Double Sideband Modulation

Question 1

Modulation

Answer 1

process where a message signal changes a carrier signal to be transmitted through a communication channel

Question 2

Baseband

Answer 2

a system without modulation, the signal goes directly into the channel

Question 3

Choice of modulation technique depends on

Answer 3

1) Characteristic of the application
2) Channel characteristic
3) Performance of the entire communication system

Question 4

What do we look at to pick the best modulation technique?

Answer 4

Bandwidth, noise performance, cost/complexity, power efficiency

Question 5

Channel bandwidth needed for DSB modulation?

Answer 5

2W (2 times the bandwidth of the message signal must be available in the channel)

Question 6

Double Side Band Modulation process

Answer 6

Multiple the message signal by a carrier signal for transmission
Multiple the received signal by a copy of the carrier signal and low pass filter to get the original message signal back

Question 7

Coherent demodulation

Question 8

Techniques to generate the coherent demodulation
carrier necessary for the demodulation of DSB signals

Answer 8

Square the received
DSB signal
Costas Phase-Locked
Loop

Question 9

Modulation

Answer 9

the systematic variation of some attribute
of the carrier, such as amplitude, phase, or frequency, in accordance with a function of the message signal

Question 10

reasons for using a carrier

Answer 10

(1) for ease of radiation, (2) to reduce noise and interference, (3) for channel assignment,
(4) for multiplexing or transmission of several messages over a single channel, and (5) to
overcome equipment limitations

Question 11

linearly modulated carrier

Answer 11

𝑥𝑐 (𝑡) = 𝐴(𝑡) cos(2𝜋𝑓𝑐 𝑡)

Question 12

DSB modulated signal

Answer 12

𝑥𝑐 (𝑡) = 𝐴𝑐𝑚(𝑡) cos(2𝜋𝑓𝑐 𝑡)

Question 13

Spectrum of DMB modulated signal

Answer 13

𝑋𝑐 (𝑓) = 1/2𝐴𝑐𝑀(𝑓 + 𝑓𝑐 ) + 1/2𝐴𝑐𝑀(𝑓 − 𝑓𝑐 )

Question 14

Amplitude modulated signal

Answer 14

𝑥𝑐 (𝑡) = 𝐴𝑐 [1 + 𝑎𝑚𝑛(𝑡)] cos(2𝜋𝑓𝑐 𝑡)

Question 15

Normalized message signal

Answer 15

𝑚𝑛(𝑡) = 𝑚(𝑡)/|min[𝑚(𝑡)]|

Question 16

Envelope detection time constant

Answer 16

The appropriate value for the
time constant is related to the carrier frequency and to the bandwidth of 𝑚(𝑡). In practice,
satisfactory operation requires a carrier frequency of at least 10 times the bandwidth of 𝑚(𝑡),
which is designated 𝑊 . Also, the cutoff frequency of the RC circuit must lie between 𝑓𝑐 and
𝑊 and must be well separated from both