Thank you to David for submitting news about his company Caribou Labs new product called "CaribouLite" which will be a software defined radio HAT for the Raspberry Pi 4. The product is currently in the pre-launch stage over on Crowd Funding platform CrowdSupply and you can sign up for future updates on the release. David writes:

I'd like to inform you of a product we have developed called CaribouLite board, which is essentially a Raspberry Pi HAT that enabled up to 6GHz SDR capabilities Tx and Rx, and an additional TxRx Sub 1GHz channel.

It uses Microchip's modem AT86RF215 as an I/Q ADC, DAC and frequency conversion is done using Qorvo's RFFC5072 IC. An FPGA (ICE40) is used to stream data packets (I/Q @ 13 bit x2 / sample) back and forth between the Raspberry Pi and the Modem, over an interesting fast interface called SMI.

I think this project brings new ideas to the table and would be interesting to the SDR community.

The use of the SMI interface is an interesting idea and not something we see utilized often as apparently the official documentation is sparse and poor. But David notes how it allows for up to 500Mbit/s of data to be exchanged between the FPGA and Raspberry Pi, but the true throughput depends on the specific Raspberry Pi model used. Regardless the SMI data rate is more than enough for the 120 MBit/s required by the two streams of 13-bit IQ data that the CaribouLite generates.

The campaign also notes that the sample rate is 4 MSPS, with 4 MHz bandwidth, and up to 14 dBm of transmit power is possible. They also note that they are planning to release a wide range of library code that allows for use cases such as wide range spectrum analysis, a signal / protocol generator, an analog / digital DAB+ receiver, an ADS-B receiver and more.

The software and hardware design is also fully open source and available on GitHub.