Intro (10-05-18)

Question 1

What kind of current is required to produce a electromagnetic wave?

Answer 1

AC, due to the changing magnetic field around the wire.

Question 2

What orientation and length of aerial is best for picking up a vertically polarised radio wave?

Answer 2

a vertical aerial of length similar to that of the wave

Question 3

What is the plane of polarisation for radiomagnetic waves in aviation?

Answer 3

Vertical

Question 4

What is the frequency range of radio waves?

Answer 4

3kHz - 300GHz

Question 5

What is the speed of light?

Answer 5

3x10^8 m/s

Question 6

How are frequency bands for radio waves separated?

Answer 6

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)

Question 7

What are the advantages and disadvantages of FM signals?

Answer 7

Advantages:

Less susceptible to static

Disadvantages:

Need more power

Need more bandwidth

Need more complex receiving equipment

Question 8

What is static?

Answer 8

signal interference from external sources, such as the big bang, TSs etc

Question 9

What is noise?

Answer 9

signal interference from internal sources, such as issues in equipement like manufacturing defects.

Question 10

What are sidebands?

Answer 10

signals created in frequencies surrounding the main signal frequency through modulation.

Question 11

What is an SSB?

Answer 11

A signal that halves with amount of sidebands created by halving the bandwidth used for the signal.

Question 12

What do HF comms need in order to use SSB?

Answer 12

A specially designed SSB receiver/transmitter.

Question 13

What is the basic structure of a radio transmitter?

Answer 13

Microphone -> Amplifier -> Modulator <- RF Oscillator

RF Amplifier <-

Antenna <-

Question 14

What is the structure of a basic radio receiver?

Answer 14

Antenna -> RLC circuit (tuner) -> RF Amplifier -> demodulator -> AF Amplifier -> speaker

Question 15

What is a demodulator called in FM signals?

Answer 15

discriminator.

Question 16

What do the 3 symbols mean in the classification of signal emission?

Answer 16

First symbol - Type of modulation

Second symbol - Nature of modulating signal

Third symbol - Nature of transmited signal

Question 17

What is a polar diagram?

Answer 17

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.

Question 18

What length of a dipole antenna allows for max efficiency?

Answer 18

Half the wavelength of the signal to be received.

Question 19

What kind of frequencies do parabolic antenna mainly transmit?

Answer 19

UHF, SHF and EHF

Question 20

What are the advantages of planner array/slotted scanner?

Answer 20

Less side lobes

Narrower beams.

Question 21

What is a phase array?

Answer 21

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.