What is the primary function of the power amplifier in a CW transmitter?

The primary function of the power amplifier in a Continuous Wave (CW) transmitter is to increase the power level of the signal. In a CW transmission system, the power amplifier takes the relatively low-level audio or intermediate frequency (IF) signal and boosts it to a sufficient level so that it can effectively drive the antenna for transmission.

Increasing the power level is critical because it enhances the signal's range, allowing it to reach distant receiving stations with sufficient strength. Without the power amplifier, the weaker signal would not be able to travel far enough to be reliably received due to losses in the transmission medium and the sensitivity limitations of the receiving equipment.

In terms of the other functions presented in the options, modulation is not performed by the power amplifier; instead, it is handled by earlier stages of the transmitter. The generation of the carrier frequency occurs in oscillators, which is distinct from amplification. Filtering is typically done in separate stages to clean up the signal before amplification and ensure that only the desired frequencies are transmitted. Thus, while these processes are essential in the context of a transmitter, they are distinct from the role of the power amplifier itself.