COMMS Flashcards
01 What are the Propagation Paths?
Ground Wave
Tropospheric Wave Ducting
Sky Wave
01 What is a ground wave?
Portion of radiated energy which is directly affected by the presence of the earth and its surface features
01 What are the components of ground wave
Surface wave
Space wave
01 What is a surface wave
travels along the surface of the earth and tends to curve over the horizon due to diffraction
Max range in the MF and
low HF bands is ~ 100 NM
01 What is a space wave?
made up of the Direct wave and Earth-reflected wave
VHF bands and higher;
range is line-of-sight
01 What is Tropospheric Wave Ducting
Part of the radiation that undergoes refraction and reflection in the lower levels of the atmosphere.
Provides extra range to LOS comms
Unpredictable
01 What is a sky wave
Waves that travel upward and which are refracted back to earth by the ionosphere.
01 What is a communication system?
A system designed for the purpose of transmitting information from one point to another.
01 A basic communication system is made up of three principle parts:
The transmitter - generates radio frequency power modulates it with the information to be sent;
The receiver - converts the power into a form from which the information can be extracted, and
An antenna system - radiates and intercepts the radio energy.
01 A radio transmitter is composed of two sections:
The radio-frequency section:
generates RF (radio-frequency) waves and
amplifies them so that they have sufficient output power to travel through air or space to the receiver.
The modulator section:
modulates the RF waves with the information that is to be transmitted
01 The radio frequency section of a transmitter consists of:
an oscillator: Generates EM
energy at the desired
frequency. This frequency is called
the CARRIER WAVE
amplifiers: Increases the power of the signal to a level sufficient for transmission
01 The Modulator section of a transmitter consists of:
INFORMATION (INTELLIGENCE): Used to enter the desired info into the transmitter (microphone, keyboard, computer, etc.)
MODULATOR: Impresses the intelligence onto the carrier wave using many different methods
01 The receiver consists of three basic parts:
Selective Circuit: provides selectivity by only allowing energy of a pre‑tuned frequency to pass into the receiver.
This frequency contains both the carrier wave and the intelligence.
Detector: detects and demodulates the intelligence from the carrier wave. (splits the wave in two so we can read the intelligence portion)
Audio Amplifier: (voice radio only) steps up the power and reproduces the intelligence signal for use.
01 What are the receiver characteristics
Frequency coverage
Sensitivity
Selectivity
Fidelity
01 What are the Desirable Receiver Functions
Intercept some of the RF energy from the transmitter.
Select the correct RF from a multitude of signals.
Detect and separate the intelligence from the carrier wave.
Reproduce the intelligence into some meaningful form.
01 What is receiver frequency coverage?
The range of radio frequencies which the receiver can handle.
A single receiver cannot intercept all frequencies.
Receivers are optimized for specific frequency bands.
01 What is receiver sensitivity?
Ability of the receiver to intercept weak signals and extract the intelligence.
A highly sensitive receiver will work for both strong and weak signals.
01 What is receiver selectivity?
Ability of the receiver to intercept and extract intelligence from a desired signal and exclude all others.
01 What is receiver fidelity?
The ability to reproduce the transmitted intelligence.
A high fidelity receiver is not necessarily required for voice comms, but is desirable for such things as a data link.
01 What is the frequency produced by the RF section of a transmitter called?
carrier wave
01 What does the antenna system do?
Couples the radio to free space by radiating RF energy from the transmitter and capturing RF energy by the receiver.
01 What is modulation?
Modulation is the process of varying a carrier signal so that it can convey a message.
02-03 What is a sub-form of AM?
SSB modulation
02-03 What are three advantages of SSB Modulation?
More effective use of avail EM spectrum
Better quality of intercepted signal
Higher % of power used to tx the intelligence
02-03 Why does SSB modulation provide a better quality of sound at the receiver?
Intercepted signal is of better quality.
Better signal-to-noise ratio compared to full sideband modulation.
02-03 What is the main operational disadvantage of FM?
Restricted to LOS due to its use of higher frequencies.
02-03 What are the three digital forms of modulation?
Phase modulation
Pulse modulation
Frequency shift keying
02-03 What are the three forms of modulation?
Amplitude Modulation (AM)
Frequency Modulation (FM)
Digital Modulation
02-03 What is Amplitude modulation (AM)
Modulation method where the amplitude of the carrier wave is increased or decreased in accordance with the changes in the audio signal to be conveyed.
Amplitude modulation produces a signal with power concentrated at the carrier frequency and in two adjacent sidebands.
The transmission bandwidth of an AM signal is more than twice that of the baseband signal.
02-03 What makes up the sidebands?
Sum frequency or upper sideband (USB) = carrier wave frequency + audio frequency
Difference frequency or lower sideband (LSB) = carrier wave frequency – audio frequency
02-03 What is Single Sideband (SSB) Modulation
Form of AM where only one sideband is used to convey information, the rest of the signal is suppressed at the transmission.
No intelligence is conveyed by the carrier wave itself.
Since USB and LSB are mirror images of one another, it is redundant to send both side bands.
02-3 What are the SSB - Advantages
Less power is required for transmission.
-No power is used to transmit the LSB or carrier (carrier wave takes up 2/3 of the antenna power).
-Higher percentage of power can therefore be used to transmit the intelligence.
Only half of the bandwidth is occupied.
-This allows a more effective use of the EM spectrum.
Intercepted signal is of better quality.
-SSB modulation has a better signal-to-noise ratio because it is at least half the size and therefore less susceptible to interference (refer to film).
-SSB modulated signal is also less susceptible to selective fading (when an AM signal strikes the ionosphere, the USB hitting it first will be refracted out of phase with the carrier and LSB.
-This causes distortion when the signal is demodulated at the receiver.
-If only one sideband is used, it can’t be out of phase with itself).
02-03 What is Frequency Modulation (FM)
Modulation method where the frequency of the carrier wave is modified to reflect the changes in the audio signal to be conveyed.
-The loudness or amplitude of the audio signal determines the amount of frequency change to the resting carrier frequency.
-The pitch or frequency of the audio signal determines the rate at which the carrier frequency is affected.
02-03 What is the FM VS AM - Advantages
FM signal-to-noise ratio is better than AM
-Due to its larger size (because amplitude of the signal is varied to convey the information), an AM signal is more susceptible to noise or interference. (Refer to film.)
-If the noise affecting an AM signal is cut, some of the intelligence may be lost as well.
-With FM, limiting the noise does not affect the frequency of the carrier as much and the information can be rendered more clearly.
FM has better fidelity at reception
-To avoid extremely large system components required by high amplitude signals, AM is generally restricted to a narrower bandwidth.
-Because it does not have the large components problem, FM can use a broader bandwidth which allows for all the highs and lows of the original intelligence.
FM allows transmission of signal at constant peak power (because amplitude of the signal does not change).
-Because the signal modulated by frequency does not vary in amplitude, the transmitter tubes may be operated at peak efficiency at all times.
02-03 What is the FM VS AM - Disadvantages
More complex equipment is needed
More bandwidth is used.
-As with AM, sidebands appear above and below the carrier, but the relationship is much more complex and beyond the scope of today’s class.
-Suffice to say that the bandwidth of a commercial FM station is 200 KHz or 20 times that of an AM station.
The main operational disadvantage of FM is that it is restricted to line-of-sight, due to its use of higher frequencies (29.999 MHz and above).
-On VHF and UHF radios, AM is still restricted LOS but HF radios i.e. lower than 30 Mhz provide Beyond Line-of-Sight (BLOS) capability.
02-03 What are the Digital Modulation - Advantages
Send more types of data
Text
Pictures/video
Tactical information
Encryption
Higher fidelity
Better signal to noise ratio
02-03 What are the Digital Modulation - Disadvantages
More complex equipment
More complex transmission protocols
Require Error Correction Codes
02-03 What is phase modulation?
A form of modulation where the phase of the carrier wave is varied by the intelligence signal.
Normally used to transmit digital signals.
02-03 What is pulse modulation?
A form of modulation where the carrier wave is not a continuous alternating wave, but a train of discrete pulses.
Advancements in PM allows for transmission of digital data
02-03 What is Frequency Shift Keying
A form of modulation where a carrier signal of constant amplitude is frequency modulated to correspond to 0 and 1.
02-03 What remains constant during frequency modulation?
Amplitude
02-03 SSB modulation is a sub-form of what kind of modulation?
AM
02-03 Which has the better sound quality, FM or AM?
FM
02-03 What is the main operational disadvantage of FM compared to AM?
Restricted to line of sight
02-03 What does the audio control panel provide aircrew with the means to do?
Communicate internally
Transmit externally
Monitor navigation receivers
Access PA
04 steps to Identifying Objects Outside the Aircraft
Description
Direction (clock system)
High or low indication
Distance
Conflict resolution (“no-conflict” or conflict with instructions)
04 what is the High / Low and Distance
Always indicate if the object is high or low relative to the aircraft unless it is obvious such as a road or runway.
Give an approximate distance if possible.
Calibrate eyeball using available resources.
04 What is the SLIC rule
STOP - If you are talking on ICS, stop!
LISTEN - Listen to the traffic
IDENTIFY - Identify whether or not the traffic is for you directly or relates to your mission.
CONTINUE (or COMMUNICATE and CONTINUE) - Once you are sure that the traffic presents no conflict, you are free to continue.
04 What are the options for Non-Intercom Communications
Runners
Hand signals or gestures
Eye contact
Written notes
05-06 In Winnipeg, and at other large airports, who issues VFR or IFR clearances?
Clearance delivery.
05-06 What are the required standard calls to WOPS at 402?
Start crew
Taxi advisory
Airborne call
Inbound call
Taxiing in call
05-06 When do you call WOPS nd what information do you provide them in air?
Appox. 20 mins back from airport:
Lead will contact WOps and provide the ETA to the ramp, expected fuel on landing, SOB, and the aircraft serviceability.
05- 06 Who do you call for the following clearances?
Flight Plan Clearance
Taxi Clearance
Arrival Clearance
Take-off / Landing Clearance
Flight Plan Clearance (Clearance Delivery)
Taxi Clearance (Ground Control)
Arrival Clearance (Arrival Control)
Take-off / Landing Clearance (Control Tower)
05-06 What is a blind broadcast?
A Blind Broadcast is a VHF call by an aircraft stating its position and intentions to inform other air traffic that may be in the area. They can be either:
Directed (ie. to a specific aircraft or aerodrome).
Non-Directed (broadcast out when in a general area).
When flying VFR in uncontrolled airspace or on an airway, which frequency should be monitored continuously and blind broadcasts sent frequently as a general update of your position?
126.7
05-06 Per the ACSO GB, who will you contct to obtain the latest Metar and TAF?
contact the nearest FIC
ACKNOWLEDGE
> Indicate acknowledgement
ZEV
ACTUAL
> Indicate
actual weather reports
QAM
ALL AFTER
> Indicate
The portion of the message to which I have
reference is all that which follows
AA
ALL BEFORE
> Indicate
The portion of the message to which I have
reference is all that which precedes
AB
BREAK
I hereby indicate the separation between portions of the message.
BT or =
CLOSE WATCH
Indicates closing of watch.
ZKJ
CORRECT
You are correct, or what you have transmitted
is correct.
C
CORRECTION
An error has been made in the transmission.
Transmission will continue with the last word
correctly transmitted.
An error has been made in this transmission
(or message indicated). The correct version is
That which follows is the corrected version in
answer to your request for verification.
C
DISREGARD THIS TRANSMISSION
This transmission is in error. Disregard it. (Shall not be used to cancel a message that has been completely transmitted, and for which receipt or acknowledgement has been received).
EEEEE
DO NOT ANSWER
Stations called are not to answer this call, receipt for this message, or otherwise to transmit in connection with this transmission. Whenever this proword is used the transmission is ended with the proword OUT.
F
EXEMPT
The addressees immediately following are exempted from the collective call.
XMT
EXERCISE
Indicates that message traffic will be of an exercise nature.
FIGURES
Numerals or numbers follow
FLASH
Precedence FLASH
Z
FORECAST
Indicates forecast weather reports
QFZ
FREQUENCY CHANGE
Indicates a change of frequency
QSY
FROM
The originator of this message is indicated by the address designator immediately following.
FM
GROUPS
This message contains the following number of
groups indicated by the numeral following.
GR
IMMEDIATE
Precedence IMMEDIATE
O
INFO
The addresses immediately following are addressed for information.
INFO
INTERROGATIVE
Statement following is a question.
INT
I READ BACK
The following is in response to your instructions
to read back.
G
I SAY AGAIN
I am repeating transmission in its entirety
or portion indicated.
IMI
I SPELL
I will spell the previous word phonetically.
I VERIFY
The following has been verified at your request and is repeated. Use only as a reply to VERIFY.
J
MORE TO FOLLOW
Transmitting station has additional traffic to follow for the receiving station.
B
OUT
This transmission is ended. No response is required or expected.
AR or +
OVER
This transmission is ended. A response is necessary Go ahead; transmit
K
PRIORITY
Precedence PRIORITY
P
READ BACK
Repeat this entire transmission back
to me exactly as received.
G
RECEIPT
Indicates receipt of a message
QSL
RELAY (TO)
Transmit this message to all addresses
ROGER
I have received all of your last transmission satisfactorily
R
ROUTINE
Precedence ROUTINE
R
SAY AGAIN
Repeat all, or the following part of your last transmission.
IMI
SILENCE (3X)
Cease transmissions immediately. Silence
will be maintained until lifted (To be
authenticated when authentication
system in force).
HM HM HM
SILENCE LIFTED
Silence is lifted (To be authenticated when
authentication system in force)
SPEAK SLOWER
Your transmission is at too fast a speed.
Reduce speed of transmission.
THIS IS
This transmission is from
DE
TIME
Time or date-time group of the message follows
TO
The addresses immediately following are
addressed for action.
TO
UNKNOWN STATION
The identity of the station with whom I am attempting to communicate is unknown
AA
VERIFY
Verify entire message (or portion indicated) with the originator and send the correct version.
J
WAIT
I must pause for a few seconds
AS
WAIT OUT
I must pause for longer than a few seconds
AS
WILCO
Your last message (or message indicated) will
be complied with.
WORD AFTER
The word to which I have reference is the word following
WA
WORD BEFORE
The word to which I have reference is the word preceding
WB
WORDS TWICE
As a request or an order - Communication is difficult. Please send every word or phrase twice
QSZ
WRONG
Your last transmission was incorrect. The correct version is
ZWF
9-10 What are the dimensions of the ionosphere?
It extends from about 30 to 600 miles (50-965 km) above the earth’s surface.
9-10 Why is sky wave propagation only useful in the 300KHz - 30 MHz range?
-Frequencies below this range are too heavily attenuated by the atmosphere to make it back to the ground.
-Frequencies above this range are too high for refraction to occur in the ionosphere and the waves are lost to space.
9-10 What are the ionospheric layers during the day?
F2, F1, E, D.
9-10 What are the ionospheric layers during the night?
F and E.
9-10 Is the D layer useful for radio transmission and why/why not?
No. The D layer is considered a hindrance to long range communications as it absorbs radio waves in the MF and low HF bands. Frequencies in the upper HF band penetrate the D layer but are attenuated in so doing. Ionization in D layer is not high enough to significantly contribute to refraction, but atmosphere is still dense enough to cause absorption
9-10 What is the lowest usable layer and how far can it send signals?
The E layer is the lowest usable layer as it can refract signals up to 20 MHz.
It is generally good for communication ranges up to 620 miles.
9-10 Why is the F layer the best layer for sending radio signals?
When the sun is at its peak the ionization in the F layer is very high. This causes the F layer to break into two layers during the day, the F1 and F2 layers.
Since the atmosphere is very rarefied at these heights, the recombination of ions occurs very slowly after sunset. Therefore, a fairly constant ionized layer is present at all times.
9-10 What is the rule of thumb for HF frequencies?
High sun = high freq / Low sun = low freq
9-10 What are the factors affecting the return of a radio signal back to earth?
-Angle of transmission
-Frequency
-Signal strength
-Ion density
9-10 Explain the transmission angle?
As the angle of transmission is gradually increased, greater bending of the wave is required to return it to Earth.
For a given frequency, the highest angle at which the radio wave can be transmitted and still be refracted back to Earth is called the critical angle.
9-10 Explain how frequency affects refraction in the atmosphere?
Lower frequencies undergo more refraction but suffer from high attenuation.
Higher frequencies refract less but are less affected by attenuation.
For a given angle of transmission, the highest frequency which will be returned to Earth is called the critical frequency.
9-10 How does signal strength affect refraction?
All radio transmissions lose energy to attenuation. These losses are primarily due to spreading, absorption, scattering, and diffraction.
To overcome these losses over vast distances, HF transmissions must be broadcast at high energy levels.
The energy of a transmission can be increased in two ways:
increasing transmitter power (wattage) which requires large, expensive components and high electrical draw
for the same power, increasing the frequency effectively increases the energy of the signal. Therefore the higher frequency we can use with any given transmitter, the better HF communications we can expect.
9-10 How does ion density affect refraction?
The greater the ion density, the more refractive is the ionosphere.
Higher frequencies refract less than lower ones and without high ionization will not bend enough to return to Earth. With higher ion density, the ability of the ionosphere to refract radio signals increases and higher frequencies can be used. (sun’s up therefore frequencies up)
All frequencies undergo more refraction (i.e. signal is bent more) with higher ion density. Therefore the angle of transmission can be increased and the signal will still be returned to Earth.
9-10 What is the propagation path?
The path of radio waves when they are transmitted, or propagated, from one point on the Earth to another, or into various parts of the atmosphere.
9-10 What is the skip distance?
The distance between the transmitter and the point where the refracted sky wave returns to earth for the first time.
Transmission angle, signal strength and ionospheric density remaining the same, the skip distance will be dependent on the frequency.
9-10 What is the skip zone?
Distance between the end of the usable ground wave and the point where the first sky wave returns to earth.
9-10 How does fading affection the radio signal?
Fluctuations in the strength of the radio signal at the receiver due to interference
9-10 What is the maximum usable frequency?
The highest frequency that will give a skip distance equal to the distance from the transmitter to the intended receiving point.
9-10 What is the optimum working frequency?
The frequency which provides the most consistent comms, generally 85% of the MUF.
9-10 What are some considerations for frequency/station selection?
-Be aware of the a/c movement relative to the ground station as well as the time of day
-Always ask for a secondary frequency
-Note frequencies that have worked in the past
