SDR equivalents to analog functions in a small-scale radio telescope

The signal arrives from the antenna, and is amplified by one or more stages of RF amplification (and sometimes bandpass filterig), and is then presented to the 1 mixer where the signal is converted to a fixed intermediate frequency by the mixing action between the incoming signal frequency and the frequency produced by the Variable Frequency Oscillator. The result is a fixed intermediate frequency that is filtered, and amplified by the 1 IF amplifier. The signal is then typically mixed again in the 2 mixer stage, and converted to the final intermediate frequency with a fixed Local Oscillator. Once the final IF is produced, it is detected with a square-law detector, usually a detector diode. The detector produces an output voltage that is proportional to the incident AC power. This voltage is then amplified by the DC amplifier, and low-pass filtered with an integrator stage. The output of the integrator is then usually fed to a recording device of some sort.