Why do most amateur stations use lower sideband on the 160-, 75-, and 40-meter bands?
Lower sideband is more efficient than upper sideband at these frequencies
Lower sideband is the only sideband legal on these frequency bands
Because it is fully compatible with an AM detector
It is commonly accepted amateur practice✓Correct answer
Explanation
Neither sideband has any technical advantage at these frequencies and the FCC specifies no sideband on them, so the 10 MHz split is pure custom inherited from early sideband equipment. It survives only because everyone follows it.