In the last instalment (Part 3) of my STEMlab Red Pitaya SDR transceiver project, I covered the process of moving some of the control logic off the Red Pitaya and onto the controller module I designed around an STM32 “Blue Pill” microcontroller. This shift has given me far more reliable handling of RX/TX transitions, cleaner timing, and full control over the PE4302 attenuation stages—something the SDR software alone couldn’t provide. The effort that went into designing the controller and writing the firmware is now paying dividends, as the module has become the central piece that ties the hardware together and keeps the system predictable while I continue developing the rest of the transceiver. With the receive path behaving exactly as intended, the controller is now ready to support the next phase of the build as I move toward completing the transmit chain and integrating PureSignal.
As the build progresses, I’m really starting to appreciate the benefits of the new features being added. The digital attenuator in the receive path has already proven its worth, especially when strong nearby signals or a barrage of contest stations threaten to overload the ADC. Automatic switching of the RF preamplifier on the higher bands has also become a welcome addition, bringing weaker signals up out of the noise without me having to remember to enable it manually. These refinements make the receive chain far more robust and user‑friendly as the project continues to evolve.
In this blog post, I explore the role of audio codecs in my transceiver build, specifically how they convert analogue microphone signals into digital data for transmission, and then back into analogue audio for clean, low latency monitoring and listening. This marks an important step toward completing the audio path and integrating full voice capability into the SDR architecture.
