Module 5

Question 1

How far above the earth is the Ionosphere
What signals are refracted by it

Answer 1

70-400km above the earth
VHF and UHF pass through, HF signals are refracted back to Earth

Question 2

When can you send HF signals around the world

Answer 2

HF bands are ‘open’ (support Skywave propagation) at different times of the day and the year

Each band affected differently

Solar activity has a big effect

Question 3

Range of VHF/UHF vs HF

What factors can affect it

Answer 3

Limited to just beyond line-of-sight
Less than HF
Range decreases as frequency increases

Gets weaker when penetrating buildings, glass not as bad
Snow, ice and heavy rain can attenuate signals at UHF and above
Hills can cause radio “shadows”

Question 4

What is the range of VHF/UHF dependant on

What is better: higher up or more power

Answer 4

Antenna height
Antenna gain (using a beam antenna)
A clear path
Transmitter power

Higher up as it improves both transmit and receive performance

Question 5

What atmospheric conditions can extend the range of VHF/UHF

Answer 5

They pass through Ionosphere but propagation can occur through the Troposphere (below Ionosphere)

Sporadic E and Atmospheric ducting, no clue