13.4 Radio and Radar - Fundamentals - Example Questions Flashcards
Maximum usable frequency (MUF):
a) is the same thing as critical frequency (CF)
b) will be lower than the CF at night
c) may be higher than the CF, dependent upon the angle of incidence
May be higher than the CF, dependent upon the angle of incidence
If a director is removed from an aerial array, then:
a) beam width increases
b) aerial gain increases
c) side lobes decrease
Beam width increases
The amount of standing voltage on a line is dependent upon:
a) the length of line
b) characteristic impedance (Z0) of the line
c) degree of mismatch
Degree of mismatch
The velocity of propagation in a transmission line is:
a) equal to the velocity of propagation in free space
b) a constant equal to the speed of light
c) approximately equal to 2/3rd velocity of propagation of free space
Approximately eqeual to 2/3 velocity of propagation of free space
Polarisation of a High Frequency (HF) radio wave is the same as the:
a) E field
b) H field
c) direction of propagation
E field
What part of the signal causes Automatic Gain Control (AGC) output in a Comms receiver:
a) audio
b) mean carrier
c) envelope depth
Mean carrier
Skip Distance’ at High Frequency (HF) is greatest:
a) for the lowest frequencies in the HF band
b) during the night time
c) during the day time
During the night time
The bandwidth of a Single Side Band (SSB) system is approximately:
a) the same as the highest modulating frequency
b) half the highest modulating frequency
c) twice the highest modulating frequency
The same as the highest modulating frequency
Selective fading will not occur in a region of:
a) groundwave propagation only
b) skywave propagation only
c) twice the skip distance from the transmitter
Groundwave propagation only
If a receiver is tuned to 7950 kHz and the local oscillator is tuned to 8400 kHz, the image channel frequency is:
a) 8850 kHz
b) 7500 kHz
c) 7050 kHz
8850 kHz
2nd channel rejection in a double superhet is improved by making the:
a) 1st Intermediate Frequency (IF) as high as possible
b) 2nd IF as high as possible
c) 2nd IF as low as possible
1st Intermediate Frequency (IF) as high as possible
Direct current (DC) tuning voltage in a frequency synthesiser is an output of the:
a) voltage controlled oscillator
b) frequency and phase comparator
c) frequency divider
Frequency and phase comparator
For a short circuit transmission line, an effective parallel tuned circuit will appear:
a) half wavelength from the short circuit
b) one wavelength from the short circuit
c) quarter wavelength from the short circuit
Quarter wavelength from the short circuit
An Amplitude Modulated (AM) transmitter has a carrier output of 20 watts with 80% depth of modulation. The power in each sideband is:
a) 3.2 watts
b) 6.4 watts
c) 16 watts
3.2 watts
An amplifier has an input of 1 millivolt and an output of 1 volt. The gain of the amplifier is:
a) -30 dB
b) 30 dB
c) 60 dB
60 dB
A 100 MHz signal is frequency modulated by a 1 volt 500 Hz sine wave. If the modulating waveform’s frequency is increased to 1 kHz:
a) the rate of deviation is increased
b) the amount of deviation is increased
c) both the rate and amount of deviation is increased
The rate of deviation is increased
The carrier of frequency 120 MHz is AM modulated by a frequency of 3 kHz. The modulated signal will contain frequencies at:
a) 119.9 Hz, 120 MHz, 120.001 MHz
b) 119.997 MHz, 120.000 MHz, 120.003 MHz
c) 119.994 MHz, 120.000 MHz, 120.006 MHz
119.997 MHz, 120.000 MHz, 120.003 MHz
The main advantages of SSB over DSB are:
a) suppression of the carrier, better quality
b) power saving, bandwidth reduction
c) no power output when audio is low, power saving
Power saving, bandwidth reduction
The purpose of squelch is to:
a) ensure the background noise is not heard in the phones with no signal or very weak signals
b) to make provision for weak signals to pass through the receiver
c) enable strong signals to be less amplified
Ensure the background noise is not heard in the phones with no signal or very weak signals
Absorption by the ionosphere is greatest:
a) during the night
b) at sunrise and sunset
c) during the day
During the day
Buffer amp on transmitter is between:
a) modulator and power amp
b) local oscillator and modulator
c) local oscillator and demodulator
Local oscillator and modulator
In Electromagnetic Fields, the radiated energy consists of an Electrical (E) Field, and a Magnetic (H) Field:
a) in line with each other, with both of these at right angles to the direction of propagation
b) at right angles to one another, with both of these at right angles to the direction of propagation
c) at right angles to one another, with both of these in line with the direction of propagation
At right angles to one another, with both of these at right angles to the direction of propagation
How are sound waves converted to alternating current:
a) this is the function of a microphone that converts acoustical energy into electrical energy
b) this is the function of a microwave that converts acoustical energy into electrical energy
c) this is the function of a microphone that converts acoustical energy into sound energy
This is the function of a microphone that converts acoustical energy into electrical energy
In a single sideband system, the:
a) USB or LSB only is transmitted
b) the carrier wave only is transmitted
c) the USB or LSB plus the carrier wave is transmitted
USB or LSB only is transmitted
Which of the following mediums is used for short range communications:
a) HF
b) VHF
c) SATCOM
VHF
What is the frequency band of HF radio?
a) 3 MHz to 30 MHz
b) 118 MHz to 137 MHz
c) 40 MHz to 116 MHz
3 MHz to 30 MHz
Over-modulation will:
a) produce a loud output signal
b) produce maximum feedback
c) produce massive distortion
Produce massive distortion
One shortcoming of geostationary satellites is:
a) its inability to move to areas where the satellite is more necessary
b) the inability to cover polar areas. The limit of cover is 81.5° north and south at sea level
c) the inability to cover equatorial areas
The inability to cover polar areas. The limit of cover is 81.5° north and south at sea level
An electromagnetic microphone input to a VHF comms TX could be:
a) via an energising voltage supply
b) an input balanced about earth potential
c) an input where one input is connected to earth potential
An input balanced about earth potential
If a bandwidth of an aerial is increased by adding a quarter wave stub, the VSWR at the centre frequency will:
a) increase
b) decrease
c) stay the same
Stay the same
