Microwave MCQ Flashcards
the progressive decrease in signal strength with increasing distance
Attenuation
if k-factor is greater than 1, the beam is bent …
towards the earth
The antenna separations (in meters) required for optimum operation of a space diversity system can be calculated from:
S = 3λR/L
where R = effective earth radius (m) and L = path length (m)
Rainfall is an important factor for fading of radio waves at frequencies above
10 GHz
Theoretically electromagnetic radiation field strength varies in inverse proportion to the square of the distance, but when atmospheric attenuation effects and the absorption of the terrain are taken into account the attenuation can be as high as the inverse _______ power of the distance.
Sixth
What do you call an attenuation that occurs over many different wavelengths of the carrier?
Slow fading
Which of the reception problems below that is not due to multipath?
Slow fading
Which causes multipath or frequency-selective fading?
Large reflector
In microwave transmission using digital radio, what causes most intersymbol interference?
Delayed spreading
A shipboard equipment which measures the distance between the ship’s bottom and the ocean floor.
SONAR
The cavity resonator
Is equivalent to an LC resonant circuit
a high-power microwave pulse of the order of megawatts can be generated by
magnetron
What is the purpose of the electromagnetic field which surrounds a traveling-wave tube?
To keep the electrons from spreading out
Which of the following is used as an oscillator device in the SHF band?
Tunnel diode,
Klystron tube
Microwave frequencies are normally regarded as those in the range
1 to 100 GHz
The highest frequency which a conventional vacuum-tube oscillator can generate is not limited by the
Degree of emission from the cathode
As the electron beam moves through a klystron’s intercavity drift space
Velocity modulation at the input cavity creates density modulation at the output cavity
The frequency of the oscillation generated by a magnetron is mainly determined by
The dimension of each cavity resonator
If the instantaneous RF potentials on the two sides of a magnetron cavity are of opposite polarity, the operation is in
π mode
The Gunn diode oscillator
Depends on the formation of charge domain
What ferrite device can be used instead of a duplexer of an isolated microwave transmitter and receiver when both are connected to the same antenna?
Circulator
To achieve good bearing resolution when using a pulsed-radar set, an important requirement is
A narrow antenna-beam width in the horizontal plane
When used in conjunction with a radar set, the purpose of an echo box is to provide an artificial target
Which may be used to tune the radar receiver
In a radar-set receiver, the usual mixer stage is
A silicon crystal
Klystron oscillators are most often used in the frequency range of
3000 to 30000 MHz
Oscillators of a klystron tube are maintained
By bunches of electrons passing the cavity grids
What allows microwaves to pass in only one direction?
Ferrite emitter
In an SHF pulsed radar set, a reflex klystron can be used as a
Local Oscillator
A Class-S Emergency Position-Indicating Radio Beacon (E.P.I.R.B)
- Must be capable of floating or being secured to survival.
- Must have its battery replaced after emergency use.
- May be tested during the first five minutes of any hour
A PPI cathode-ray tube as used on a radar set
indicates both the range and azimuth of a target
the resonant frequency of a cavity resonator depends upon
Physical Dimensions
The maximum usable range of the usual radar set (on any particular range setting) is determined by
The interval between transmitted pulses
A reflex klystron is oscillating at the frequency of its resonant cavity. If the reflector voltage is made slightly less negative, the
The frequency will decrease
In a pulsed radar set, the STC circuit is used to
Reduce interference from the effects of sea return
The coarse frequency adjustment of a reflex klystron is accomplished by
Adjusting the flexible wall of the resonant cavity
In a pulsed radar set, the function of the duplexer is to
Allow the transmitter and the receiver to operate from a common antenna
A magnetron is operated at a duty cycle of 0.001. It has a peak power output of 100 kilowatts. Its average power is
100 watts
The aquadag coating on the inside of PPI tube is used
As a second anode and to prevent the build-up of secondary field
If the duration of the radar transmitted pulse, on a particular range of operation, is increased, the required bandwidth of the receiver’s IF amplifiers
May be decreased
The main frequency-determining element of a klystron is
Its resonant cavity
A thin layer of dirt and grime covers the reflecting surface of the parabolic dish of a radar set. The particular effect on the performance of the radar will be
No noticeable effect
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?
Isolator
It is possible to increase the maximum range of radar equipment by
- Lowering the pulse frequency
- Raising the peak power of the transmitter 3. Narrowing the beam width and increasing the pulse duration
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
The shortest possible time
Which of the following is used as a high-power microwave oscillator?
Magnetron
Which of the following operating frequencies is used for the modern loran navigational system?
Loran C: 100 kHz
Which ferrite device can be used instead of a duplexer to isolate a microwave transmitter and receiver when both are connected to the same antenna?
Circulator
The pulse frequency is equal to
Duty Cycle
In a radar set, a blocking oscillator can be used to
Produce a trigger pulse for the transmitter
The intensity of the echoes (target definition) on a PPI display is determined by
Pulse frequency and antenna rotation rate
A duplexer circuit allows a transmitter and a receiver to operate from the same antenna with virtually no interaction. This circuit may be replaced by a
Circulator
The repetition rate of a pulsed radar system indicates the
Frequencies of the duty cycle
The radar set, the sensitivity-time control circuit
Can reduce sea-return response
Which of the following is the ferrite device that buffers a microwave source from the effects of a varying load, and thereby prevents the formation of standing waves?
Isolator
Pulsed radar sets are primarily used to find the
Target’s range and bearing
Which of the following factors is mainly concerned in the design of an antenna system for a pulsed radar set?
Radio frequency
The main benefit of using microwaves is
More spectrum space for signals
Radio communication are regulated in the Philippines by the
NTC
Which of the following is not a disadvantage of microwaves?
Higher-cost equipment
Which of the following is a microwave frequency?
above 3 GHZ
Which of the following is not a common microwave application?
Mobile Radio
Coaxial cable is not widely used for long microwave transmission lines because of its
High loss
tripline and microstrip transmission lines are usually made with
PCBs
The most common cross-section of a waveguide is a
Rectangle
A magnetic field is introduced into the waveguide by a
Probe
When the electric field in a waveguide is perpendicular to the direction of wave propagation, the mode is said to be
TM
Signal propagation in a waveguide is by
Electric and Magnetic Fields
Decreasing the volume of a cavity causes its resonant frequency to
Decrease
__________ is a popular microwave mixer diode
Hot Carrrier
Varactor and step-recovery diodes are widely used in what type of circuit?
Frequency Multiplier
Which diode is a popular microwave oscillator?
Gunn diode
A reflex klystron is used as
Oscillator
For proper operation, a magnetron must be accompanied by a
permanent magnet
The operating frequency of klystrons and magnetrons is set by the
cavity resonators
A magnetron is used only as a/an
oscillator
A common application for magnetron is in
Radar
The most widely used microwave antenna
Horn
is a measure of reliability expressed as the average number of hours between successive failures
MTBF (Mean Time Between Failures)
The free space attenuation between two microwave antennas 40 km apart operating at 8 GHz is
142.55dB
An active microwave radio repeater that can provide drops and inserts
Baseband Repeater
If the correction factor k equals 4/3 of the earth’s curvature, the microwave beam would have a curvature that is ___________ than that of the earth
More
The optimum clearance from an obstacle in a microwave system is accepted as __________ of the first fresnel zone radius.
0.6
The microwave beam curves the same as that of the earth when the value of the correction factor k equals
Infinity
The ability of a radar to determine the bearing of a target depends upon the
Antenna directivity
The Doppler effect allows which characteristics of a target to be measured.
Speed
The Doppler effect is a change in what signal characteristics are produced by relative motion between the radar set and a target.
Frequency
The most widely used radar transmitter component is a
Magnetron
