CaribouLite a new open source Raspberry Pi SDR HAT will soon be available to purchase from the Crowd Supply website offering an affordable, educational, open-source SDR platform offering up to 6 GHz tunable range. Specifically designed for the Raspberry Pi 40-pin mini PC range the open source board has been designed for makers, hackers, and researchers and was designed to complement the SDR current eco-systems offering with a scalable, standalone dual-channel software-defined radio. As a fully open source SDR, users can reprogram, modify and improve CaribouLite’s capabilities for their own custom use.
“Unlike many other HAT projects, CaribouLite utilizes the SMI (Secondary Memory Interface) present on all the 40-pin RPI versions. This interface is not thoroughly documented by both Raspberry-Pi documentation and Broadcomm’s reference manuals. An amazing work done by Lean2 (code in git repo) in hacking this interface contributes to CaribouLite’s technical feasibility. A deeper overview of the interface is provided by G.J. Van Loo, 2017 Secondary_Memory_Interface.pdf. The SMI interface allows exchanging up to ~500Mbit/s between the RPI and the HAT, and yet, the results vary between the different versions of RPI. The results further depend on the specific RPI version’s DMA speeds.”
“In our application, each ADC sample contains 13 bit (I) and 13 bit (Q), that are streamed with a maximal sample rate of 4 MSPS from the AT86RF215 IC. This channel requires 4 bytes (samples padded to 32-bit) per sample (and I/Q pair) => 16 MBytes/sec which are 128 MBits/sec. In addition to the 13 bit for each of I/Q, the Tx/Rx streams of data contain flow control and configuration bits. The modem (AT86RF215) IC by Microchip contains two RX I/Q outputs from its ADCs (one for each physical channel – sub-1GHz and 2.4GHz), and a single TX I/Q intput directed to the DACs.”
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