Intro (10-05-18) Flashcards
What kind of current is required to produce a electromagnetic wave?
AC, due to the changing magnetic field around the wire.
What orientation and length of aerial is best for picking up a vertically polarised radio wave?
a vertical aerial of length similar to that of the wave
What is the plane of polarisation for radiomagnetic waves in aviation?
Vertical
What is the frequency range of radio waves?
3kHz - 300GHz
What is the speed of light?
3x10^8 m/s
How are frequency bands for radio waves separated?
in factors of 10:
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VLF - Very low (3 - 30kHz)
LF - Low (30 - 300kHz)
MF - Medium (300kHz - 3MHz)
HF - High (3 - 30MHz)
VHF - Very high (30 - 300MHz)
UHF - Ultra high (300MHz - 3GHz)
SHF - Super high (3 -30GHz)
EHF - Extremely high (30 - 300GHz)
What are the advantages and disadvantages of FM signals?
Advantages:
Less susceptible to static
Disadvantages:
Need more power
Need more bandwidth
Need more complex receiving equipment
What is static?
signal interference from external sources, such as the big bang, TSs etc
What is noise?
signal interference from internal sources, such as issues in equipement like manufacturing defects.
What are sidebands?
signals created in frequencies surrounding the main signal frequency through modulation.
What is an SSB?
A signal that halves with amount of sidebands created by halving the bandwidth used for the signal.
What do HF comms need in order to use SSB?
A specially designed SSB receiver/transmitter.
What is the basic structure of a radio transmitter?
Microphone -> Amplifier -> Modulator <- RF Oscillator
RF Amplifier <-
Antenna <-
What is the structure of a basic radio receiver?
Antenna -> RLC circuit (tuner) -> RF Amplifier -> demodulator -> AF Amplifier -> speaker
What is a demodulator called in FM signals?
discriminator.
What do the 3 symbols mean in the classification of signal emission?
First symbol - Type of modulation
Second symbol - Nature of modulating signal
Third symbol - Nature of transmited signal
What is a polar diagram?
A diagram in which a point of origin is surrounded by a curve whose radius at any given point is proportional to the magnitude of some property measured in the direction of that point.
What length of a dipole antenna allows for max efficiency?
Half the wavelength of the signal to be received.
What kind of frequencies do parabolic antenna mainly transmit?
UHF, SHF and EHF
What are the advantages of planner array/slotted scanner?
Less side lobes
Narrower beams.
What is a phase array?
A series of dipoles that are fed with the same signal but in different phases in order to electronically “steer” a signal without actually turning the antenna.
