As we know in klystron tube drift space is assumed to be free of any electric field. Therefore, the high velocity electron emerging in the later period are able to overtake the low velocity electrons leaving the buncher grids. As a result of these actions, the electrons gradually bunch together as they travel down the drift space. This mechanism of variation in electron velocity in the drift space is known as velocity modulation.
the microwave tubes that undergoes velocity modulation are klystron tubes ie, two cavity klystron.....
The process whereby a time varn in vel is impressed upon the beam of el is called vel modulation.
tery ma ki chut bhan k lode gandu
klystron can act as both an amplifier and oscillator whereas a reflex klystron can act as only an oscillator. klystron needs a buncher cavity(sometimes multiple bunchers) and a catcher cavity whereas a reflex klystron needs only one cavity. klystron bunches electrons in forward direction, whereas the other bunches in the reverse direction using a reflector plate. klystron needs i/p signal (accelerating or deccelerating potential) whereas the other dont.
in twt electrons are constant with rf field for long time&in klystron for short time. in klystron electron constant with r.f field with long time& in twtare shot time.
the microwave tubes that undergoes velocity modulation are klystron tubes ie, two cavity klystron.....
The process whereby a time varn in vel is impressed upon the beam of el is called vel modulation.
due to velocity modulation density modulation occurs in TWT
As we know normal modulation is superimposing the wave with another carrier signal but the concept of velocity modulation is totally different, as The modulation in velocity of a beam of electrons or ions caused by passing the beam through a high-frequency electric field, as in a cavity resonator there is no concept of superimposition.
The power gain of a two cavity klystron amplifier is about 30 dB. In order to achieve higher overall gain, one way is to connect several two-cavity tubes in cascade, feeding the output to each of the tubes to the input of the following one. Besides using the multistage techniques, the tube manufacturers have designed and produced multi cavity klystron to sere the high-gain requirement. In a multi cavity klystron each of the intermediate cavities, placed at a distance of the bunching parameter X of 1.841 away from the previous cavity, acts as a buncher with the passing electron beam inducing a more enhanced RF voltage than the previous cavity, which in turn sets up an increased velocity modulation.
The Reflex Klystron:Another tube based on velocity modulation, and used to generate microwave energy, is the REFLEX KLYSTRON. The reflex klystron contains a REFLECTOR PLATE, referred to as the REPELLER, instead of the output cavity used in other types of klystrons. The electron beam is modulated as it was in the other types of klystrons by passing it through an oscillating resonant cavity, but here the similarity ends. The feedback required to maintain oscillations within the cavity is obtained by reversing the beam and sending it back through the cavity. The electrons in the beam are velocity-modulated before the beam passes through the cavity the second time and will give up the energy required to maintain oscillations. The electron beam is turned around by a negatively charged electrode that repels the beam. This negative element is the repeller mentioned earlier. This type of klystron oscillator is called a reflex klystron because of the reflex action of the electron beam. Check out the link below for more information.
a. velocity modulated tube b. frequency modulated tube c. Amplitude modulated tube d. simple triode
tery ma ki chut bhan k lode gandu
klystron can act as both an amplifier and oscillator whereas a reflex klystron can act as only an oscillator. klystron needs a buncher cavity(sometimes multiple bunchers) and a catcher cavity whereas a reflex klystron needs only one cavity. klystron bunches electrons in forward direction, whereas the other bunches in the reverse direction using a reflector plate. klystron needs i/p signal (accelerating or deccelerating potential) whereas the other dont.
What is probably the primary advantage of the reflex klystron over the two-cavity klystron is the mechanism used to tune the device. The two-cavity klystron has mechanical tuning, but the reflex klystron is tuned electrically. And it doesn't take an electrical engineering degree for an investigator to figure out that electrical controls can be manipulated a whole bunch faster than a mechanical device.
in twt electrons are constant with rf field for long time&in klystron for short time. in klystron electron constant with r.f field with long time& in twtare shot time.
A: It is a microwave oscillator device.