*Question G2A05:
Which mode of voice communication is most commonly used on the HF amateur bands?*  

*Correct Answer is  C: Single sideband*  

### AI Response: (may contain errors)  

The correct answer is **Single sideband (SSB)**.

1. **Why the correct answer is correct:**
   - Single sideband (SSB) is the most commonly used mode of voice communication on the HF amateur bands because it is more efficient in terms of bandwidth and power usage compared to other modes. SSB is a form of amplitude modulation (AM) that eliminates one of the sidebands and the carrier, which reduces the bandwidth by half and concentrates the power into a single sideband, making it more effective for long-distance communication.

2. **Why the other choices are incorrect:**
   - **Frequency modulation (FM):** FM is not commonly used on HF bands because it requires a wider bandwidth than SSB. FM is more commonly used on VHF and UHF bands where bandwidth is less of a concern.
   - **Double sideband (DSB):** DSB transmits both sidebands and the carrier, which uses more bandwidth and power than SSB. It is less efficient and therefore not commonly used on HF bands.
   - **Single phase modulation:** This is not a standard mode of voice communication in amateur radio. It is not used on HF bands for voice communication.

3. **Useful formulas or rules of thumb:**
   - SSB is a type of AM where only one sideband is transmitted, either the upper sideband (USB) or the lower sideband (LSB).
   - Bandwidth for SSB is approximately half that of AM, typically around 2.5 to 3 kHz, compared to 6 kHz for full AM.

Understanding these points will help you recognize why SSB is the preferred mode for voice communication on HF bands.