Each of the parameters depends on C/N and also on the modulation technique. That gets us into analogue and

digital modulations. There are three types for each of the two kinds of modulation. First we looked at analogue modulation.

the baseband signal. The output is the modulated carrier. We assumed for the carrier a cos wave and for the baseband signal also a cos wave, however at a much lower frequency. We wrote down the equations for AM, FM and PM.

We plotted the amplitude modulated carrier and imagined how it would change if we changed the modulation index.

We plotted the spectrum of the baseband signal and the AM carrier. For the general case of a continuum of a spectrum, we use the symbolic triangle for the spectrum. We learned about upper side band (USB) and lower side band (LSB). We also learned that AM does not provide an improvement of the S/N in comparison to the C/N. Basically the highest S/N for amplitude modulation cannot be larger than C/N. Then we turned to FM. We plotted the the amplitude as a function of time for a simple cases of a FM modulated carrier and looked at the equation for a frequency modulated carrier. Bessel functions were needed.

Here is a graphical comparison between AM and FM.

For the FM spectrum, click here. For an explanation and for applets for analog modulation (AM and FM) click here.

Although the theoretical bandwidth of an FM waveform is infinite, Carson's rule gives a bandwidth where most of the information is contained. We looked at examples. We looked at the improvement factors.

1 December 2017

for analogue modulation. We looked at the whole scheme of a transmitting and receiving end of a typical TDM system. TDM stands for time-division-multiplexing.