What is indicated on a waterfall display by one or more vertical lines on either side of a data mode or RTTY signal?
Why A clean FSK or PSK data signal shows only its intended tones on a waterfall. When the audio drive into an SSB transmitter is too high, the final amplifier is driven into nonlinearity and intermodulation products appear as extra tones spaced on either side of the wanted signal, drawing as additional vertical lines. The cure is to reduce the soundcard or microphone gain and the ALC action until those extra lines disappear.
Watch out Insufficient modulation is tempting because it is the opposite fault, but too little drive simply makes the trace faint or absent; it never adds spurious tones. Long path and backscatter are propagation effects that may smear or echo a signal, not create symmetric sidebands.
Extra lines means extra drive: turn the audio down until the sidebands vanish.