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CaribouLite

CaribouLite is an affordable, open-source SDR platform that is also a certified HAT for the Raspberry-Pi family of boards (40-pin versions only). It is built 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.

Top View
Top view

Unlike many other HAT projects, CaribouLite utilizes the SMI (Secondary Memory Interface) present on all the 40-pin RPI versions. This interface is scarcely documented by both Raspberry-Pi documentation and Broadcomm's reference manuals. An amazing work done by https://iosoft.blog/2020/07/16/raspberry-pi-smi/ (code in https://github.com/jbentham/rpi) in hacking this interface contributes to CaribouLite's technical feasibility. The SMI interface should allows exchanging ~500+ Mbit/s between the RPI and the HAT, and yet, the results vary between the different versions of RPI. The results further depends 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. Such channel requires 4 bytes (samples padded to 32-bit) per sample (and I/Q pair) => 16 MBytes/sec which are 128 MBits/sec. By packing the samples into 24 bit I/Q pair (converting to 12-bit samples by decimating the samples), this required throughput decreases to 96 Mbit/sec. The AT86RF215 IC from 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.

Deeper project details can be found in our Wiki pages - https://github.com/babelbees/CaribouLite/wiki

Specifications

RF Channels:

  • Sub-1GHz: 389.5-510 MHz / 779-1020 MHz
  • Wide tuning channel: 30 MHz - 6 GHz (excluding 2398.5-2400 MHz and 2483.5-2485 MHz)
spectra
Applicable spectra, S1G - sub-1GHz, WB - Wide tuning channel
Note: The gaps are defined by the design constarints of the system and may not exist in real-life hardware.

FPGA specifications:

  • 160 LABs / CLBs
  • 1280 Logic Elements / Cells
  • 65536 Total RAM bits
  • 67 I/Os, Temp: -40-100 degC

Applicable RPI models: RPI_1(B+/A+), RPI_2B, RPI_Zero(Zero/W/WH), RPI_3(B/A+/B+), RPI_4B

Prices @ 2500 units:

  • Total: <$38.5
    • BOM: ~$35
    • PCB: <$1
    • PCBA: <$2.5
Parameter Sub-1GHz Wide Tuning Channel
Frequency tuner range 389.5-510 MHz / 779-1020 MHz 30 MHz - 6 GHz (excluding 2398.5-2400 MHz and 2483.5-2485 MHz)
Sample rate (ADC / DAC) 4 MSPS 4 MSPS
Analog bandwidth (Rx / Tx) <4 MHz <4 MHz
Max Transmit power 14.5 dBm >14 dBm @ 30-2400 MHz, >13 dBm @ 2400-6000 MHz
Receive noise figure <4.5 dB <4.5 dB @ 30-3500 MHz, <8 dB @ 3500-6000 MHz

Board Layout

2d_nums

Description:

  1. Rasperry-Pi 40-pin connector
  2. A modem - AT86RF215
  3. TCXO - 0.5 ppm @ 26 MHz
  4. FPGA - ICE40LP serier from Lattice Semi.
  5. A frequency mixer with integrated synthysizer - RFFC5072
  6. External reference clock connector (may be used to acheive coherence between many CaribouLite units.
  7. A PMOD connector for FPGA expantion
  8. RPI configuration EEPROM (following RPI-HAT specifications)
  9. RF front-end - switched, amplifiers, and filters.
  10. Reset switch
  11. User custom switch + RPI HAT EEPROM reconfiguration (write-enable) switch
  12. Wide band SMA connector
  13. Sub 1-GHz SMA connector