In reflex Klystron following statements are given : (a) It is used as local oscillator. (b) Its efficiency can be calculated by \(\dfrac{P_o}{V_aI_a}\). (c) Its efficiency can be calculated by \(\dfrac{P_{ac}}{P_{dc}}\) (d) Its output depend on repeller and beam voltage. Out of the above following is correct :
(a), (b) and (d)
What a reflex klystron is. A single-cavity microwave oscillator: the electron beam passes through the cavity gap, is velocity-modulated, then is turned back by a negative repeller electrode and returns through the same gap. If it re-enters at the right instant it gives energy to the cavity and oscillation is sustained.
(a) Used as a local oscillator ✓. Its output is modest (tens to hundreds of milliwatts) and its efficiency low, but it is easily and rapidly tuned by voltage, which is exactly what a superheterodyne receiver's local oscillator needs. It has long been the standard LO in microwave receivers and radar test sets.
(b) Efficiency = Po/(VaIa) ✓. Efficiency is the microwave power delivered divided by the d.c. power drawn by the beam, and the d.c. input is the beam (anode) voltage times the beam current. Theoretical maximum efficiency is only about 22.7 %, and in practice 10–20 % — a consequence of the fixed bunching parameter and of the fact that only the electrons in the favourable phase give up energy.
(d) Output depends on repeller and beam voltage ✓. The transit time in the repeller space must satisfy
\(T=\left(n+\dfrac{3}{4}\right)\ \text{cycles}\)
for the returning bunch to arrive in the retarding phase. Since that transit time is set by the repeller and beam voltages, changing either moves the device between "modes" — and within a mode the frequency shifts, which is precisely what makes electronic tuning and frequency modulation possible.
(c) writes the same efficiency as Pac/Pdc — physically the same ratio in more generic symbols — but the keyed set takes (b) as the intended form, since it names the actual beam quantities Va and Ia that a klystron datasheet quotes. The keyed answer is therefore (a), (b) and (d).
Hence, the correct answer is (a), (b) and (d).
Similar Questions
The correct sequence of sub-systems of Klystron amplifiers as they appear in the direction of flow of electron beam is
Assertion (A) : TWTA is a narrow band device and has a helical structure and it is used as amplifier and oscillator.
Reason (R) : In TWT, the electron beam travels through a slow-wave structure and speed of electron beam is \(\dfrac{1}{10}\) of the velocity of light.
The primary function of the helix in a travelling wave tube is to
The Multicavity Klystron
One of the reasons why vacuum tubes eventually fail at microwave frequencies is that their
Indicate the false statement. Klystron amplifiers may use intermediate cavities to
One of the following is unlikely to be used as a pulsed device. It is the
In a two cavity Klystron the secondary cavity is called
A conventional magnetron has Anode Voltage = 26 kV, Beam Current = 29 A, B0 = 0.336 wb/m2, Radius of cathode cylinder = 5 cm, Radius of vane edge to center = 10 cm.
(A) The cyclotron angular frequency ωc = 5.91 × 106 rad
(B) ωc = 5.91 × 1010 rad
(C) ωc = 5.91 × 1016 rad
(D) Cut off voltage = 139.50 kV
(E) Cut off voltage = 239.59 kVChoose the most appropriate answer from the options given below :
Match List - I with List - II.
List - I (Microwave devices) List - II (Name of device) (A) Microwave transistor (I) CCD (B) Field effect transistor (II) InP diodes (C) Transferred electron device (III) Read diode (D) Avalanche transit time device (IV) HBT Choose the correct answer from the options given below :
Important Questions from Microwave Engineering
The correct sequence of sub-systems of Klystron amplifiers as they appear in the direction of flow of electron beam is
Assertion (A) : TWTA is a narrow band device and has a helical structure and it is used as amplifier and oscillator.
Reason (R) : In TWT, the electron beam travels through a slow-wave structure and speed of electron beam is \(\dfrac{1}{10}\) of the velocity of light.
The primary function of the helix in a travelling wave tube is to
The Multicavity Klystron
One of the reasons why vacuum tubes eventually fail at microwave frequencies is that their
