Question T8A03
From subelement T8 - T8A
Which type of voice mode is often used for long-distance (weak signal) contacts on the VHF and UHF bands?
Why is this correct?
SSB (Single Sideband) is correct because it's more energy-efficient than FM, making it ideal for weak signal work on VHF/UHF. SSB uses only about 3 kHz bandwidth compared to FM's 10-15 kHz, concentrating power into a narrower signal. FM works well for local repeater communications but lacks the efficiency needed for long-distance contacts where signals are weak. DRM and PM aren't typically used for this purpose.
Memory tip
Remember the efficiency principle: narrow bandwidth modes concentrate power better for weak signals. When you see 'weak signal' or 'long-distance' on VHF/UHF, think SSB. FM dominates local VHF/UHF communications, but SSB takes over when you need maximum efficiency to punch through at distance.
Learn more
SSB's narrow 3 kHz bandwidth versus FM's 10-15 kHz bandwidth demonstrates a fundamental amateur radio principle: frequency privileges must be used efficiently. In weak signal work, operators need every decibel of effective radiated power. SSB's elimination of the carrier and one sideband means all transmitted power carries information, unlike FM where significant power goes into the carrier. This efficiency becomes critical during VHF/UHF contests, EME (moonbounce), and other challenging propagation conditions.
Think about it
Why do you think amateur radio operators don't simply use higher power FM instead of switching to SSB for weak signal work on VHF and UHF?