The transmitted message gets attenuated in propagating through the channel. The receiving antenna is therefore to be followed by an amplifier and a detector. In addition, to facilitate further processing, the carrier frequency is usually changed to a lower frequency by what is called an intermediate frequency(IF) stage preceding the detection . Hence, Statement 2 is correct. The detected signal may not be strong enough to be made use of and hence is required to be amplified. Detection is the process of recovering the modulating signal from the modulated carrier wave. Hence, Statement 1 is correct. The modulated signal of form is passed through a rectifier to produce the output. The envelope of a signal is the message signal. In order to retrieve m(t), the signal is passed through an envelope detector (which may consist of a simple RC circuit) . There is one specific type of analog modulation namely Amplitude Modulation (AM). Other forms of modulation and digital communication systems play an important role in modern communication. These and other exciting developments are taking place every day. So far we have restricted our discussion to some basic communication systems.
