In a single-sideband transmitter, which stage transposes the single-sideband signal to the operating frequency?

In radio architecture, a mixer is a non-linear circuit that combines two input frequencies to produce sum and difference frequencies at its output. This is the process known as heterodyning. In a single-sideband transmitter, the mixer takes the fixed intermediate frequency (IF) SSB signal and combines it with the variable signal from the Variable Frequency Oscillator (VFO). This process transposes, or translates, the SSB signal from the fixed IF up to the desired final operating frequency. While the balanced modulator initially creates the sidebands and the VFO provides the tuning reference frequency, it is the mixer that actually performs the frequency shift necessary for transmission.