Modulation is the process of superimposing an audio signal on a high frequency wave, some characteristics of which varies as a function of instantaneous value of audio signal.

Two uses of geostationary satellites:

(a) Communication through telephones, internet etc.

(b) Long distance transmission of television programmes.

Remote sensing earth’s surface, by means of observations from fixed point like towers, balloons, aeroplates, polar satellites, geostationary satellites or space stations.

Analog signal has infinite number of values or many continuously varying values whereas digital signal has only two values.
Analog signal gives a sinusoidal wave and Digital signal gives a rectangular wave or square pulse.