WorksheetsEST 27
Total questions: 50
Worksheet time: 25mins
__________ is the progressive decrease of signal strength with increasing distance.
Radiation
Attenuation
Modulation
Propagation
Calculate the effective earth’s radius if the surface refractivity is 301.
8493 km
8493 mmi
6370 km
6370 mi
If k-factor is greater than 1, the array beam is bent
Away from the earth
towards the ionosphere,
towards the earth
towards the outer space
The antenna separations (in meters) required for optimum operation of a space diversity system can be calculated from:
where R = effective earth radius (m) and L = path length (m)
S = 2λR/L
S = 3λR/L
S = λR/RL
S = λR/L
Rainfall is an important factor for fading of radio waves at frequencies above
10 GHz
100 GHz
1 GHz
100 MHz
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.
Third
Fourth
Fifth
Sixth
What do you call an attenuation that occurs over many different wavelengths of the carrier?
Rayleigh fading
Rician fading
Wavelength fading
Slow fading
Which of the reception problems below that is not due to multipath?
Delayed spreading
Rayleigh fading
Random Doppler shift
Slow fading
Which causes multipath or frequency-selective fading?
Small reflector
Nearer reflector
Further reflector
Large reflector
In microwave transmission using digital radio, what causes most intersymbol interference?
Delayed spreading
Rayleigh fading
Random Doppler shift
Slow fading
A shipboard equipment which measures the distance between the ship’s bottom and the ocean floor.
Fathometer
Echosounder
LORAN
SONAR
The cavity resonator
Is equivalent to an LC resonant circuit
In a reflect klystron has its output taken from the reflector plate
Produces a frequency which is independent of the cavity size.
Has a low Q factor for narrow operation.
At what position is the input signal inserted into a traveling-wave tube?
At the cathode end of the helix
At the collector
At the collector end of the helix
At the control grid of the electron gun
Coupling into and out of a traveling-wave tube can be accompanied by a
Waveguide match
Cavity match
Direct coax-helix match
All of the above
a high-power microwave pulse of the order of megawatts can be generated by a
traveling-wave tube
magnetron
reflex klystron
Gunn diode
A traveling-wave tube (TWT) amplifies by virtue of
The absorption of energy by the signal from an electron stream
The effect of an external magnetic field
The energy contained the cavity resonators
The energy liberated form the collector
What is the purpose of the electromagnetic field which surrounds a traveling-wave tube?
To accelerate the electron
To velocity modulate the electron beam
To keep the electrons from spreading out
To slow down the signal on the helix
Which of the following is used as an oscillator device in the SHF band?
Thyratron tube
Tunnel diode
Klystron tube
Both B and C
Microwave frequencies are normally regarded as those in the range of
1 to 500 MHz
1000 to 10,000 GHz
1 to 100 GHz
10 to 1000 GHz
The highest frequency which a conventional vacuum-tube oscillator can generate is not limited by the
Electron transit time
Distributed lead inductance
Inter-electrode capacitance
Degree of emission from the cathode
As the electron beam moves through a klystron’s intercavity drift space
Frequency modulation at the input cavity creates velocity modulation at the output cavity
Velocity modulation at the input cavity creates density modulation at the output cavity
Density modulation at the input cavity creates velocity modulation at the output cavity
Phase modulation at the input cavity creates velocity modulation at the output cavity.
The frequency of the oscillation generated by a magnetron, is mainly determined by
The flux density of the external magnet
The ratio of the dc cathode voltage to the magnetic flux density
The number of the cavity resonators
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 the
π mode
π/2 mode
2π mode
π/4 mode
The Gunn diode oscillator
Is capable of generating continuous microwave power of the order of kilowatt
Generates frequencies which are below 100 MHz
Operates over a positive resistance characteristic
Depends on the formation of charge domain
What ferrite device can be used instead of duplexer of isolate microwave transmitter and receiver when both are connected to the same antenna?
Isolator
Magnetron
Simplex
Circulator
To achieve good bearing resolution when using a pulsed-radar set, an important requirement is
A narrow, antenna-beam width in the vertical plane
A narrow, antenna-beam width in the horizontal plane
A low repetition rate
A high duty cycle
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 synchronizer
Which may be used to tune the radar receiver
To the tone of the pulse repetition
Tune the magnetron to the correct frequency
In a radar-set receiver, the usual mixer stage is
And FET
A tunnel diode
A silicon crystal
A Rochelle salts crystal
Klystron oscillators are most often used in the frequency range of
300 to 3000 MHz
3000 to 30000 MHz
30 to 30000 MHz
10 to 10000 MHz
Oscillators of a klystron tube are maintained
By bunches of electrons passing the cavity grids
By plate-to-cathode feedback
By feedback between the accelerating grid and the repeller
By circulating bunches of electrons within the cavities.
What allow microwave to pass in only one direction?
RF emitter
Capacitor
Varactor-triac
Ferrite emitter
In an SHF pulsed radar set, a reflex klystron can be used as a
Single mixer stage
Local oscillator
Transmitter oscillator
Duplexer stage
A Class-S Emergency Position-Indicating Radio Beacon (E.P.I.R.B)
Must be capable of floating or being secured to a survival
Must have its battery replaced after emergency use
May be tested during the first five minutes of any hour
All of these
A PPI cathode-ray tube as used on a radar set
Is used to check the percentage of modulation
Indicates both the range and azimuth of a target
Indicates only the range of a target
Is used for receiver alignment
The resonant frequency of a cavity resonator depends upon
The mode of operation
Its electrical dimensions
Its physical dimensions
The capacitor which tunes it
The maximum usable range of the usual radar set (on any particular range setting) is determined by
The width of the transmitted pulses
The interval between transmitted pulses
The bandwidth of the receiver IF stages
The duty cycle
A reflex klystron is oscillating at the frequency of its resonant cavity. If the reflector voltage is made slightly less negative, the
Oscillation will cease
Output power would increase
The frequency will decrease
Bunching would occur earlier in time
The coarse frequency adjustment of a reflex klystron is accomplished by
The AFC system
Adjusting the flexible wall of the resonant cavity
An adjustment in the synchronizer
Varying the repeller voltage
In a pulsed radar set, the STC circuit is used to
Improve the target bearing resolution
Increases receiver sensitivity for echoes from targets
Vary the pulse frequency in order to control the maximum target
Reduce interference from the effects of sea return
In a pulsed radar set, the function of the duplexer is to
Aid in calibrating the display unit
Prevent frequency drift in the klystron
Allow the transmitter and the receiver to operate from a common antenna
All of these
A magnetron is operated at a duty cycle of 0.001. It has a peak power output of 100 kilowatts. Its average power is
10,000 watts
100 watts
1,000 watts
1,000,000 watts
The aquadag coating on the inside of PPI tube is used
To focus the beam of primary electrons
To shield the electron beam from unidirectional magnetic
As a second anode and to prevent the build-up of secondary field
All of these
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
Must remain as before
Must be increased
May be decreased
Must be doubled
The main frequency determining element of a klystron is
The repeller voltage
The accelerating voltage
Its resonant cavity
Its mode of operation
A thin layer of dirt and grime coverts the reflecting surface of the parabolic dish of a radar set. The particular effect on the performance of the radar will be
A decrease in range
A reduction in horizontal resolution
No noticeable effect
A decrease in gain
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
Wave trap
Tunnel diode
Circulator
It is possible to increase the maximum range of a radar equipment by
Lowering the pulse frequency
Raising the peak power of the transmitter
Narrowing the beam width and increasing the pulse duration
All of these
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 long time constant
Low-pass filters
The shortest possible time
The restricted high-frequency response
Which of the following is used as a high power microwave oscillator?
Thyratron
Magnetron
Klystron
Reflex-klystron
Which of the following operating frequencies is used for the modern loran navigational system?
Loran C: 100 kHz
Loran D: 10.2 kHz
Loran A: 1950 kHz
Loran B: 900 kHz
