*Question T8A01:
Which of the following is a form of amplitude modulation?*  

*Correct Answer is  C: Single sideband*  

### AI Response: (may contain errors)  

Amplitude modulation (AM) is a technique used to encode information in a carrier wave by varying its amplitude. Let's break down the question and the choices:

### Correct Answer: C: Single sideband (SSB)

- **Why it's correct**: 
  - Single sideband is a form of amplitude modulation where only one of the sidebands (either the upper or lower) is transmitted, and the carrier is suppressed. This makes SSB more efficient in terms of bandwidth and power compared to standard AM, which transmits both sidebands and the carrier.

### Why the other choices are incorrect:

- **A: Spread spectrum**: 
  - Spread spectrum is a technique used to spread the signal over a wider bandwidth than the minimum required. It is not a form of amplitude modulation; instead, it often uses techniques like frequency hopping or direct sequence spread spectrum.

- **B: Packet radio**: 
  - Packet radio refers to a method of digital communication where data is sent in packets. It does not involve amplitude modulation; rather, it typically uses digital modulation techniques like PSK or FSK (Frequency Shift Keying).

- **D: Phase shift keying (PSK)**: 
  - PSK is a digital modulation technique that conveys data by changing the phase of the carrier wave. It does not involve varying the amplitude of the signal, which is a key characteristic of amplitude modulation.

### Summary:
- **Single sideband (SSB)** is a form of amplitude modulation.
- **Spread spectrum**, **packet radio**, and **phase shift keying (PSK)** are not forms of amplitude modulation.

This understanding of modulation types is crucial for the Extra Class exam, as it helps differentiate between various communication methods used in amateur radio.