A power amplifier subsystem, comprising: a first channel circuit, comprising: a first channel supply path configured to process a first channel input signal to produce a first channel variable voltage based on the first channel input signal; a first channel gain path configured to process the first channel input signal to produce a first channel gain control signal; and a first channel variable gain amplifier configured to: receive the first channel variable voltage; receive the first channel gain control signal; and amplify a local oscillator signal such that, during operation, the first channel variable voltage is applied as a supply voltage to the first channel variable gain amplifier, a gain of the first channel variable gain amplifier being modulated by the first channel gain control signal to modulate the local oscillator signal and to produce a modulated radio signal; characterized in that the first channel variable voltage produced by the first channel supply path is a non-constant function of the first channel input signal if the first channel input signal exceeds a threshold and is a constant if the first channel input signal is below the threshold; and the first channel gain control signal produced by the first channel gain path is a constant if the first channel input signal exceeds the threshold and is a non-constant function of the first channel input signal if the first channel input signal is below the threshold. a first channel circuit, comprising: a first channel supply path configured to process a first channel input signal to produce a first channel variable voltage based on the first channel input signal; a first channel gain path configured to process the first channel input signal to produce a first channel gain control signal; and a first channel variable gain amplifier configured to: receive the first channel variable voltage; receive the first channel gain control signal; and amplify a local oscillator signal such that, during operation, the first channel variable voltage is applied as a supply voltage to the first channel variable gain amplifier, a gain of the first channel variable gain amplifier being modulated by the first channel gain control signal to modulate the local oscillator signal and to produce a modulated radio signal; characterized in that a first channel supply path configured to process a first channel input signal to produce a first channel variable voltage based on the first channel input signal; a first channel gain path configured to process the first channel input signal to produce a first channel gain control signal; and a first channel variable gain amplifier configured to: receive the first channel variable voltage; receive the first channel gain control signal; and receive the first channel variable voltage; receive the first channel gain control signal; and the first channel variable voltage produced by the first channel supply path is a non-constant function of the first channel input signal if the first channel input signal exceeds a threshold and is a constant if the first channel input signal is below the threshold; and the first channel gain control signal produced by the first channel gain path is a constant if the first channel input signal exceeds the threshold and is a non-constant function of the first channel input signal if the first channel input signal is below the threshold.