Book 4

Question 1

What are the Advantages of Digital Signals?

Answer 1

• Greater quantities of data can be transferred quicker
• Digital signals are easily differentiated from noise
• Allows for Multiplexing
• Encryption is easier
• Parity bits

Question 2

What are the Disadvantages of Digital Signals?

Answer 2

Requires a much greater bandwidth.

Question 3

What is Quantization Error?

Answer 3

The difference between the actual measured amplitude and digital code.

Question 4

What is Aliasing?

Answer 4

The production of fictitious or ghost signals which is at a lower frequency than the original

Question 5

What is Shannon’s Rule?

Answer 5

Shannon’s rule states that a signal must be sampled at a rate of at least twice the highest input frequency if the signal is to be faithfully reconstructed from the digital samples

Question 6

Draw Amolitude Shift Keying (ASK)

Answer 6

~~~»>~~~~»>~~~»>

Question 7

Draw Frequency Shift Keying (FSK)

Answer 7

Stretched frequency, tight frequency, stretched frequency, tight frequency

Question 8

Draw Phase-Shift Keying

Answer 8

Phase, anti-phase, phase, anti phase

Question 9

What are the advantages of Multiplexing?

Answer 9

• Increased message handling capacity
• Sharing a given bandwidth between several signal sources

Question 10

What are the Three ways to Multiplex?

Answer 10

• Time Division Multiplexing (TDM)
• Frequency Division Multiplexing (FDM)
• Code Divison Multiplexing (CDM)

Question 11

What is Time Division Multiplexing (TDM)?

Answer 11

People take turns speaking

Question 12

What is Frequency Division Multiplexing (FDM)?

Answer 12

People speak at different pitches

Question 13

What is Code Division Multiplexing (CDM)?

Answer 13

People use different languages

Question 14

What is Spread Spectrum Systems?

Answer 14

A technique that takes a narrow band signal and spreads it over a broader portion of the radio frequency band

Question 15

What are the Three advantages of Spread Spectrum transmission?

Answer 15

• Highly resistant to noise and interference
• Difficult to intercept
• Share a frequency band with many types of conventional transmissions

Question 16

What is Frequency Hopping Spread Spectrum?

Answer 16

A method of transmitting radio signals by rapidly switching a carrier amount many frequency channels.

Question 17

What is a Word of Day (WoD)?

Answer 17

A pseudo random code with oh indicates the pattern in which a frequency will ‘hop’ between the frequencies on a channel.

Question 18

What is Time of Day (ToD)?

Answer 18

A way of synchronising the real time clock of the transmitting radio and receiving radio before the A/J mode is activated.

Question 19

What is Direct Sequence Spread Spectrum?

Answer 19

When the data is mixed with a pseudo random code to spread the energy of the original code into a much wider band.

Question 20

What are the Two Advantages of Direct Sequence Spread Spectrum?

Answer 20

• Very difficult to jam
• Impossible for the enemy to listen to a data message

Question 21

What are the Advantages of Satellite Communications?

Answer 21

• Smaller aerial required
• More channels available
• Less transmitter power is required
• Transmission is not affected by the ionosphere.

Question 22

What is Geosynchronous Orbit?

Answer 22

For an observer at a fixed location on Earth, a satellite returns to exactly the same place in the sky at exactly the same time each day.

Question 23

What is Geostationary Orbit?

Answer 23

Where a satellite appears stationary with respect to a fixed point on the rotating Earth.

Question 24

What is a Footprint?

Answer 24

The area on Earth that the satellite can ‘see’.

Question 25

What are the Two major problems with SATCOM to aircraft?

Answer 25

• Satellite Tracking
• Aerial Position
• Doppler Shift