Basic Radio Propagation Flashcards
Which frequencies attenuate more in the atmosphere?
High Frequencies
Which frequencies attenuate more in the ionosphere?
Low Frequencies
Which frequencies refract more in the ionosphere?
Low frequencies / Long wavelength refract more in the ionosphere
What are the two types of ground waves?
Surface waves and space waves
Which bands are propagated as surface waves?
VLF, LF, and MF
Which bands are propagated as space waves?
VHF +
Which bands are propagated as sky waves?
HF
Write the radio band frequency spectrum
What are the three layers of the ionosphere?
The D, E and F (F1 & F2) Layers
Which layers of the ionosphere have the stongest and weakest effect?
The F-layer has the strongest effect and the D-Layer the weakest.
What is the other name for the F-layer and at what altitude is it found?
The F-layer is also known as the Appleton layer and is found at approx 225km
What is the other name for the E-layer and at what altitude is it found?
The E-layer is also known as the Kennelly-Heaviside layer and is found at approx 125km
At what altitude is the D-Layer found?
75km
How does the ITU radio regulation classification work?
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.
What happens to the carrier wave when it is modulated?
The resultant radiation consists of the carrier frequency plus additional upper and lower sidebands.
Which kind of communication uses a single sideband?
HF VOLMET and HF two-way comms
What are the 5 types of modulation?
Keyed, (morse)
AM (altering amplitude)
FM (altering frequency),
Pulse (complex data ie short pulses and larger interruptions - radar)
Phase (phase of carrier reversed - GPS)
Define ‘antenna’
A wave-type transducer for the process of converting a line AC into a free electromagnetic wave
Define ‘skip distance’
The distance between the transmitter and the point on the surface of the Earth where the first sky return arrives.
What is the Skip zone / dead space?
Skip zone/dead space is the distance between the limit of the surface wave and the first returning sky wave
What is fading?
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.
What is the Max Theoretical Range formula?
MTR (nm) = 1.23 × √transmitter height in feet + 1.23 × √receiver height in feet
What is the MUF?
The Maximum Usable Frequency (MUF) is the optimum frequency (signal arriving on the reciever) - 100nm
So the frequency is slightly lower than optimum
When is reflection more likely?
When the wavelength is simiar to or smaller than the target size
Which frequency bands does Super-Refraction (atmospheric ducting) affect?
VHF+
What causes Super-Refraction (atmospheric ducting) and what is the effect?
2 Main Causes - A Marked Inversion and a rapid change if humidity with height (Hydrolapse)
Effect - Increases range
Which frequency bands does Sub-Refraction affect?
VHF+
What causes Sub-refraction and what is the effect?
Caused by water droplets / vapour
Effect - Reduces the range and surface refraction (straightens the signal)
Which frequency bands does Sporadic-E affect?
VHF only
What causes Sporadic-E and what is it’s effect?
Caused by strong ionisation in the E layer
Effect - Increases range
