Avionics MCQs – Ground Stations
1 - Question
What is the use of the band pass filter in the receiver section?
a) Protects the receiver
b) Increases antenna gain
c) Reduces noise
d) To reduce it to an intermediate frequency
Explanation: The diplexer feeds a bandpass filter (BPF) in the receiver section that ensures that only the received frequencies pass through to the sensitive receiving circuits. This bandpass filter blocks the high-power transmit a signal that can occur simultaneously with reception. This prevents overload and damage to the receiver.
2 - Question
The satellite in the earth station must be steerable even for a geosynchronous satellite.
Explanation: It must be possible to adjust its azimuth and elevation so that the antenna can be properly aligned with the satellite. Earth stations supporting geosynchronous satellites can generally be fixed in position, however, azimuth and elevation adjustments are necessary to initially pinpoint the satellite and to permit minor adjustments over the satellite’s life.
3 - Question
In Rf tuning, what is the first local oscillator?
a) Quartz oscillator
b) Frequency synthesizer
c) Magnetic oscillator
d) Electric oscillators
Explanation: In RF tuning, the first local oscillator is made adjustable. Generally, a frequency synthesizer is used in this application. The frequency synthesizer generates a highly stable signal at selected frequency increments.
4 - Question
If the earth station downlink signal received is at fs = 4.08 GHz, what first stage local-oscillator frequency fLO is needed to achieve IF of 770 MHz?
a) 3310 MHz
b) 4080 MHz
c) 1203 MHz
d) 3250 MHz
Explanation: fIF = fs – fLO fLO = fs – fIF = 4080 – 770 = 3310 MHz.
5 - Question
Which of the following amplifiers is used in the transmitter substation?
a) RF amplifiers
b) Buffer amplifiers
c) Klystron amplifier
d) Operational amplifiers
Explanation: The signals to be sent to the satellite might be TV programs, multiple telephone calls, or digital data from a computer. These signals are used to modulate the carrier, which is then amplified by a large traveling-wave tube or klystron amplifier.
6 - Question
Which part of the transmitter subsystem modulates the baseband signal?
b) Up converter
c) Power amplifiers
Explanation: The transmit subsystem consists of two basic parts, the up converters and the power amplifiers. The up converters translate the baseband signals modulated on to carriers up to the final uplink microwave frequencies.
7 - Question
In digital systems, analog signals are first digitized with PCM converters before modulation.
Explanation: In digital systems, analog signals are first digitized with PCM converters. The resulting serial digital output is then used to modulate a QPSK modulator.
8 - Question
In RF tuning, _________ provides the final up conversion to the microwave frequency?
a) Fixed-frequency local oscillator
b) RF frequency synthesizer
c) Quartz oscillator
d) Magnetic oscillator
Explanation: In RF tuning, a mixer fed by a fixed-frequency local oscillator performs an initial up conversion to 700 MHz. Then a sophisticated RF frequency synthesizer applied to a second mixer provides up conversion to the final microwave frequency.
9 - Question
When individual up converters are used to modulate a channel, what is used to combine them into final signal?
a) Microwave combiner
Explanation: Individual up converters are used on each modulated channel. At the output of the up converters, all the signals are combined in a microwave combiner, which produces a single output signal that is fed to the final amplifiers.