BASIC RADIO PROPARGATION Flashcards

1
Q

CONTINUOS POWER IN A PULSE MODULATION

A

~AVG POWER CONSUMED OVER TIME INCLUDIGN THE PERIODS OF NO TRANSNSMISSION

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2
Q

PULSE POWER

A

POWER CONTAINED WITHIN A PULSE

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3
Q

WHAT IS AMPLITUTDE MODULAITON

A

The info that is impressed onto the carrier wave by altering the ampitude f the carrier wave.
Is suceptibile to noise

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4
Q

What is frequncy modulation

A

~The info that is impressed onto the carrier wave by altering the frequency of the carrier of the wave.

~Less suceptible to noise (bc the noise changes the amplitude ,since in freq modulation the amplitude is constant ,it can detect the noise by escluding the different amplitude )
~More efficeint
~Used in commercial radio

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5
Q

PHASE modualtion

A

~a modulation used in GPS where the phase of the carrier wave is reversed
~requires complex demodulator
~used in gps
~reverses phase of the carrier

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6
Q

Single side band(SSB)

A

~Remove one sideband increases efficiency
~in aviation is use for HF and VOLMET

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7
Q

SUPPRESSED CARRIER WAVE(SCW)

A

~further energy saving by removing the transmitted carrier wave
~requires a BEAT FREQUENCY OSCILLATOR (BFO) at the receiver to re insert the carrier

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8
Q

SIGNAL CALSSIFICATION

A

~N0N: carrier without modulation (used by NDB)
~A1A: carrier with keyed modulation (used by NDB)
~A2A:carrier with amplitude modulated morse code(used by NDB)
~A3E:carrier with amplitude modulated speech (used by VHF comms)

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9
Q

Antenna

A

~Electrical device which converts electrical power into radio waves and vice versa
~

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10
Q

POLARISATION

A

~describes the plane of oscillation of the elctrica component of a wave with regard to its direction of propargation
~determined by the orientation of the antenna

~linear :vertical or horizontal
~circular: requires helical antenna
Elliptical :requires helical antenna
Received antenna must be aligned in the same way as the transmitter to properly receive the transmitted signal

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11
Q

Dipole antenna

A

~simplest type of antenna
~wire of length equal to 1/2 wavelentgh
~omnidirectional
~cone of confusion overhead

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12
Q

Loop antenna

A

~good at direction finding
~used in automatic direction finding (ADF)
~looks for the null position (nop hase difference either side of the loop)
~requuiers a second antenna to eliminate the one of the nulls

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13
Q

Parabolic antenna

A

~amplifies weak signals
~used in old weather radar
~highly directional

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14
Q

Slotted planar array antenna

A

~used in modern a/c
~highly directional
~sereis of slots which are scanned electronically
~more e3fficent than a parabolic antenna drastically reduces side lobes concentrating energy into the main beam

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15
Q

Helical antenna

A

~omnidirectional: normal mode (VHF and comms)
~directional, axial mode(GPS)

Produces a circular /elliptical plane of polarisation

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16
Q

Factors affecting propagation

A

~REFLECTION: abrupt change in directionwhen hits a surface
(Caused by: terrain,builidngs,a/c water droplets)

~REFRACTION:a change in direction of wave caused by a change in propagation speed,when moving from one medium to another.

~DIFFRACTION: bending of waves around objectes or through apertures
(Tendency of some waves to follow the earth curvature)

~ABSORPTION: the transfer of a waves energy to the matter it has encountered

~ATTENUATION:gradual loss of energy of a wave propagating through a medium

~MULTI PATH PROPAGATION:when one signal is reflected from surfaces between the transmitter and receiver and arrives at the receiver via more than path simultaneously.

~SUPERPOSITON: combination of two or more similar waves

~INTERFERENCE: the result of superpositon of two waves,can be constructive or distructive

~FADING: interfence of signal resulting in changes in signal strength and polarisation ,caused by multi path ,weather

17
Q

Static interfence

A

~natural ,stops at VHF
~man made ,VHF and above

18
Q

WAVE PROPAGATION

A

~SKY WAVES: EM waves refracted by the E and F layers of thee ionosphere
(VLF,LF,MF,HF ) possible sky wave at night therefore ,susceptible to fading

~GROUND WAVES : travelling along the surface of the earth

~SPACE WAVES :travelling directly trhough the air from the transmitter to receiver.
(VHF,UHF,SHF,EHF). VHF is limited din range bc is not reflected by the ionosphere and does not have surface wave.

19
Q

SPACE WAVES

A

MAX range NM : 1,23 x ( sqroot tx (ft) + sqroot Rx (ft) )

20
Q

IONOSPHERE

A

60/400km above the surface
Vetrically structered into 3 layers&raquo_space;D,E,F

~UV,X RAYS RADIATION
~radiation waves passing through ionosphere layers are attenuated ,LOWER FREQ experience LESS attenuation

21
Q

Layers

A

~D LAYER: Lowest layer,thickness reduces at night,MF and HF waves significantly attenuated,main cause of daytime absorption of HF waves.

~E LAYER: refracts EM waves back to the surface SKY WAVE,weakens at night base rises increasing range of refracted waves,during periods of intense solar activty SPORADIC E layers may form,capbale of refracting VHF

~F LAYER: refracts waves back to the surface SKY WAVE,comprises a single F2(higher) layer at night,sperate F1 (lower) layer forms during day

22
Q

SKY WAVES

A

~DEAD SPACE/ SKIP ZONE: distance between the limit of the surface wave and the sky wave

~SKIP DISTANCE: distance bewteen transmitter and the first sky wave return arrives