CaribouLite Raspberry Pi HAT, A Low-Cost Software Defined Radio

December 06, 2021

Blog

Radio communication is becoming extremely important for safety and emergency communication systems during situations like natural disasters and terrorist attacks. Interoperability problems are faced by military and civil safety officials as different aid agencies have radios working in different frequency bands, waveforms, and protocols. Additionally, these radios used need to be low cost, small size, portable and require low power to operate.

Software Defined Radio (SDR) technology helps to solve these problems by implementing radios that can operate on multiple frequency bands and multiple protocols by software control. The combination of the single-board computer, Raspberry Pi (RPi), and the radio transceiver CaribouLite, makes the Software Defined Radio portable, capable, and affordable.

CaribouLite is an open-source, SDR platform that can be implemented as a Raspberry Pi HAT (Hardware attached on top). It is capable of turning a Raspberry Pi single-board computer (SBC) into a self-contained, dual-channel radio with a wide tunable frequency spectrum of up to 6 GHz. It was designed for makers, hackers, educators, and researchers as a high-quality, affordable, standalone SDR building block for the Raspberry Pi SBC. It perfectly complements the current SDR ecosystem. CaribouLite was built for portability. Therefore, all it needs for operation is an RPi and a power source.

What is CaribouLite RPi HAT?

CaribouLite is a fully open-source SDR Raspberry Pi HAT with a tuning range up to 6 GHz, and a dual-channel including TX/RX channels. It supports the standard communication modulations (i.e. PSK, FSK, OFDM, etc.) and also direct I/Q sampling (13-bit x2 - ADC and DAC) directly from the RPI. 

CaribouLite has two versions: the full version and the ISM version. Both the versions include an internal TCXO clock source, whereas the full version comes with a low-noise amplifier (NF < 4dB and under 3GHz) and high Tx power (up to 14dBm). They also have fully controllable 8-bit read/write PMOD expansion ports to enable advanced applications such as GPS synchronization, direction finding, etc..

For the software, Raspberry Pi has advanced APIs like Soapy / GNU Radio and Jupyter notebooks that are supported entirely. Through them, the HAT’s complete feature-set can be accessed.

Frequency Range:

The full version of CaribouLite can transmit and receive in two parallel channels: 

• Channel 1: 30 MHz to 6 GHz
• Channel 2: Sub-1-GHz

Image Credit: CaribouLite

The immediate bandwidth (2.5MHz with 4 MSPS ADC and DAC) is sufficient for most IoT communication. The 4 MSPS I/Q samples (both Tx and Rx) are transmitted over the RPi’s secondary memory interface, where CaribouLite is like a high-throughput memory peripheral. The ISM version of CaribouLite supports the native 2.4-GHz and sub-1-GHz bands available within the Microchip chipset used.

CaribouLite RPi HAT Specifications

Let’s take a look at the CaribouLite RPi HAT Specifications:

1. Modem: AT86RF215
2. FPGA: ICE40LP1K
3. Synth. Integrated Mixer: RFFC5072(A) 
4. Tuning Range: CH1: 30 MHz - 6 GHz, CH2: Sub-1GHz
5. Transmit Power: up to 14 dBm (i.e. ISM frequencies)
6. Bus/Interface: SMI (Raspberry Pi)
7. Multi-Board Synchronization: Clock and Data
8. Connectors: 6 GHz SMA connector, Sub-1-GHz SMA connector, PMOD connector (8-bit I/O, GND and 3.3V), RPI 40-pin connector
9. Operating System: Linux (Raspberry Pi dependent)
10. Dimensions: 1,950 mm² (65 x 30 mm)

Image Credit: CaribouLite

Image Credit: CaribouLite

What can you do with CaribouLite RPi HAT?

The following is what the SDR can do that weren’t possible before:

• Software-defined radios can be reconfigured while in progress i.e., the universal communication device would reconfigure itself appropriately for the environment. It could be a cordless phone, a cell phone, a wireless Internet gadget, and a GPS receiver
• Software-defined radios can be swiftly and easily upgraded with enhanced features. In fact, the upgrade could be delivered while it is in motion
• Software-defined radios can talk to and hear multiple channels at the same time
• New kinds of radios can be built that have not been in existence. Smart radios or cognitive radios (CRs) can use the RF spectrum in their immediate neighborhood and configure themselves for the best performance

Being a fully open-source SDR, CaribouLite allows one to customize it to suit their own needs. It helps by providing complete source codes and thorough documentation, including toolchain and programming guidelines. They provide custom, step-by-step application guides (FPGA, C, C++, Python, etc.), and a library to support applications like:

• Analog-FM/Digital-DAB+ radio receivers and basic signal recording
• ADS-B receivers
• Signal relays
• Signal/protocol generators

Final thoughts on CaribouLite RPi HAT

The CaribouLite RPi HAT system has a number of attractive features such as being low cost, small size, low power consumption, easy to carry, easy to configure, and easy to deploy. One major advantage of this system is that it has a significantly low cost as compared to other SDR solutions available in the market. 

One of the facts that makes it special is the use of Raspberry Pi, which provides sufficient processing power for performing digital signal processing tasks. The use of Raspberry Pi makes integration of the front-end very easy into one single compact device using various peripherals like USB, Ethernet, etc. The system can be operated using a portable battery which makes it easier to carry around.

This is a huge improvement for the user community as it is so economical. The same hardware could be used for a number of applications ranging from a spectrum analyzer, to a BlueTooth beacon, to a ZigBee repeater, to a universal RF remote just by changing the software.

You can visit the crowdfunding page of the CaribouLite RPi HAT for more information.