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28 Cards in this Set
- Front
- Back
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The HF frequency covers what range of frequencies?
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3-30Mhz
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The wavelength corresponding to a frequency of 339kHz is?
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885m
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The wavelength corresponding to a frequency of 9875MHz is?
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3.03cm
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The frequency which corresponds to a wavelength of 2.4m is?
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125Mhz
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What is the length of a dipole?
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A dipole is one-half of the wavelength
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When an RF signal is radiated from a vertical antenna, the H field will be in the _____ plane, the E field will be in the _____ plane and the receiver antenna should be in the ______ plane.
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horizontal, vertical, vertical
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Which component of an electromagnetic wave defines the plane of polarisation?
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The oriention of the electrical (E) component determines the plane of polarisation.
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I a basic radio transmitter, what is the purpose of the modulator?
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The modulator superimposes the modulating signal onto the carrier signal.
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What is the advantage in a GPS satellite transmission of circular ploarisation?
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The dynamics of the transmitter and receiever both moving require circular polarisation to ensure maximum signal strength at all times under these circumstances.
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The distance between the transmitter and the first returning sky wave is know as?
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Minimum skip distance
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Which equipment used a slotted (flat plate) antenna?
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Airborne weather radar
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A frequency of 4Ghz will have a wavelength of ______ which is in the _____ frequency band.
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7.5cm - SHF
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Atmospheric ducting is most likely to occur closer to the surface of the earth when?
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There is a marked inversion and a marked decrease in humidity with height.
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Why is an NDB transmission not subject to skywave interference by day?
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The D layer of the ionosphere by day completely attentuates and LF/MF frequency signals and so no skywaves occur
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As the frequency of an HF transmission is increased, the dead space will?
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Increase due to increasing minimum skip distance and decreasing surface wave range.
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When is the ionosphere strongest?
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By day, in summer at low lattitudes.
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Which type of modulation is used in VHF telephony?
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A3E - double side band amplitude modulation
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What are the two effects of the ionospheric layers in relation to a radio wave?
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They cause bending (refraction) and attentuation
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Which type of propagation applies to VHF transmission?
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Direct/Space Wave - Line of sight
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The advantage of single-sideband SSB over double-sideband is?
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The bandwidth is halved which reduces power consumption and improves signal to noise ratio
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What is the approximate range of heights of the ionosphere?
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60 to 400km
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What is the definition of amplitude?
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The maximum deflection in oscillation (wave)
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When conveying the same intelligence using FM and AM techniques, which method would require a wider bandwidth receiver?
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FM
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Which frequency bands are particularly susceptible to static interference?
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Lower frequency bands (LF/MF)
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What is the cause of fading?
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Variations of signal stength at the receiver resulting from surface and skywave propogation.
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What is the formula for calculating the maximum theoretical range of a transmision in nautical miles?
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1.23 x ((sqrt trans heigh) + (sqrt rec height))
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What is the key feature of a parabolic radar reflector?
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It turns a point source of energy into a frontal wave of energy
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What frequency bands does ILS equipment occupy?
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VHF (Localiser & Markers)
UHF (Glide path) |
