and due to this all the electrons get bunched while returning towards the catcher cavity. So, in this way bunch of electrons reaches the catcher cavity. This bunch of electrons leads to cause "Current modulation" inside the tube. Bunching Process represented by Applegate Diagram : The process of bunching involves in the return journey of all the three categories of electrons i.e., Early, Reference and Late electrons. Here the X - axis represents the time and Y - axis shows the distance travelled by the electrons inside the tube. As we have already discussed that bunching takes place at the time of return journey of electrons. In case of early electrons, due to high velocity, they require greater time to repel back towards the catcher cavity. Due to uniform velocity of reference electrons, they get repelled by the repeller in a lesser time than the early electrons. And we know the velocity of late electrons is very low and they took minimal amount of time to get repelled back. Thank you for watching this video & Share with your friends
Microwave Tubes || Reflex Klystron Oscillator What is a Klystron Amplifier ? https://youtu.be/dr5dc19w8CY Here it is the Notes of Klystron Oscillator : A Klystron tube is generated the microwave frequencies, this can be used as an amplifier or an oscillator of the microwave signals. Need of Reflex Klystron Oscillator : We know a two cavity klystron acts as an amplifier to provide amplification of RF signals. Basically it can be converted into an oscillator, but some disadvantages are associated with it. Hence the same structure cannot be utilised for generating oscillations. As we know to design an oscillator, positive feedback must be provided to the input in a way to have a magnitude of loop gain as unity. So, if we design a Klystron oscillator using two cavity klystron then to have a change in oscillating frequency and resonant frequency of the two cavities. Thereby leading to cause difficulty in generating oscillations. Thus to overcome this problem a Reflex klystron was introduced. Operating principle of Reflex Klystron : The Reflex klystron is a single cavity variable frequency micro wave generator of low power and low efficiency and it is used to produce sustained oscillations at microwave frequencies. Its principle of operation is velocity and current modulation. The variation in the velocity of electrons while inside the tube is known as "Velocity Modulation". A transfer of power from a source of DC voltage to a source of AC voltage is known as "Current Modulation". Construction of Reflex Klystron : It is basically a vacuum glass tube. Many sections are present in the tube, those are electron gun, cavity resonator, repeller and output coupling. The structure consists of an electron gun, which is used to generates the electron flow and acting as a cathode. The repeller electrode is present at the opposite end of the electron gun and it is connected with a negative voltage and it reflects the electron beam back to the resonator cavity. It consists of only a single cavity and act as a Buncher as well as Catcher cavity separately. At the time of forward movement of the electron beam act as a "Buncher cavity" while at the time of backward movement it is a "Catcher cavity" and it is take as the anode. This structure uses two voltages in which repeller voltage which is connected to repeller and consists of negative potential. And another is anode voltage which is connected to the single cavity and consists of positive charge of the battery. Working of Reflex Klystron : Initially when the electron beam is emitted by the electron gun with a very high velocity. After passing the gap in the cavity, electrons travel towards a repeller electrode which is at a high negative potential. The electrons never reach the repeller because of the negative field and are returned back towards the gap. So the velocity modulated electrons must have to travel a backward path inorder to provide feedback. Therefore, at the time of returning, the bunched electrons transfers the maximal of their energy to the catcher cavity. Thereby leading to cause sustained oscillations inside the tube. For oscillations to be sustained, the time taken by the electrons to travel into the repeller space and back to the gap called "Transist time". When the externally applied potential is very high, then electron gun emits the electrons with a very high velocity. These electrons are generally known as "Early electrons". But when the externally applied potential is almost zero, then electrons moves with uniform velocity with which it was emitted by the electron gun and these are known as "Reference electrons". Further the electrons that is emitted by the electron gun after reference electrons experiences highly negative potential at the cavity and moves with very low velocity inside the tube. These are known as "Late electrons". This change in velocity of moving electrons is known as "Velocity modulation" and due to this all the electrons get bunched while returning towards the catcher cavity. So, in this way bunch of electrons reaches the catcher cavity. This bunch of electrons leads to cause "Current modulation" inside the tube. Bunching Process represented by Applegate Diagram : The process of bunching involves in the return journey of all the three categories of electrons i.e., Early, Reference and Late electrons. Here the X - axis represents the time and Y - axis shows the distance travelled by the electrons inside the tube. As we have already discussed that bunching takes place at the time of return journey of electrons. In case of early electrons, due to high velocity, they require greater time to repel back towards the catcher cavity. Due to uniform velocity of reference electrons, they get repelled by the repeller in a lesser time than the early electrons. And we know the velocity of late electrons is very low and they took minimal amount of time to get repelled back. Thank you for watching this video & Share with your friends