EST - Microwave - B

Coupling into and out of a traveling-wave tube can be accomplished by:
A. Waveguide match
B. Cavity match
C. Direct coax-helix match
D. All of the above

D
(Explanation: These are all effective methods to ensure efficient transfer of energy in and out of the traveling-wave tube, depending on the specific application and design.)

When it is desired that short-range targets be clearly seen on a pulsed-radar set, it is important that the receiver and display system have:
A. A long time constant
B. Low-pass filters
C. The shortest possible time constant
D. Restricted high-frequency response

C
(Explanation: A shorter time constant reduces smearing and allows the radar to distinguish targets at short distances more accurately.)

The aquadag coating on the inside of a PPI tube is used:
A. To focus the beam of primary electrons
B. To shield the electron beam from unidirectional magnetic fields
C. As a second anode and to prevent the build-up of secondary fields
D. All of these

C
(Explanation: The aquadag coating serves as a secondary anode, improving the tube's efficiency by preventing the accumulation of unwanted charges.)

What allows microwaves to pass in only one direction?
A. RF emitter
B. Capacitor
C. Varactor-triac
D. Ferrite emitter

D
(Explanation: Ferrite materials are used in isolators and circulators to ensure unidirectional propagation of microwaves by utilizing their magnetic properties.)

If the instantaneous RF potentials on the two sides of a magnetron cavity are of opposite polarity, the operation is in the:
A. π mode
B. π/2 mode
C. 2π mode
D. π/4 mode

A
(Explanation: The π mode is the most common operating mode for magnetrons, providing the required phase shift to sustain oscillations.)

Oscillations in a klystron tube are maintained by:
A. Bunches of electrons passing the cavity grids
B. Plate-to-cathode feedback
C. Feedback between the accelerating grid and the repeller
D. Circulating bunches of electrons within the cavities

D
(Explanation: Electrons oscillate within the cavities of a klystron, creating the necessary conditions for amplification and generation of microwave frequencies.)

A PPI cathode-ray tube, as used on a radar set:
A. Is used to check the percentage of modulation
B. Indicates both the range and azimuth of a target
C. Indicates only the range of a target
D. Is used for receiver alignment

B
(Explanation: The PPI (Plan Position Indicator) display is essential for radar systems, as it provides a clear representation of target location relative to the radar station.)

It is possible to increase the maximum range of radar equipment by:
A. Lowering the pulse frequency
B. Raising the peak power of the transmitter
C. Narrowing the beam width and increasing the pulse duration
D. All of these

D
(Explanation: Each method contributes to enhancing the radar's ability to detect distant objects by improving power, resolution, or signal-to-noise ratio.)

A high-power microwave pulse of the order of megawatts can be generated by a:
A. Traveling-wave tube
B. Magnetron
C. Reflex klystron
D. Gunn diode

B
(Explanation: Magnetrons are capable of producing high-power pulses due to their efficient electron bunching and oscillation mechanisms.)

A shipboard equipment which measures the distance between the ship’s bottom and the ocean floor.
A. Fathometer
B. Echosounder
C. LORAN
D. SONAR

D
Explanation: SONAR (Sound Navigation and Ranging) is used to measure underwater distances by emitting sound pulses and detecting their reflections.

Rainfall is an important factor for fading of radio waves at frequencies above
A. 10 GHz
B. 100 GHz
C. 1 GHz
D. 100 MHz

D
Explanation: Rain-induced attenuation becomes significant at frequencies above 10 GHz, affecting signal strength.

In a pulsed radar set, the STC circuit is used to
A. Improve the target bearing resolution
B. Increase receiver sensitivity for echoes from targets
C. Vary the pulse frequency to control the maximum target
D. Reduce interference from the effects of sea return

D
Explanation: Sensitivity Time Control (STC) reduces receiver gain for close targets, minimizing sea clutter interference.

Which causes multipath or frequency selective fading?
A. Small reflector
B. Nearer reflector
C. Further reflector
D. Large reflector

D
Explanation: Large reflectors can cause multiple signal paths, leading to interference and frequency-selective fading.

If k-factor is greater than 1, the array beam is bent
A. Away from the earth
B. Towards the ionosphere
C. Towards the earth
D. Towards outer space

C
Explanation: A k-factor greater than 1 indicates super-refraction, causing the radio wave to bend towards the earth.

Klystron oscillators are most often used in the frequency range of
A. 300 to 3000 MHz
B. 3000 to 30000 MHz
C. 30 to 30000 MHz
D. 10 to 10000 MHz

B
Explanation: Klystrons are commonly used in the super high frequency (SHF) range, from 3 to 30 GHz.

Which of the following permits a microwave signal to travel in one direction with virtually no loss, but severely attenuates any signal attempting to travel in the reverse direction?
A. Isolator
B. Wave trap
C. Tunnel diode
D. Circulator

A
Explanation: An isolator allows unidirectional signal flow, protecting components from reflected power.

The main frequency determining element of a klystron is
A. The repeller voltage
B. The accelerating voltage
C. Its resonant cavity
D. Its mode of operation

C
Explanation: The resonant cavity's dimensions and properties set the klystron's operating frequency.

As the electron beam moves through a klystron’s intercavity drift space
A. Frequency modulation at the input cavity creates velocity modulation at the output cavity
B. Velocity modulation at the input cavity creates density modulation at the output cavity
C. Density modulation at the input cavity creates velocity modulation at the output cavity
D. Phase modulation at the input cavity creates velocity modulation at the output cavity

B
Explanation: Velocity modulation in the input cavity leads to electron bunching, resulting in density modulation at the output.

In a pulsed radar set, the function of the duplexer is to
A. Aid in calibrating the display unit
B. Prevent frequency drift in the klystron
C. Allow the transmitter and the receiver to operate from a common antenna
D. All of these

C
Explanation: The duplexer switches between transmitting and receiving modes, enabling shared antenna use.

The antenna separations (in meters) required for optimum operation of a space diversity system can be calculated from: S=2λRLS = \frac{2\lambda R}{L}S=L2λR​, where RRR is the effective earth radius (m) and LLL is the path length (m).
A. S=2λRLS = \frac{2\lambda R}{L}S=L2λR​
B. S=3λRLS = \frac{3\lambda R}{L}S=L3λR​
C. S=λRLS = \frac{\lambda R}{L}S=LλR​
D. S=LλRS = \frac{L}{\lambda R}S=λRL​

B Explanation: This formula ensures that the antennas are optimally separated to avoid interference and achieve diversity gain in a communication system.