Book 4 Flashcards
(25 cards)
What are the Advantages of Digital Signals?
- Greater quantities of data can be transferred quicker
- Digital signals are easily differentiated from noise
- Allows for Multiplexing
- Encryption is easier
- Parity bits
What are the Disadvantages of Digital Signals?
Requires a much greater bandwidth.
What is Quantization Error?
The difference between the actual measured amplitude and digital code.
What is Aliasing?
The production of fictitious or ghost signals which is at a lower frequency than the original
What is Shannon’s Rule?
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
Draw Amolitude Shift Keying (ASK)
~~~»>~~~~»>~~~»>
Draw Frequency Shift Keying (FSK)
Stretched frequency, tight frequency, stretched frequency, tight frequency
Draw Phase-Shift Keying
Phase, anti-phase, phase, anti phase
What are the advantages of Multiplexing?
- Increased message handling capacity
- Sharing a given bandwidth between several signal sources
What are the Three ways to Multiplex?
- Time Division Multiplexing (TDM)
- Frequency Division Multiplexing (FDM)
- Code Divison Multiplexing (CDM)
What is Time Division Multiplexing (TDM)?
People take turns speaking
What is Frequency Division Multiplexing (FDM)?
People speak at different pitches
What is Code Division Multiplexing (CDM)?
People use different languages
What is Spread Spectrum Systems?
A technique that takes a narrow band signal and spreads it over a broader portion of the radio frequency band
What are the Three advantages of Spread Spectrum transmission?
- Highly resistant to noise and interference
- Difficult to intercept
- Share a frequency band with many types of conventional transmissions
What is Frequency Hopping Spread Spectrum?
A method of transmitting radio signals by rapidly switching a carrier amount many frequency channels.
What is a Word of Day (WoD)?
A pseudo random code with oh indicates the pattern in which a frequency will ‘hop’ between the frequencies on a channel.
What is Time of Day (ToD)?
A way of synchronising the real time clock of the transmitting radio and receiving radio before the A/J mode is activated.
What is Direct Sequence Spread Spectrum?
When the data is mixed with a pseudo random code to spread the energy of the original code into a much wider band.
What are the Two Advantages of Direct Sequence Spread Spectrum?
- Very difficult to jam
- Impossible for the enemy to listen to a data message
What are the Advantages of Satellite Communications?
- Smaller aerial required
- More channels available
- Less transmitter power is required
- Transmission is not affected by the ionosphere.
What is Geosynchronous Orbit?
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.
What is Geostationary Orbit?
Where a satellite appears stationary with respect to a fixed point on the rotating Earth.
What is a Footprint?
The area on Earth that the satellite can ‘see’.
