Lecture 11 - Modulation Technique Flashcards
1
Q
What is modulation and what are the 3 basic modulation techniques?
A
- Modulation techniques are methods used to encode information so that it can be sent over a medium.
- The 3 basic modulation techniques are: Amplitude Modulation (AM), Frequency Modulation (FM) and Phase Modulation (PM)
2
Q
What is a carrier signal? [2]
A
- A carrier signal is a single frequency that is used to carry the intelligence (data) or the binary data signal.
- For digital, the intelligence is either a 1 or 0.
3
Q
What is AM?
A
AM modulation operation is equivalent to multiplying the carrier signal by the binary data signal to obtain the resultant “AM” carrier (signal).
4
Q
Advantage of AM [1]
A
Simple to design.
5
Q
Disadvantage of AM [2]
A
- Noise spikes on transmission medium interfere with the carrier signal.
- Loss of connection is read as 0s.
6
Q
What is FM? [2]
A
- Frequency Modulation modifies the frequency of the carrier to represent the 1s or 0s.
- It employs to carrier waves (of different frequencies)
7
Q
Advantage of FM [2]
A
- Immunity to noise on transmission medium.
* Always a signal present. Loss of signal easily detected.
8
Q
Disadvantage of FM [2]
A
- Requires 2 frequencies.
* Detection circuit needs to recognize both frequencies when signal is lost.
9
Q
Advantage of PM [2]
A
- Only 1 frequency used
* Easy to detect loss of carrier
10
Q
Disadvantage of PM [2]
A
- A reference carrier signal is required at the receiver against which the phase of the received signal is compared.
- Complex circuitry required to generate and detect phase changes.
11
Q
What is PM? [4]
A
- Phase Modulation modifies the phase of the carrier to represent a 1 or 0.
- The carrier phase is switched at every occurrence of a 1 bit but remains unaffected for a 0 bit. The phase of the signal is measured relative to the phase of the preceding bit.
- The bits are timed to coincide with a specific number of carrier cycles
- . A phase coherent is additionally considered to obtain the resultant PM signal.
