Which mode is normally used when sending RTTY signals via AFSK with an SSB transmitter?

When operating Radio Teletype (RTTY) using Audio Frequency Shift Keying (AFSK) via a Single Sideband (SSB) transmitter, the long-standing convention is to use Lower Sideband (LSB). This applies across all HF bands, even on bands like 20 meters where Upper Sideband (USB) is the standard for voice communications. Using LSB for AFSK RTTY ensures that the transmitted mark and space tones maintain the correct frequency relationship (polarity). If one station uses LSB and the other uses USB, the tones will be inverted, and the receiving software will print gibberish. While many modern digital modes like FT8 or PSK31 standardize on USB for all bands, traditional AFSK RTTY remains the notable exception where LSB is the norm.