Question

how to calculate frequencies

Asked by: Rafi-muqaddar

Hi
I wonder if anybody could help me. I have got a question with 4 parts.

Q.A 75MHz carrier having an amplidtude of 50 v is modulated by a 3 KHz Audio signal having an amplitude of 20 v

1.what would be the modulation factor and percent modulation
2.What would be the trignometric equations for carrier and modulating waves
3.what frequencies will show up in the spectrum analysis of the modulated wave
4.If the total power content of this system is 1Kw.determine the power at the carrier frequency and at each side

Please provide me with the formulas for my understanding
thanks
Rafi-muqaddar

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Asked On
2006-01-05 at 13:59:35ID21685787
Tags

calculate

,

frequencies

,

how

,

modulation

Topic

Math & Science

Participating Experts
1
Points
500
Comments
4

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Answers

 

by: ozoPosted on 2006-01-05 at 14:21:46ID: 15623711

You have not specified the functional form of the modulation to be used.
Just saying amplitude modulation (which you don't specify in this question) is not enough,
since that could still cover things like
output = carrier * signal/20v
or
output = carrier * (1+signal/20v)
or other more complicated variants.
your reference to "each side" suggests that you might not be talking about a supressed sideband modulation, but that still leaves a lot of ambiguity about exactly how you are doing
the modulation.

 

by: ozoPosted on 2006-01-05 at 15:26:26ID: 15624466

If, judging from your other questions, you are trying to say that the output is
carrier * (50v + signal*20v) then that is the same as the sum of three frequencies
50v*carrier + 20v*(sideband at carrier frequency+signal frequency) + 20v*(sideband at carrier frequency-signal frequency)
I think the rest of this was covered in another question which really seems to be the same question, and since the maximum numner of points per question is 500 (http:/help.jsp#hi50) you probably should ask customer support to combine the two.

 

by: Rafi-muqaddarPosted on 2006-01-05 at 15:59:50ID: 15624747

Hi
Thanks all those who replied.Could any body give me the answer of part 1. and part 4. I have done the other ones.
Thanks
Rafi-muqaddar

 

by: ozoPosted on 2006-01-05 at 17:19:53ID: 15625296

the depth of modulation would be just 20/50
If there are two sidebands the power of the carrier and the sidebands would be in the ratio
50^2, (20/2)^2, (20/2)^2
 
when I said
50v*carrier + 20v*(sideband at carrier frequency+signal frequency) + 20v*(sideband at carrier frequency-signal frequency)
I should have said 50v*carrier + 20v*(sideband at carrier frequency+signal frequency)/2 + 20v*(sideband at carrier frequency-signal frequency)/2

20120131-EE-VQP-002

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