BASIC RADIO PROPARGATION Flashcards
CONTINUOS POWER IN A PULSE MODULATION
~AVG POWER CONSUMED OVER TIME INCLUDIGN THE PERIODS OF NO TRANSNSMISSION
PULSE POWER
POWER CONTAINED WITHIN A PULSE
WHAT IS AMPLITUTDE MODULAITON
The info that is impressed onto the carrier wave by altering the ampitude f the carrier wave.
Is suceptibile to noise
What is frequncy modulation
~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
PHASE modualtion
~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
Single side band(SSB)
~Remove one sideband increases efficiency
~in aviation is use for HF and VOLMET
SUPPRESSED CARRIER WAVE(SCW)
~further energy saving by removing the transmitted carrier wave
~requires a BEAT FREQUENCY OSCILLATOR (BFO) at the receiver to re insert the carrier
SIGNAL CALSSIFICATION
~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)
Antenna
~Electrical device which converts electrical power into radio waves and vice versa
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POLARISATION
~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
Dipole antenna
~simplest type of antenna
~wire of length equal to 1/2 wavelentgh
~omnidirectional
~cone of confusion overhead
Loop antenna
~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
Parabolic antenna
~amplifies weak signals
~used in old weather radar
~highly directional
Slotted planar array antenna
~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
Helical antenna
~omnidirectional: normal mode (VHF and comms)
~directional, axial mode(GPS)
Produces a circular /elliptical plane of polarisation