Data Interpretation 2.docx

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Data Interpretation:

Step 3:

Ch1 shows the amplitude of the message measuring a 4Vp-p while Ch3 shows thecarrier signal measuring also a 4Vp-p. This was measured at the inputs of the MultiplierModule. We’ve noticed from the graph that which means the frequency ofthe carrier is much greater than that of the frequency of the message. This only showsthe relationship of the message and the carrier before they are inputted at the multiplier.



Step 6:

This picture shows the 4Vp-p output at the multiplier.

From this equation:

cost . cost = (E/2) cos t + (E/2) cos( )t

It shows that the product is represented by two new signals, one on the sum frequency

, and one on the difference frequency ) as shown in the figure below. This

equation shows that the component at frequency ( ) contains exactly the same

information as the component at ) since one can be uniquely determined from the

other by taking the complex conjugate. The portion of the spectrum for || > is called

the upper sideband and the portion for|| < is called the lower sideband. The fact thatthe modulated signal contains both portions of the spectrum explains why the term,double-sideband, is used.



Remembering the inequality the two new components are located closeto the frequency w rad/s, one just below, and the other just above it. These arereferred to as the lower and upper sidebands respectively.

These two components were derived from a ‘carrier’ term on rad/s, and a message on

rad/s. Because there is no term at carrier frequency in the product signal it isdescribed as a double sideband suppressed carrier (DSBSC) signal.

The term ‘carrier’ comes from the context of ‘double sideband Amplitude Modulation'(commonly abbreviated to just AM).

Step 7:



This shows picture similar to that of figure 2 (showing the message and the output of the

multiplier). A multiplier is a device that performs the multiplication of signals is often

called a product modulator or balanced mixer. The output is consists of a message signal

combined with the frequency carrier. The equation below shows how to compute for the

output given a message or audio and a carrier signals.



This figure below shows a diagram on what does a mixer or multiplier do with our input

signals.

http://en.wikipedia.org/wiki/File:DSBSC_Modulation.svg



Step 8:

This was the maximum amplitude before the overloading occurs. The message signal is

measured still at 4Vp-p at Ch1 and the output of the multiplier at Ch3. Importantly,

notice that two of the products are sinewaves at the message frequency. In other words,

the message has been recovered. As the two message signals are in phase, they simply

add together to make one larger message. Notice also that two of the products are non-

message sinewaves. These sinewaves are unwanted and so a low-pass filter is used to

reject them while keeping the message.



This was the output after the overloading. The amplitude of the message is still the

same. The carrier signal is the one that was varied making the output signal

clipped at certain amplitude therefore varying the carrier signal’s amplitude might

cause overloading of the output signal so we should be aware of the maximum

amplitude of our carrier signal before it overloads our output.

Step 18:

After getting the frequency at the FREQUENCY COUNTER,

f=2643.5kHZ

f/360 = 7.34kHz therefore we didn’t able to produce a frequency over 10kHz which was

needed in this certain step.

Step 21: We’ve tried to determine the Upper edge of the DSBC by observing the

DSBSC while adjusting the filter passband edge giving us:

fA=1021.629



Step 22: Lowering the filter passband edge until the sine wave just starts to reduce

gives us:

fB=879.759kHz

Step 23: Lowering the filter passbandedge much further just so enough to cancel out

our output gives us:

fC=620.515kHz

We’ve researched about what goes wrong at step 18 and why it doesn’t exceed the

10kHz just like what the experiment told us to do.

This is what we must do:

Adjust the VCO frequency to 10 KHz. Set the Audio Oscillator to about 2 KHz. Confirm that the

output from the Multiplier looks like Figure 2. We failed analyze adjusting the input frequency

from the Audi from 1kHz to 2 kHz and increasing the VCO frequency to 10kHz will give us the

correct frequency thus making the succeeding steps correct.

Data Interpretation 2.docx

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