Pure Carrier vs. Modulated Carrier: Understanding the Difference

This article explains the difference between a pure carrier (unmodulated carrier) and a modulated carrier.

The figure below shows an extracted part of the common physical layer modules of a typical wireless modem.

Figure mentions two cases:

In Case-1, as shown in the figure, if all 1’s or 0’s or alternate ones and zeros are fed, which is a known standard pattern, this results in a pure carrier, i.e., an unmodulated carrier. This happens because the phase of the modulated carrier does not change.

Figure 2 shows a pure carrier in the middle on top of the modulated spectrum.

As mentioned in Case-2, when a PN sequence is fed to the modem, it leads to a modulated carrier as the output, as shown in the figure.