Radio principles Flashcards
Speed of sound sea level, 20,000 ft and 40,000 ft
Sea level = 660 kts
20,000 = 610 kts
40,000 = 570 kts
Human ear frequencies
20-20,000hz
Radio waves
Variation in strength of electric and magnetic fields.
Does not require medium.
Travel greater distance than sound.
Travel at speed of light (300,000km per second).H
HF band
High frequency
3 MHZ to 30 MHZ
Commonly used for long distance communications
VHF band
30 MHZ to 300 MHZ.
Preffered means of communication in aviation
Why is VHF preffered
Large number of frequencies.
VHF frequencies less prone to interference
Why VHF line of site
Can not bend around obstacles
Why can HF frequencies bend
The variations in density of free electrons in the ionosphere cause HF radio waves to refract (bend), allowing the upper atmosphere to be used as a reflector for communications between distant locations on the ground.
AM modulation
Amplitude modulation
Superimposing of intelligence on the carrier wave by varying the amplitude of the waves while the frequency remains constant. e.g. cardiograph
FM modulation
Frequency modulation.
Superimposing intelligence upon the carrier wave by varying the frequency of the waves while amplitude remains constant.
Clearer signals and greater availability of channels within given frequency range than am
Two types of microphones
Dynamic and electret
Electret is smallest and lightest, act on voice, ignore environmental sounds,
Radio on procedure
Check avionics power switch on.
Check microphone and associated leads are plugged correctly.
Switch radio on.
Select desired frequency.
if audio panel fitted, select appropriate radio switch to speaker/phones.
Adjust volume and squelch to desired level.
Radio not working procedure
Check master switch/avionics switch.
Check radio on/off switch, and NAV/COM set COM side is on.
Correct audio panel settings.
Check circuit breakers/fuses.
Check all connections (microphone/headphone plugs, correct socket).
Check correct frequency (COM not NAV).
Check volume and squelch (not fully anticlockwise)
Transponder principle of opperation
Signal sent from sound based radar unit. Received by transponder. Transponder sends back coded signal to radar. Bearing and distance from ground radar (or ACAS) can be determined
What mode information is transponder 4 figure code
Mode A - transmitted back to ground radar (or ACAS) upon each interrogation from originating unit