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Amplitude Modulated Waveform

Using the given graph I was asked to sketch the variation of VOltage with time.

Is the graph correct ?

IMG_0190.jpgImage.jpg
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Yes it's correct.
They're difficult to hand draw.
(edited 12 years ago)
Original post by Stonebridge
Yes it's correct.
They're difficult to hand draw.


Could you help me with this question, please ?

Question 15 (b) (i)
Original post by Ari Ben Canaan
Could you help me with this question, please ?

Question 15 (b) (i)


Have you studied the theory for this topic?
It's a standard simple calculation with AM if you are given the frequency range of the broadcast music, to then say what the bandwidth is.
http://hyperphysics.phy-astr.gsu.edu/hbase/audio/sumdif.html#c3
Original post by Stonebridge
Have you studied the theory for this topic?
It's a standard simple calculation with AM if you are given the frequency range of the broadcast music, to then say what the bandwidth is.
http://hyperphysics.phy-astr.gsu.edu/hbase/audio/sumdif.html#c3


I have studied the topic but I was confused as to whether to consider the 30 Hz or 4500 Hz frequency in the information signal.

Having read the above link I see that bandwith is twice the highest frequency in the signal.

I assume it is the information signal they're talking about ?

Also why do we double the highest frequency ? Why not the lowest ?
Original post by Ari Ben Canaan
I have studied the topic but I was confused as to whether to consider the 30 Hz or 4500 Hz frequency in the information signal.

Having read the above link I see that bandwith is twice the highest frequency in the signal.

I assume it is the information signal they're talking about ?

Also why do we double the highest frequency ? Why not the lowest ?


It's because the carrier wave frequency fc and the modulation wave frequency fm interact such that the resultant wave has sidebands with a frequency of fc + fm and fc - fm (as explained in the link)
The bandwidth is the maximum range of frequency above and below the carrier.
You get this by using the maximum frequency of the modulation (signal), not the minimum.
Original post by Stonebridge
It's because the carrier wave frequency fc and the modulation wave frequency fm interact such that the resultant wave has sidebands with a frequency of fc + fm and fc - fm (as explained in the link)
The bandwidth is the maximum range of frequency above and below the carrier.
You get this by using the maximum frequency of the modulation (signal), not the minimum.


I apologise from bringing this up again but could you tell me what the graph on page 19 would look like (post #5)?

How do we determine the carrier frequency ? And what would the frequency of the sidebands be ?
The graph is only a "sketch".
It looks something like this (on the right in the link)
http://en.wikipedia.org/wiki/Sideband
You just choose a carrier frequency in the range given in the question as a typical example.
Then calculate the sidebands according to the standard formula using the carrier frequency you have chosen as an example and modulation frequencies given.

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