Hello all, suppose we have a signal Acos(2pi f t )
power = (A/sqrt2)^2 = A^2 / 2
If we represent the same on a spectrum diagram , we get 2 bands, one at negative f and one at positive f with half the amplitude.
power = sum of power in each bands = (0.5A/sqrt2)^2 * 2 = A^2 /4
why the powers of part 1 and 2 not equal ?

 

Hello,

Read this page:
http://www.radio-electronics.com/in.../am-amplitude-modulation/theory-equations.php

Bertus

 

Hello,

Read this page:
http://www.radio-electronics.com/in.../am-amplitude-modulation/theory-equations.php

Bertus

Hello thanks for the link , but there it discusses about 100% modulation and the sidebands have 1/4 the power of the carrier. However my question was , ' if the signal is drawn on a frequency spectrum , we'll get 2 bands with half amplitude. Adding the power of both bands together does not equal the power calculated normally ' why ?

 

Hello,

Do you mean AM with a suppressed carrier?
https://en.wikipedia.org/wiki/Double-sideband_suppressed-carrier_transmission

Bertus

 

I think you are misinterpreting the power spectrum.
Half of the power will be in each sideband, not half the signal amplitude.

The signal is in real time space, no negative time.
The power spectrum is in positive and negative frequencies.

 

Hello,

Do you mean AM with a suppressed carrier?
https://en.wikipedia.org/wiki/Double-sideband_suppressed-carrier_transmission

Bertus

No, in the frequency spectrum, we have a mirror image of the sidebands , if you sum the powers of the sidebands for negative frequencies and the positive ones, you don't get the same answer as you would '

 

I think you are misinterpreting the power spectrum.
Half of the power will be in each sideband, not half the signal amplitude.

The signal is in real time space, no negative time.
The power spectrum is in positive and negative frequencies.

Hello friend, really I'm confused about that. Will really help if I could get a more detailed explanation please. I know power depends on amplitude and negative frequency means rotating in the opposite direction , why the sum of powers not equal in both my calculations ?

 

Why do you say there is half the amplitude in the sidebands?
Work backwards. If the power in the sideband is half the total power, what would be the amplitude?