Radio Transmissions Flashcards
How are wavelengths modulated?
Frequency and Amplitude modulated to carry information across a carrier wave.
What does the first letter in an emission class represent?
A - Double Sideband
H - Single sideband full carrier
J - Single sideband suppressed carrier
R - Single sideband reduced carrier
F - Frequency modulation
G - Phase modulation
What does the number in an emission class represent?
1 - Single channel containing quantized or digital information without the use of a modulating sub-carrier.
2 - Single channel digital information with the use of a modulating sub-carrier
3 - Single channel containing analogue information.
8 - More than one channel containing analogue information.
What does the second letter in an emission class represent?
B- Telegraphy for Automatic response
E - Telephony
What is the Ionosphere and how does it affect radio waves?
The Ionosphere is a section of the troposphere full of charged ions that can deflect and absorb radio waves.
What are the layers of the Ionosphere?
D, E, F1 and F2.
How do the affects of the ionosphere change?
Constantly changing in relation to volume of solar energy with higher frequency waves being less affected.
What are Sky waves?
Radio waves transmitted skywards that are reflected by the ionosphere. Propagation determined by frequency and time of day.
What are Ground Waves?
Radio waves that transmit following the shape of the ground. Max range of 250nm
What are Space Waves?
Radio waves that travel by line of sight. Max range of 50nm.
What are Escape Waves?
Radio waves of higher enough frequency to pass through the ionosphere. Used for satellite communications.
What is Skip Distance?
The distance across ground which a sky wave travels to from point of transmission, reflection to reception.
What is Skip Zone?
The area between the end of the ground wave range and the end of the skip distance where neither transmission is recieved.
What is Fading?
A phenomenon that occurs when the ground and sky wave propagation distance are the same and the signals come in out of phase. This weakens of cancels out the transmission.
What is Ducting?
A phenomenon that occurs when a warm dry layer of air sits between two cold moist layers the radio waves can be reflected multiple times between the layers. This can double or even quadruple the range of the transmission.
