What audio frequencies are used in a two-tone test of the linearity of a single-sideband phone transmitter?

For a two-tone linearity test to be effective, the chosen audio tones must first fall within the transmitter's audio passband. For standard SSB communications, this passband is typically between 300 Hz and 3000 Hz. Tones like 20 Hz or 20 kHz (as suggested in one distractor) would be completely blocked by the transmitter's audio filters. Furthermore, the two tones must not be harmonically related. A harmonic relationship means one frequency is a direct integer multiple of the other (for instance, 1200 Hz and 2400 Hz). Using harmonics masks the intermodulation distortion products because they will overlap mathematically, rendering the visual test results ambiguous. Therefore, any two non-harmonically related tones within the audio passband (such as 700 Hz and 1900 Hz) are acceptable. This ensures both tones successfully pass through the transmitter's filters and interact to create a clear, measurable intermodulation pattern.