SDR Transceiver Teensy 4.1, Transmit and Receive Audio Board

This board contains the Teensy 4.1, SGTL5000 transmit codec, PCM1808 & PCM5102 receive ADC and DAC, respectively, and the audio chain providing speaker and Line Out audio. On the transmit side, the board takes Line In audio and produces quadrature audio output for the transmitter Quadrature Sampling Exciter (QSE), and on the receive side takes 48-KHz quadrature receiver IF from the Quadrature Sampling Detector (QSD) and produces audio output.

The receiver audio chain circuitry is the same as that used in the 2020 Transceiver.

I extracted the core DSP transmit and receive routines from Jack and Al’s code, and refactored the code into a single file with function calls to access DSP functions from my main transceiver code. I initially got the existing transceiver code running on the Teensy, then the DSP transmit code, and finally the DSP receive code.

The biggest challenge with this board was hand soldering the SGTL5000 in a QFN-20 package. I succeeded on my second attempt by first hand soldering the 20 contacts, and then soldering the concealed ground pad using vias from the backside of the board. In hindsight, a way to avoid this would be to use a second PCM1808/PCM5102 pair on the transmit side rather than the SGTL5000.

Teensy 4.1, Transmit and Receive Audio Board plugged into the Backplane Board.

In the picture above, the SGTL5000 is in the upper left of the board, and the PCM1808, PCM5102, and audio stages in the upper right. As my transceiver front panel and backplane use 5V logic, I level shifted all interfaces (except one!) from the 3.3v tolerant Teensy to the backplane. With the exception of the 5V regulator on the front side of the board, power regulation is done on the backside of the board.

Teensy 4.1, Transmit and Receive Audio Board schematic.

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