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Pi Pico Rx
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Pi Pico Rx is a minimal SDR reciever based around the Raspbery Pi Pico. The design uses a "Tayloe" Quadrature Sampling Detector (QSD) popularised by Dan Tayloe. And used in many HF SDR radio designs. This simple, design allows a high quality mixer to be implemented using an inexpensive analogue switch.
A quadradure oscillator is generated using the PIO feature of the RP2040. This eliminaes the need to use an external programable oscillator. Without overclocking the device this supports frequencies up to about 30MHz, conveniently covering the LW, MW and SW bands.
The IQ output from the QSD is amplified using a high-speed, low-noise op-amp. The I and Q channels are sampled by the built-in ADC which provides 250kHz of bandwidth. The dual core ARM Cortex M0 processor implements the Digital Signal Processessing algorithms, demodulating AM, FM, SSB and CW to produce an audio output.
Audio output is provided using a PWM followed by a low-pass filter.