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
Why is care exercised in the allocation of VHF frequencies to stations within reception range of each other
If stations are on the same VHF frequency, loss of signal would result if a number of aircraft transmit at the same time
What is a transceiver
A radio set is both a transmitter and a receiver
What is a NAV/COM set
VHF navigation receiver and the communication transceiver in one radio set
What is an audio selector panel
Connects the various NAV and COM radio sets to the speaker or headphones, and the COM sets (if more than one) to the microphone.
Types of microphones
hand-held microphone and the boom-mike
Advantages of the boom mike
It allows you to operate your radio without having to take your hands off the control column
How does the microphone work
Converting pressure waves produced by your voice into electromagnetic signals through the use of vibrating carbon particles or a diaphragm in the microphone
What is intelligence
Your spoken words
is it possible to transmit your messages directly as radio waves
No
What is the carrier wave
The radio frequency signal sent out when you press the microphone button (without speaking into it)
Modulation
The superimposing of intelligence on a radio carrier wave
Two types of modulation
Amplitude Modulation (AM) and Frequency Modulation (FM)
What is AM
Involves the superimposing of intelligence upon the carrier wave by varying the amplitude of the waves while the frequency (and thus wavelength) remains constant.
What is FM
Involves the superimposing of intelligence upon the carrier wave by varying the frequency of the waves while the amplitude remains constant.
Why is FM better then AM
Production of clearer signals and a greater availability of channels within a given range of frequencies
What happens if the microphone is positioned too far away from your mouth
The pressure waves on the diaphragm will be weaker and the electromagnetic signals will be weaker
What happens if you speak too loudly into the microphone
The strong pressure waves will cause the diaphragm to vibrate to their full travel and distorted signals are the likely result
What must you do before speaking into the microphone
Hold down control column button
is it possible to receive messages whilst you are transmitting
No
When transmitting your message on a given frequency is it possible for other transmissions on that frequency within range
No
Why is it important to release the microphone button
You are blocking the frequency and no other stations can use it with clarity
What is a squelch
Eliminates unwanted signals such as static
What do you do when the volume control is set to a desired level and static is being experienced
Turn squelch down until unwanted noise ceases
What happens if you turn the squelch fully down
Cut out the signal as well as the static
What must you do before transmitting through the mic
- Listen out on the frequency to be used. Only commence transmitting when the frequency is clear and your transmission is not likely to block or interfere with users already on the frequency.
- Decide on what you want to say
Fault finding procedure for radio not working
- Master, avionics, radio ON
- Correct settings on the audio selector panel
- Check circuit breaker
- Mic leads
- Correct frequency
- Volume + Squelch level
What radio equipment can not be used for transmissions
ELT and Transponder
Transponder purpose
Enables a ground-based radar controller to determine the location (and altitude in most cases) of an aircraft. The information can also be obtained by the pilot of an aircraft equipped with an ACAS in order to ascertain the position of other transponder equipped aircraft in its vicinity
ACAS
Airborne Collision Avoidance System
How does a transponder work
A signal sent from a ground-based radar unit is received by the aircraft transponder. The signal triggers the aircraft transponder to send a coded signal back to the radar unit. Bearing and distance information from the ground radar unit (or ACAS equipped aircraft) can thereby be determined.
Request to operate without a transponder transmission
The pilot must append the words “NEGATIVE TRANSPONDER” to the request.
How is transponder mandatory airspace indentified
The letters TM on visual aeronautical charts
What airspace in NZ is TM
Controlled
Transponder mode a info
Four figure code
Transponder mode c info
Altitude
Transponder functions
- OFF
- SBY
- ON
- ALT
- TST
Transponder OFF
Transponder is off
Transponder SBY
The transponder is switched on but will not reply to (radar) interrogation
Transponder ON
Send mode a info only
Transponder ALT
Send mode a and c info
Transponder TST
Transponder test function
Transponder code 1200
Fixed wing aircraft flying VFR
Transponder code 1500
Helicopter flying VFR
Transponder code 2200
Aircraft operating in the circuit of a controlled aerodrome
Transponder 7500
Unlawful interference (hijacking)
Transponder code 7600
Communications failure
Transponder code 7700
Emergency
Squawk indent
Press transponder INDENT button once. This causes your aircraft symbol on the radar screen to flash so that the controller can readily identify your aircraft. You must not push the IDENT button unless instructed.
HF radios
Transmissions are reflected back to earth by the ionosphere (a layer of charged ions in the stratosphere). These reflected signals (sky waves) are able to reach much further than VHF transmissions and in the case of mountainous terrain shielding VHF signals the HF reflected transmissions can reach aircraft flying in the lee of mountains
Disadvantages of HF
Static interference and signal fading
Radio aerial length
The length of an aerial is related to the wavelength (and therefore frequency) of the signals. As a rule, an aerial should be equal in length to the wavelength of the signal or half the wavelength or quarter wavelength
HF and VHF aerial length
VHF, being of very high frequency and short wavelength, requires a shorter aerial than HF which has a longer wavelength
