What types of waves are radio 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?
What is the frequency range and wavelength of a UHF signal?
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?
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?
Long range communications
What is the frequency band for LF and what is it used for?
Reliable long range communications
Requires large aerials and high transmitter power
What is the frequency band for MF and what is it used for?
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?
Long range communications by day and night limited by diurnal (day and night) and seasonal variation of ionosphere.
What is the frequency band and wavelength for VHF and what is it used for?
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
What is the waveband and wavelength for UHF and what is it used for?
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?
-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?