-Last step of this sequence on the formation of the signal. We previously saw that the role of the modulator within the transmitter was to build a signal adapted to the propagation channel to be crossed. First, it will build it according to the available bandwidth in the channel. Then, it has to transport the spectrum of the generated signal in the band it has been allocated within the propagation channel. For this kind of transmission, we talk about a carrier frequency transmission because we use a carrier wave which carries the message in the allocated band. It will carry it in one of its parameters: amplitude, phase, frequency. This wave is sinusoidal and its frequency is called the carrier frequency. It corresponds to the central frequency of the allocated band in the propagation channel. Let us get back to the FM radio example. I kept the France Info example with a central frequency of 105.5 MHz and a certain band available around it. When it builds its signal, France Info creates a signal with a band used that is compatible with the available band that has been reserved in the propagation channel and corresponding to FM broadcasting. Once this is done, this spectrum needs to be carried in the band allocated to France Info. We talk about carrier frequency transmission and for this purpose we use this sinusoidal wave called a carrier wave. It is not always mandatory to perform a carrier frequency transmission. For example, in the case of a transmission between two computers using a cable, the propagation channel is dedicated so the signal does not need to be transported in a certain allocated band. In that case, we keep the signal within a low-frequency spectrum. All signals are generated within a low-frequency spectrum. Then we carry them in the allocated band or not. When we do not carry the signal spectrum in the allocated band, we talk about a baseband transmission. Regarding satellite transmissions, the space used to transmit is the free space. Of course, we will always perform a carrier frequency transmission. We will see it later on. We always have an allocated frequency space. We have to first generate the signal with a low-frequency spectrum, then transport this spectrum in the band that was reserved for us.