A transmitter upconverts a SSB data signal during a first operational mode using a RF upconverting signal having a frequency that is offset from a center frequency of a channel (.omega..sub.C) by an amount that depends on the data signal's SSB bandwidth (.omega..sub.M). In a second operational mode, the transmitter upconverts a tone signal having a frequency .omega..sub.M using the same RF upconverting signal. The upconverted tone signal can be used as a continuous wave (CW) carrier signal having a frequency .omega..sub.C. The transmitter has a single RF oscillator to output both a SSB signal centered at frequency .omega..sub.C during the first mode and a carrier signal of frequency .omega..sub.C during the second mode.