Final answer:
The mixer stage of a superheterodyne receiver lies between the RF amplifier stage (tuneable stage) and the IF amplifier stage (fixed tuned stage). It plays a crucial role in converting the incoming RF signal into an IF signal for further processing.
Step-by-step explanation:
The stage of a superheterodyne receiver that lies between a tuneable stage and a fixed tuned stage is the mixer stage. In a superheterodyne receiver, the received signal is first passed through the RF (radio frequency) amplifier stage and then sent to the mixer stage. The mixer stage combines the incoming RF signal with a local oscillator signal to produce an IF (intermediate frequency) signal. This IF signal is then amplified by the IF amplifier stage, which is a fixed tuned stage. The purpose of the IF stage is to amplify the desired signal while suppressing the unwanted frequencies before demodulation. Finally, the demodulated signal goes through the audio amplifier stage, which amplifies the signal enough to drive a speaker or to be recorded.