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

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

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

Answer 5

E field

Question 6

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

a) audio
b) mean carrier
c) envelope depth

Answer 6

Mean carrier

Question 7

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 7

During the night time

Question 8

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 8

The same as the highest modulating frequency

Question 9

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 9

Groundwave propagation only

Question 10

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 10

8850 kHz

Question 11

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 11

1st Intermediate Frequency (IF) as high as possible

Question 12

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 12

Frequency and phase comparator

Question 13

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 13

Quarter wavelength from the short circuit

Question 14

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 14

3.2 watts

Question 15

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 15

60 dB

Question 16

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 16

The rate of deviation is increased

Question 17

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 17

119.997 MHz, 120.000 MHz, 120.003 MHz

Question 18

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 18

Power saving, bandwidth reduction

Question 19

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 19

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

Question 20

Absorption by the ionosphere is greatest:

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

Answer 20

During the day

Question 21

Buffer amp on transmitter is between:

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

Answer 21

Local oscillator and modulator

Question 22

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 22

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

Question 23

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 23

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

Question 24

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 24

USB or LSB only is transmitted

Question 25

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

a) HF
b) VHF
c) SATCOM

Answer 25

VHF

Question 26

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 26

3 MHz to 30 MHz

Question 27

Over-modulation will:

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

Answer 27

Produce massive distortion

Question 28

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

Answer 28

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

Question 29

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 29

An input balanced about earth potential

Question 30

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 30

Stay the same