Ch. 1 - Radio Principles Flashcards
Do sound waves require a medium to be effective
Yes
Do radio waves require a medium to be effective
No
What speed do sound waves travel at
Speed of sound
relationship between speed of sound and altitude
Speed of sound decreases with altitude
Speed of sound at sea level
660kt (340m/s)
Speed of sound at 20,000ft
610kt
Speed of sound at 40,000ft
570kt
Why does the speed of sound decrease with altitude
The speed of sound is dependent on air temperature and temperature decreases as altitude increases
What frequencies can the human ear respond to
20-20,000Hz
What are audio frequencies
All frequencies that the human ear can respond to
How many cps in 1,000,000Hz
1,000,000cps
How many Hz in 1MHz
1,000,000Hz
What happens to air when sound waves pass through it
Compression and expansion of air pressure in a regular and symmetrical manner, because waves move through the air, the air doesn’t move
What type of waves are radio waves
Electromagnetic waves
Do radio waves require a medium
No
What happens to radio waves when the pass-through dense mediums such as brick
They attenuate at rate dependent on the density of the medium and the frequency of the wave
Do sound or radio waves travel further
Radio
Which is slower radio or sound waves
Sound
What speed to radio waves travel at
Speed of light
What is the speed of light
300,000km/s
What property of radio waves is key to radiotelephony
The ability to select one particular frequency, because if a message was to be sent using sound waves the recipient would receive all the frequencies associated with the transmitted pressure pattern but being able to use radio waves on a selected frequency means that all other frequencies are filtered out and a clear signal is a result, an added advantage of this is that specific frequencies can be selected for specific purposes.
What is the purpose of the microphone
Transfer your spoken words into electromagnetic radio waves, which can be sent to a receiver
Wavelength
The length of a single wave (or of one complete cycle). It is also the distance travelled by the wave during transmission of one cycle
Frequency
The number of completed waves passing a point in one second
Frequency increase = wavelength ______
Decreases
Amplitude
The distance from the top or bottom of the wave to the mean value line of a wave
Greater amplitude = Greater ______
Volume/strength of a signal
Types of frequency bands
HF (high frequency), VHF (very high frequency)
VHF range
30MHz - 300Mhz
HF range
3MHz - 30MHz
Advantages of VHF
Lots of frequencies can support the high number of services required and the reception is better than those at lower frequencies which are prone to interference
Disadvantage of VHF
Inability of signals to ‘bend’ around obstacles such as mountains.
Relay equipment in NZ
The mountainous terrain in New Zealand reduces VHF range considerably in some areas and for that reason automatic relay equipment has been installed on high ground, which continues to provide access to high quality communications on VHF (line-of-sight) frequencies over most of the country.
Why does VHF range increase with alt
The higher you fly, the further you see