Basic Radio Propagation

Question 1

Which frequencies attenuate more in the atmosphere?

Answer 1

High Frequencies

Question 2

Which frequencies attenuate more in the ionosphere?

Answer 2

Low Frequencies

Question 3

Which frequencies refract more in the ionosphere?

Answer 3

Low frequencies / Long wavelength refract more in the ionosphere

Question 4

What are the two types of ground waves?

Answer 4

Surface waves and space waves

Question 5

Which bands are propagated as surface waves?

Answer 5

VLF, LF, and MF

Question 6

Which bands are propagated as space waves?

Answer 6

VHF +

Question 7

Which bands are propagated as sky waves?

Answer 7

HF

Question 8

Write the radio band frequency spectrum

Answer 8

Question 9

What are the three layers of the ionosphere?

Answer 9

The D, E and F (F1 & F2) Layers

Question 10

Which layers of the ionosphere have the stongest and weakest effect?

Answer 10

The F-layer has the strongest effect and the D-Layer the weakest.

Question 11

What is the other name for the F-layer and at what altitude is it found?

Answer 11

The F-layer is also known as the Appleton layer and is found at approx 225km

Question 12

What is the other name for the E-layer and at what altitude is it found?

Answer 12

The E-layer is also known as the Kennelly-Heaviside layer and is found at approx 125km

Question 13

At what altitude is the D-Layer found?

Answer 13

75km

Question 14

How does the ITU radio regulation classification work?

Answer 14

The first symbol indicates the type of modulation of the main carrier

The second symbol indicates the nature of the signal modulating the main carrier

The third symbol indicates the nature of the information to be transmitted.

Question 15

What happens to the carrier wave when it is modulated?

Answer 15

The resultant radiation consists of the carrier frequency plus additional upper and lower sidebands.

Question 16

Which kind of communication uses a single sideband?

Answer 16

HF VOLMET and HF two-way comms

Question 17

What are the 5 types of modulation?

Answer 17

Keyed, (morse)

AM (altering amplitude)

FM (altering frequency),

Pulse (complex data ie short pulses and larger interruptions - radar)

Phase (phase of carrier reversed - GPS)

Question 18

Define ‘antenna’

Answer 18

A wave-type transducer for the process of converting a line AC into a free electromagnetic wave

Question 19

Define ‘skip distance’

Answer 19

The distance between the transmitter and the point on the surface of the Earth where the first sky return arrives.

Question 20

What is the Skip zone / dead space?

Answer 20

Skip zone/dead space is the distance between the limit of the surface wave and the first returning sky wave

Question 21

What is fading?

Answer 21

When a receiver picks up the sky signal and the surface signal, the signals will interfere with each other causing the signals to be cancelled out.

Question 22

What is the Max Theoretical Range formula?

Answer 22

MTR (nm) = 1.23 × √transmitter height in feet + 1.23 × √receiver height in feet

Question 23

What is the MUF?

Answer 23

The Maximum Usable Frequency (MUF) is the optimum frequency (signal arriving on the reciever) - 100nm

So the frequency is slightly lower than optimum

Question 24

When is reflection more likely?

Answer 24

When the wavelength is simiar to or smaller than the target size

Question 25

Which frequency bands does Super-Refraction (atmospheric ducting) affect?

Answer 25

VHF+

Question 26

What causes Super-Refraction (atmospheric ducting) and what is the effect?

Answer 26

2 Main Causes - A Marked Inversion and a rapid change if humidity with height (Hydrolapse)

Effect - Increases range

Question 27

Which frequency bands does Sub-Refraction affect?

Answer 27

VHF+

Question 28

What causes Sub-refraction and what is the effect?

Answer 28

Caused by water droplets / vapour

Effect - Reduces the range and surface refraction (straightens the signal)

Question 29

Which frequency bands does Sporadic-E affect?

Answer 29

VHF only

Question 30

What causes Sporadic-E and what is it’s effect?

Answer 30

Caused by strong ionisation in the E layer

Effect - Increases range