Flashcards
1. Basic Principles
Cards in this deck (81)
- 1Define Amplitudethe maximum displacement from the mean
- 2what is the maximum amplitude positive or negative known asthe peak value
- 3define a cycleone complete revolution between two identical points on a wave
- 4define frequencythe number of cycles per second
- 5what is frequency measured inhertz
- 6define a Hznumber of cycles per second
- 7define wavelengthdistance traveled by a wave in one complete cycle
- 8what is the distance between the peak and troughpeak to peak amplitude
- 9what is the relationship between wavelength and frequencythey are inversely proportional
- 10what is the equation involving frequency and wavelengthwavelength= speed of sound/ frequency in khz
- 11what is the speed of sound300 000 km/second
- 12define a phasedescribes a particular point in a cycle
- 13what does it mean to be out of phasewhen wave are no in sync
- 14how do we measure by how much one wave is out of phaseyou take the point on one wave and compare it to the same point on the second wave.
- 15what can you say about the propagation of electromagnetic wavesthey have 2 different planes, one electrical, one magnetic. These planes are perpendicular to each other as well as being perpendicular to the direction of propagation.
- 16define polarisationdescription of the orientation of the plane of oscillation of the electric field
- 17define vertical polarisationwhen transmission is made from a vertical aerial, the oscillation of the electrical plane is vertical
- 18in vertical polarisation, in what way does the magnetic field operatehorizontally
- 19define horizontal polarisationwhen the line of transmission is made from a horizontal ariel, the electrical component travels in a horizontal plane
- 20describe the oscillation of the magnetic component of an electromagnetic wave in horizontal polarisationvertical
- 21what radiation on an aircraft often uses horizontal polarisationILS and VOR
- 22define circular polarisationthe electrical and magnetic components spin around the axis of advance at a rate equal to their frequency.
- 23what are the two types of polarisation1. linear
2. circular - 24what is circular polarisation also referred to aselliptical
- 25define Antennaa wave type transducer that converts electrical energy in the form of an AC into an Electromagnetic wave
- 26what is the optimum wire length in a simple antennawire length 1\2 that of the wavelength
- 27give four common types of directional antennas LPSH lovely people smell happyloop antenna
parabolic antenna
slotted planar array
helical antenna - 28define polar diagramsa representation of the radiation pattern of a transmitting aerial
- 29what does omnidirectionalwhen looking overhead a circular motion around the transmitter
- 30define modulationthe process of impressing a message into a carrier wave
- 31what are the five different types of modulation-keying
-phase
-pulse
-amplitude
-frequency - 32describe keyingyou impress a message by interrupting the carrier waves, into short/slightly longer breaks.
- 33what is keying used inmorse code
each letter of the alphabet has a corresponding sequence of dots/dashes - 34describe pulse modulationthe radio wave is switched on/off at regular intervals, forming pulses of radio waves
- 35describe amplitude modulationthe amplitude of the carrier wave is varied in accordance with the amplitude of the wave containing the message.
- 36what is it that must not be changed in amplitude modulationthe frequency
- 37modulation depth is calculated by what equationAmplitude of Audio Frequency/ Amplitude of carrier wave
x 100 - 38what do you have to be careful of when looking at amplitude modulation?that you do not cause overmodulation
- 39what is caused by overmodulationdistortion
- 40define frequency modulationimpressing a message on a carrier wave by altering the frequency.
the degree of frequency variation depends on the amplitude of the modulating audio signal - 41what happens in FM when the amplitude is positivethe frequency of the carrier wave is increased proportionally
- 42what happens in FM when the amplitude is negativethe frequency of the carrier wave is decreased proportionally
- 43Advantages of FM over AM include: costFM transmitters are cheaper
- 44Advantages of FM over AM include: difficultyFM transmitters are simpler
- 45Advantages of FM over AM include: powermodulation power is lower
- 46Advantages of FM over AM include: receptionreception is practically static free as it is operative in the VHF band
- 47Advantages of FM over AM include: polarisationas the transmission is usually horizontally polarised , it suffers less from weather induced static, which is vertically polarised
- 48disadvantages of FM (complexity)FM receivers are more complex than AM receivers
- 49disadvantages of FM (bandwidth)fm transmission calls for a wider frequency band
- 50in what band do FM broadcasts operate in ?VFH band
- 51define phase modulationin phase modulation, when the amplitude increases, the phase of the carrier wave is reversed
- 52what is phase modulation also known asphase shift keying
- 53what is the main disadvantage of Phase modulationusually only used for data signals
- 54what is the main advantage of phase modulationsuperior resistance to fading and interference
- 55what are sidebansdsupper and lower band of frequency radiated when a wave is modulated
- 56when do sidebands occurwhenever a carrier is modulated by a frequency lower than itself.
usually during amplitude modulation - 57what does SSB stand forsingle side band
- 58what does the first symbol stand for :type of modulation of the main cariier
- 59what does the second symbol stand fornature of the signal modulating the main carrier
- 60what does the third symbol stand forthe nature of the signal to be transmitted
- 61what 3 phenomena affects an EM waves path-refraction
-reflection
-diffraction - 62define refractionchange of speed, and therefore change in direction when an EM waves enters a different medium to the one it is currently travelling in
- 63example of refraction includesa pen appearing disjointed when placed in a glass of water
- 64define reflectionwhen an object is bounced off a flat surface
- 65what are the 3 types of refractioncoastal refraction
atmospheric refraction
ionospheric refraction - 66define coastal refractionchange of direction when the radio wave crosses the coast, due to different levels of attenuation and different speeds of radio waves over land and sea
- 67define atmospheric refractionchanges in direction occur due to variations in temp, pressure, density and humidity
- 68when is atmospheric refraction at its largestat low altitudes
- 69what is the most extreme cause of atmospheric refractionduct propagation
- 70when does duct propagation occurat exceptional levels of attenuation
- 71define ionospheric refractionwhen changes in direction occur when the radio waves passes through the ionised layers of the earths upper atmosphere, and are bent back downwards towards the earth.
- 72what is the ave that ionospheric refraction is associated with?skywaves
- 73what are the three types of wavesky waves
surface waves
direct waves - 74define reflectionwhen a radio wave bounces off a solid surface
- 75what is the main issue commonly associated with reflectionwhen used in aircrafts it is common for waves to be reflected off terrain, and can result in the same wave arriving out of phase with each other and therefore cause fading
- 76define attenuationloss of power or signal strength suffered by radio waves when they pass through matter or over a surface
- 77what can attenuation also be compared toabsorption
- 78when does surface attenuation increase?it increases with an increase in frequency
- 79what can radar attenuation also be called?atmospheric attenuation
- 80describe the doppler effectthe apparent increase or decrease from of an electromagnetic wave's frequency depending on relative motion between the transmitter and receiver
- 81—
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- RNAV Flashcards on 1. Basic Principles, created by Ella Davies on 19/02/2018.
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- Ella Davies
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