EMS 3

Question 1

Explain the relationship between wavelength and frequency

Answer 1

Wavelength is inversely proportional to frequency.
As wavelength increases, frequency decreases
As wavelength decreases, frequency increases

Question 2

Describe the unit of measure for frequency

Answer 2

The unit of measure for frequency is Hertz (Hz) which
indicates cycles per second.

Question 3

Describe Reflection

Answer 3

Reflection happens when a wave hits a smooth object that is larger than the wave itself, depending on the object the wave may bounce in another direction.

Question 4

Describe Refraction

Answer 4

Refraction, which is the bending of an RF signal, occurs as the signal passes through an object that is a different density, causing the direction of the wave to change.
RF refraction most commonly occurs as a result of atmospheric conditions.
The tree most common causes of refraction are: Water Vapour, Changes in the air temperature, Changes in air pressure.

Question 5

Describe Scattering

Answer 5

Electromagnetic Radiation is attenuated, weakened, by its passsage through the atmosphere via scattering and absorption.
Scattering occurs when a signals wavelength is larger than the medium it encounters and either relects from or passes through.
Scattering differs from reflection as the firection associated with scattering is unpredictable, where as the direction of reflectino is predictable based on the angle the signal strikes the obstruction.

Question 6

Describe Diffraction

Answer 6

Diffraction is the bending and spreading of an RF signal around an object.
Diffraction does not occur with every signal that encounters an object, and depends entirely on the shape, size and material of the obstructing object, as well as the characteristics of the RF signal such as polarisation, phase and amplitude.
Typically, diffraction occurs when there is a partial blackage of the RF signal path such as a hill or building.

Question 7

Describe Line of Sight

Answer 7

Line of Sight radio wave propagatin, often abbreviated to LOS, is the term used for radio waves travelling in a straight line from the transmitting antenna to the receiving antenna.
This translates to that if ther are any obstructions, such as a hill, mountain or builidn gbetween either antenna the signal will not be received.

Question 8

Describe the properties associated with the transmitted wave

Answer 8

1. The wave is transverse.
2. The wave requires no supporting
   medium.
3. The wave travels in straight lines.
4. The orientation of the Electric field
   determines polarisation.
5. The transmitted wave can be
   reflected, refracted or experience
   a Doppler Shift.
6. As the wave propagates it is
   attenuated in the atmosphere.

Question 9

Describe Surface Waves

Answer 9

A surface wave transmission path follows the contours of
the earth
* Surface waves are not greatly affected by terrain or
obstacles
* Dominant below HF (3MHz)
* No atmospheric interaction so a very reliable mode

Question 10

Describe Sky Waves

Answer 10

A sky wave transmission path involves the EM wave
being bent (refracted) back to the Earth’s surface by the
ionosphere

Question 11

Describe Space Waves

Answer 11

A space wave transmission path involves
propagation in a straight line between the
transmitter and receiver. (Line of Sight)
* Space wave transmission paths suffer from
multi-pathing due to ground reflection
* Dominant in VHF and above (30MHz)

Question 12

Describe the effect of the ionosphere on electromagnetic propagation.

Answer 12

A region of the earth’s atmosphere where ionisation caused by incoming solar radiation affects the transmission of radio waves.
Dependent on radio wave frequency, ionisation of the ionosphere causes radio waves to be attenuated, reflected and refracted.

Question 13

Describe Attenuation

Answer 13

Attenuation is a loss of power in the transmitted wave.
* Attenuation occurs due to absorption and
spreading loss.
* Electromagnetic energy is absorbed by oxygen and water vapour, then dissipated as heat. The wave is attenuated during propagation from the transmitter to the receiver.

Question 14

Describe Spreading Loss

Answer 14

As the transmitted wave propagates further from the transmitter it must cover more area. Therefore the wave will decrease in strength.
This reduction in strength is termed spreading loss.
* Double the distance = ¼
power

Question 15

Describe the Ionosphere, and the effects of the Ionosphere

Answer 15

A region of the earth’s atmosphere where ionisation caused by incoming solar radiation affects the transmission of radio waves.
Dependent on radio wave frequency, ionisation of the ionosphere causes radio waves to be attenuated, reflected and refracted.