# Amplitude and frequency modulation help

Watch
Announcements
#1
https://isaacphysics.org/questions/a...6-54bcfc067f3e

Disclaimer: I’ve not studied this I’m doing it as extra work on my own

Got part a no problems
B) why is it not 11000 (10000) as read off graph
C) I’ve spilt it to
Cos(2πfct) + 1/4cos(2πt(fs+fc))+ 1/4cos(2πt(fs-fc))
So then I square each one set the sum = 0.7 and find the biggest one but what’s the max frequency? Surely I’ve got too many unknowns
0
7 months ago
#2
(Original post by Sophhhowa)
B) why is it not 11000 (10000) as read off graph
What period do you read off the graph to get this?
0
7 months ago
#3
(Original post by Sophhhowa)
C) I’ve spilt it to
Cos(2πfct) + 1/4cos(2πt(fs+fc))+ 1/4cos(2πt(fs-fc))
So then I square each one set the sum = 0.7 and find the biggest one but what’s the max frequency? Surely I’ve got too many unknowns
Firstly, note that it is not the square of each term you want, it is the square of their amplitudes. The equation you end up with only have one unknown constant, which is the constant of proportionality between the sum of the squares of these amplitudes and the 0.7.

As for which is the maximum frequency - the frequencies of those three terms are fc, fc + fs and fc - fs, so one of them is clearly larger than the other two.
1
#4
(Original post by Pangol)
What period do you read off the graph to get this?
I was looking at the wrong wave (whoops) got it now
0
#5
(Original post by Pangol)
Firstly, note that it is not the square of each term you want, it is the square of their amplitudes. The equation you end up with only have one unknown constant, which is the constant of proportionality between the sum of the squares of these amplitudes and the 0.7.

As for which is the maximum frequency - the frequencies of those three terms are fc, fc + fs and fc - fs, so one of them is clearly larger than the other two.
Thank you so much. Got it now. I think I just panicked coz I’d never seen anything like this before.
0
X

new posts
Back
to top
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### Poll

Join the discussion

#### Should there be a new university admissions system that ditches predicted grades?

No, I think predicted grades should still be used to make offers (706)
33.93%
Yes, I like the idea of applying to uni after I received my grades (PQA) (889)
42.72%
Yes, I like the idea of receiving offers only after I receive my grades (PQO) (393)
18.89%
I think there is a better option than the ones suggested (let us know in the thread!) (93)
4.47%