Equipment Exam Flashcards
What types of waves are radio waves?
Sine Waves
What are the advantages of using FM radio?
- Resilience to noise: Any signal level variations will not affect the audio output
- Easy to apply modulation at a low power No boosting of the amplitude required
- Use of efficient RF amplifiers This means that for a given power output, less battery power is required and this makes the use of FM more viable for portable two-way radio applications
What do FM and AM stand for with regards to RT?
FM= Frequency Modulation
AM= Amplitude Modulation
What are the advantages of AM radio?
Stronger stations can override weaker or interfering stations, and don’t suffer from a capture effect found in FM.
- If a pilot is transmitting (Tx), a control tower can “talk over” that Tx and other aircraft will hear a somewhat garbled mixture of both Tx’s rather than just one or the other.
- A heterodyne (Squeal) will be heard, even if both Tx’s are received with identical signal strength. No such indication of blockage would be evident in an FM system
What is the frequency range and Wavelength of a VHF signal?
-30-300MHz
10m-1m
What is the frequency range and wavelength of a UHF signal?
300MHz-3GHz
1m-10cm
What is the amplitude of a radio wave?
The maximum displacement or value attained by the wave from it’s mean value during a cycle.
What is the wavelength of a radio wave?
The distance in metres or part of a metre between corresponding points in consecutive waves
What is the frequency of a radio wave?
The rate of repetition of the cycle in one second (oscillation). One cycle per second would be 1 hertz.
Ie how many oscillations/sec
What is velocity with regards to radio waves?
The speed in a given direction.
velocity= frequency x wavelength
What is a carrier wave?
A wave which carries the audio feed by modulating the audio wave and carrier wave together.
A carrier wave is produced by an oscillator
What type of modulation is used in Air Traffic and why?
AM
Due to the ability to overpower weaker radio signals.
Also produces a heterodyne when two or more stations are transmitting at once so that everyone knows when two or more stations are trying to transmit.
What is the ideal length of an aerial?
The same length as the wavelength of the wave being transmitted.
Can transmit proportions of the wave by being either half or a quarter of the wavelength instead to create more practicable lengths.
What is an amplifier?
It amplifies the strength of the received signal, needs a noise gate to prevent it from amplifying any static noise as well.
What is attenuation
The reduction in strength of a radio wave with time from the point of transmission.
As a wave attenuates the amplitude of the wave will decrease, the frequency and wavelength remain unchanged.
Longer wavelengths (lower frequencies) are less affected owing to interacting with less particles for a given distance and vice versa.
What are the wave-bands of the radio?
Freq Band. Spectrum of frequency. Wavelength
Very Low (VLF) 3-30KHz. 100-10km
Low (LF). 30-300KHz. 10-1km
Medium (MF). 300KHz-3MHz. 1km-100m
High (HF). 3-30MHz. 100-10m
Very High (VHF). 30-300MHz. 10-1m
Ultra High (UHF). 300MHz-3GHz. 1m-10cm
Super High (SHF). 3-30GHz. 10-1cm
Extremely High (EHF). 30-300GHz. 1cm-1mm
What is the frequency band for VLF and what is it used for?
3KHz-30KHz
100km-10km
Long range communications
What is the frequency band for LF and what is it used for?
30-300KHz
10km-1km
Reliable long range communications
Requires large aerials and high transmitter power
What is the frequency band for MF and what is it used for?
300KHz-3MHz
1km-100m
Used for reliable long range communications.
Very congested waveband
Used for NDB’s
What is the frequency band and wavelength for HF and what is it used for?
3-30MHz
100m-10m
Long range communications by day and night limited by diurnal (day and night) and seasonal variation of ionosphere.
RTF communications.
What is the frequency band and wavelength for VHF and what is it used for?
30-300MHz
10m-1m
Line of sight communications
Small aerial and transmitter power
Used for main ATC RTF frequencies
Free from static interference
Easy to suppress aircraft signals
Prone to ducting
VOR, VDF
Surveillance Radar
What is the waveband and wavelength for UHF and what is it used for?
300MHz-3GHz
1m-10cm
Line of sight comms
Used for surface communications with vehicles
Free from static interference
Prone to ducting
Used for ILS (DME element), DME’s, surveillance RADAR
What are the wave bands and wavelengths of SHF and EHF frequencies and what are they used for?
SHF is 3-30GHz 10cm-1cm
EHF is 30-300GHz 1cm-1mm
Short range communications
Precision, surveillance and airborne weather radar.
What is antenna shadowing?
When the transmitter aerial is shadowed from the receiver as the radio wave travels in a straight line so may be blocked by the curvature of the earth for example.
What happens when a wave is ducting?
It is bouncing off of a temperature inversion or under certain atmospheric conditions which may reflect VHF, UHF and SHF waves back to the ground and they will bounce around in this ‘duct’
What is propagation with reference to radio waves?
Similar to ducting but with low frequencies bending around objects that would normally shadow the signal. Can be heard a great distance from the source as the low frequencies mean lower attentuation.
What do we use RADAR for in Air Traffic Control?
Area Control
Approach Control
Aerodrome Control
- Air; traffic integration, approach monitoring
- Ground; Runway protection, monitoring ground hazards
How does RADAR work?
By calculating the time taken for a signal of a known speed to be recevied as an echo we can calculate the distance using the following equation.
Distance= (speed x time)/2
What does RADAR stand for?
Radio Detection And Ranging.
What are the two types of RADAR used in ATC?
Primary (PSR)
Secondary (SSR)
How does Primary RADAR work?
By sending out a pulse of electromagnetic energy and waiting for a reflection, as the speed of the wave is known (c) then the distance can be calculated easily.
distance= (speed x time)/2
This tells us how far away the object is and by combining this with the information about which way the RADAR was facing when the signal was received we can determine the position of an aircraft as well.
What waveband does RADAR operate in?
1mm-100cm
This is the same part of the electromagnetic spectrum as microwaves.
What wavelength is used for SMR?
2-3cm
What wavelength is used for Approach Radar?
3-10cm
What wavelength is used for Area RADAR?
23-50cm
What are PE’s?
Permanent Echoes
These are the position indications given by permanent objects in the area of operation of a RADAR, they can be used to check that the RADAR is still correctly aligned.
What is clutter and how is it formed?
Unwanted returns on a RADAR screen, these can be caused by ground, buildings, or weather (the rain droplets in clouds is what causes clouds to reflect RADAR)
What is a PSR blip?
The visual indication, in non symbolic form, on a situation display of an aircraft obtained by PSR.
What is a position indication?
A generic term for the visual indication, in non symbolic and/or symbolic form, on a situation display of the position of an aircraft, aerodrome, vehicle or other object.
What is a position symbol?
A visual indication in symbolic form, on a situation display, of the position of an aircraft, aerodrome vehicle or other object obtained after automatic processing of positional data derived from the source.
What is RADAR contact?
The situation which exists when the RADAR position of a particular aircraft is seen and identified on a situation display.
What is RADAR control?
Term used to indicate that RADAR-derived information is employed directly in the provision of ATC service.
What is a situation display
The screen. Displays the electronic information regarding position and movement of aircraft.
What are the three basic blocks of RADAR operation?
Transmission
Reception
Display
What is a duplexer?
Is a transceiver that can transmit and receive, but only does one or the other at a time.
What is the trigger unit?
It is the device that creates the pulses which are modulated by the modulator into the pulses that the RADAR actually sends out.
What is the unambigious range of a RADAR?
This is the maximum technical range from which a target echo or transponder response can be received. This determines the PRI.
What is the PRI of a RADAR?
The Pulse Repetition Interval
The interval between pulses necessary to receive a return from the unambigious range. ie how long would be needed between pulse replies to receive a signal from the RADARs maximum range.
This determines the PRF
What is the PRF?
The pulse repetition frequency
The number of pulses that can be trasmitted in a second.
Higher PRF the greater the clarity of the position return displayed as you get more ‘hits’ on it.
What is SSR?
Secondary Surveillance RADAR
RADAR that works by the sending an interrogation signal to the aircraft transponder which sends a reply to the station. The distance is calculated by the time taken for the response to tbe received and the direction is taken from the direction the RADAR is facing. The response can also contain height and identity information as well.
What are the frequencies for SSR?
The ground stations transmit the interrogation signal on 1030MHz
Aircraft transponder sends the reply on 1090MHz
What is the wavelength for SSR?
30cm
How does the interrogater actually interrogate the Transponder?
By sending a pair of pulses which are seperated by a certain time interval between each pulse.
8.5µs for Mode A
21µs for Mode C
The aircraft will then recognise this and send back the appropriate information.
How many binary bits are there in Mode A?
12 bits
This limits the possible amount of codes to 4096 discrete codes
How many Mode A codes are there?
4096
What are the different types of squawk codes?
- Discrete codes- Those assigned to individual aircraft
- Non Discrete- Single codes issued to numerous aircraft ie conspicuity
- Special codes- Applied to aircraft on certain occassions
What are ORCAM codes?
Originating Region Code Assignment Method
Codes are assigned depending on what participating area they come from.
It is designed to reduce RTF and cockpit work-load by allocating an SSR code which can be retained from take-off to touchdown.
What are the emergency special codes?
7500- Hijack/unlawful interference
7600- Radio Failure
7700- A/C emergency
What are conspicuity codes?
Codes assigned to individual positions to identify aircraft being controlled by a particular unit to another unit. Helps in coordinating between units.
How many bits are there for Mode C?
11
this is because the numbers 8 and 9 are now required.