LSB and USB refer to what in radio communications?

• A. Modulation methods
• B. Sideband types
• C. Power levels
• D. Filters

Answer: (B)

LSB and USB indicate which sideband carries the information in a radio signal. They are sideband types from single-sideband modulation. When you modulate a carrier with audio, you create an upper sideband above the carrier and a lower sideband below it. In single-sideband, the carrier is suppressed and only one of those sidebands is transmitted, so the signal uses only one half of the spectrum. The choice between upper or lower sideband is largely historical and band-dependent, but the key idea is that these terms name the sideband that actually carries the information, not a modulation method, power level, or filter.