4.6. Digital modulation
The signal consisting of the product of the data and the code is to be transmitted from the satellite to the user. However, it cannot be sent in this binary baseband form, for two key reasons. First, the transmitting antenna needs to be of the order of the wavelength of the signal being transmitted for efficient transmission. The encoded data, which are mostly concentrated within the low frequency ranges and hence have very high wavelength, would require a very large transmitting antenna for the purpose. Second, the channel through which the signal passes cannot efficiently propagate the DC components and acts as a bandpass filter. This signal is ridden on a carrier wave of suitable high frequency. The technique of the ...
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