Ham Radio General Class Practice Test

What is the name of the process that changes the envelope of an RF wave to carry information?

1. Phase modulation

2. Frequency modulation

3. Spread spectrum modulation

4. Amplitude modulation

The correct answer is: Amplitude modulation

The process that changes the envelope of an RF wave to carry information is called Amplitude Modulation (AM). In amplitude modulation, the amplitude (or voltage level) of the carrier wave is varied in relation to the amplitude of the information signal, such as audio or video data. This means that as the information signal changes, so does the height of the RF wave, effectively embedding the information within the carrier wave. This method is widely used in various communication applications because it allows for easy demodulation at the receiver end. Radiocommunications such as AM radio broadcasting utilize this technique to transmit audio signals, with the amplitude variations corresponding to the sound waves being broadcast. While phase modulation and frequency modulation are also methods of conveying information through RF waves, they do so by altering different characteristics of the carrier wave — phase and frequency, respectively — rather than the envelope itself. Spread spectrum modulation involves spreading the signal over a wider bandwidth and is primarily used for its resistance to interference and improved security. Each of these serves a specific purpose in communications technology, but only amplitude modulation directly involves modifying the envelope of the RF signal.