Amplitude modulation
What is AM?
Amplitude Modulation is the done by modulating the Amplitude of an sinoid Carrier signal using the incoming signal.
The Carrier signal is a sinusoid with a fixed Frequency at least twice as high as the highest frequency occuring in the spectrum of the incoming signal. Usually a much higher frequency is choosen.
Amplitude Modulation schemes have been widely used in Analog Radio.
Mathematical Setting
The output signal is the simple product of incoming signal and Carrier Signal with frequency f:
output(t) = input(t) * sin(f * t)
TODO: it would be nice to type formulas in TeX, is this working in this wiki?
- Sure. But some prerequisites has to be met. Perhaps ist easier to use pictures of the formula (the manual way of what the wiki does).
An Example
 Carrier Signal in time domain |
File:AM picture4.jpg Carrier Signal in frequency domain (to be added) |
 Modulating Signal in time domain |
File:AM picture5.jpg Modulating Signal in frequency domain (to be added) |
 AM Signal |
File:AM picture6.jpg AM Signal in frequency domain (to be added) |
Special Kinds of AM
- DSSC, Double Sideband Supressed Carrier
- SSB, Single Side Band
- Residual Sideband Modulation (modulation used for analog TV applications)
- QAM, Quadrature Amplitude Modulation
Aquired Bandwidth
it would be nice to have a picture showing how AM signals in the frequency spectrum behave and how much bandwidth they allocate. A short overview of AM-related problems would be nice, too. Has anybody of you this info handy?
what about noise sensitivity?