13.4 Radio and Radar - Fundamentals - Example Questions

Question 1

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

Answer 1

May be higher than the CF, dependent upon the angle of incidence

Question 2

If a director is removed from an aerial array, then:

a) beam width increases
b) aerial gain increases
c) side lobes decrease

Answer 2

Beam width increases

Question 3

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

Answer 3

Degree of mismatch

Question 4

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

Answer 4

Approximately eqeual to 2/3 velocity of propagation of free space

Question 5

The purpose of a limiter in a transmitter is to give:

a) optimum modulation
b) a higher mean modulation depth
c) more modulation of vowels

Answer 5

A higher mean modulation depth

Question 6

Polarisation of a High Frequency (HF) radio wave is the same as the:

a) E field
b) H field
c) direction of propagation

Answer 6

E field

Question 7

What part of the signal causes Automatic Gain Control (AGC) output in a Comms receiver:

a) audio
b) mean carrier
c) envelope depth

Answer 7

Mean carrier

Question 8

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

Answer 8

During the night time

Question 9

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

Answer 9

The same as the highest modulating frequency

Question 10

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

Answer 10

Groundwave propagation only

Question 11

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

Answer 11

8850 kHz

Question 12

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

Answer 12

1st Intermediate Frequency (IF) as high as possible

Question 13

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

Answer 13

Frequency and phase comparator

Question 14

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

Answer 14

Quarter wavelength from the short circuit

Question 15

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

Answer 15

3.2 watts

Question 16

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

Answer 16

60 dB

Question 17

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

Answer 17

The rate of deviation is increased

Question 18

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

Answer 18

119.997 MHz, 120.000 MHz, 120.003 MHz

Question 19

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

Answer 19

Power saving, bandwidth reduction

Question 20

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

Answer 20

Ensure the background noise is not heard in the phones with no signal or very weak signals

Question 21

Absorption by the ionosphere is greatest:

a) during the night
b) at sunrise and sunset
c) during the day

Answer 21

During the day

Question 22

Buffer amp on transmitter is between:

a) modulator and power amp
b) local oscillator and modulator
c) local oscillator and demodulator

Answer 22

Local oscillator and modulator

Question 23

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

Answer 23

At right angles to one another, with both of these at right angles to the direction of propagation

Question 24

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

Answer 24

This is the function of a microphone that converts acoustical energy into electrical energy

Question 25

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

Answer 25

USB or LSB only is transmitted

Question 26

Which of the following mediums is used for short range communications:

a) HF
b) VHF
c) SATCOM

Answer 26

VHF

Question 27

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

Answer 27

3 MHz to 30 MHz

Question 28

Over-modulation will:

a) produce a loud output signal
b) produce maximum feedback
c) produce massive distortion

Answer 28

Produce massive distortion

Question 29

One short coming 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

Answer 29

The inability to cover polar areas. The limit of cover is 81.5° north and south at sea level

Question 30

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

Answer 30

An input balanced about earth potential

Question 31

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

Answer 31

Stay the same