EXPERIMENT 6: SSBSC modulation and demodulation

Question 1
The signal out of the SSB modulator is highly unlikely to be an SSB signal at this stage.
What are two reasons for this? Tip: If you’re not sure, one of them can be worked out by
reading the preliminary discussion.
The signal from an SSB modulator's Adder module is unlikely to be a perfect SSB wave for two reasons:
poor SSB generation filtering and system nonlinearities, particularly during the frequency translation step.
Practical filters may have flaws such as passband rippling or poor stopband attenuation, resulting in signal
distortion. The second cause is related to potential nonlinearities in the frequency translation step (up or
down conversion stages) of an SSB modulator. These nonlinearities might result in mixing products or
harmonics, destroying the symmetry necessary for an SSB signal.

Question 2
How many sinewaves does this SSB signal consist of?
only one sinewave

Question 3
For the given inputs to the SSB modulator, what two frequencies can this signal be? Tip:
If you’re not sure, see the preliminary discussion.
90kHz or 110kHz

Question 4
What is the relationship between the original message and the recovered message?
As a result, the relationship between the original message signal and the recovered message is one of
correspondence and resemblance, with efforts made to ensure that the recovered message accurately
mimics the original.

EXPERIMENT 7: Frequency modulation

Question 2
What is the relationship between the FM signal’s frequency deviation (that is, the VCO
module’s output) and the amplitude of the message?
Both are in direct proportion. The frequency oscillator affects the frequency of its output by applying an
input voltage.

Question 3
What is the relationship between the FM signal’s frequency deviation and the frequency of
the message? Tip: This relationship may not be observable with the present set-up.
The frequency fluctuation of the FM signal is directly related to the frequency of the message signal. This
indicates that when the message signal's loudness grows, so does the frequency deviation of the FM
signal.

Expirement 8: FM demodulation
Question 1
Why is the FM signal no-longer a sinewave? Tip: If you’re not sure, see the preliminary
discussion.
FM refers to the information signal that appears as a frequency variation in the carrier signal. As a result,
the frequency of the FM signal fluctuates with the input signal, hence it cannot be a sinewave with a
constant frequency unless no information is being transmitted.

Question 2
What type of waveform does the Comparator output?
A comparator output is always a square wave, and its ON-OFF time ratio is defined by the amplitude of the
input signal and the threshold we use to compare it against.

Question 3
What does this tell us about the DC component of the comparator’s output?
The dc component of comparator output reveals how distant our input signals' average value is from the
threshold value we are comparing against.

Question 4
What type of waveform does the ZCD output?
the waveform of ZCD output is square wave.

Question 5
As the FM signal changes frequency so does the ZCD’s output. What aspect of the signal
changes to achieve this?
 Neither the signal’s mark nor space
 Only the signal’s mark
 Only the signal’s space
 Both the signal’s mark and space

Question 6
What does this tell us about the DC component of the comparator’s output?
The comparator's square waveform shows no substantial CD bias, suggesting that the DC component of
the original FM signal has been properly eliminated. This absence of DC compensation means that
fluctuations in the output frequency of the zero cross detector, which correspond to the varied frequency of
the FM signal, are only impacted by the frequency components of the signal rather than the DC offset.

Question 7
If the original message is a sinewave instead of a variable DC voltage, what would you
expect to see out of the Baseband LPF?
If the originating message is a sine wave rather than a changeable DC variable, the baseband LPF will
produce a filtered sine wave as output. The LPF suppresses high frequency components over its cutoff
frequency, allowing only lower frequency components of the sine wave to get through. The output will
remain a sine wave, but its amplitude and frequency will be restricted by the LPF's properties.

Question 8
What does the FM modulator’s output signal tell you about the ZCD signal’s duty cycle?
The output signal from the FM modulator reveals the duty cycle of the zero crossing detector signal. The
frequency variations of the FM modulated signal are converted into shifts in the duty cycle of the ZCD
signal via frequency modulation. The ZCD signal has a rectangular waveform, and its duty period is the
ratio of total time in the high state to total time in the signal. We can discover matching oscillations in the
ZCD's duty cycle by evaluating the FM modulator's output signal, which helps us comprehend the
frequency variations of the modulated signals.