SDR receiver

Introduction

This is a simple SDR receiver that can be used with GNU Radio.

This application requires the Zmod Digitizer module to be connected to the ZMOD A connector of the USB104 A7 board.

Hardware

The implementation of the SDR receiver is quite straightforward:

• An antenna is connected to one of the inputs of the Zmod Digitizer module
• The on-board ADC (122.88 MS/s sampling frequency, 14-bit resolution) digitizes the RF signal from the antenna
• The data coming from the ADC is processed by a in-phase/quadrature (I/Q) digital down-converter (DDC) running on the FPGA

The tunable frequency range covers from 0 Hz to 122.88 MHz.

The I/Q data rate is configurable and five settings are available: 24, 48, 96, 192, 384, 768 and 1536 kSPS.

The basic blocks of the digital down-converter (DDC) are shown in the following diagram:

The projects/sdr_receiver directory contains two Tcl files: block_design.tcl, rx.tcl. The code in these files instantiates, configures and interconnects all the needed IP cores.

Software

The projects/sdr_receiver/server directory contains the source code of the ZMQ server (sdr-receiver.py) that receives control commands and transmits the I/Q data streams to the SDR programs.

The projects/sdr_receiver/gnuradio directory directory contains flowgraph configuration examples for GNU Radio Companion.

The screenshot below shows GNU Radio Companion running the FM receiver flow graph (fm_zmq.grc) and communicating with the ZMQ server (sdr-receiver.py).

Getting started with GNU Radio on Windows

• Connect an antenna to the CH1 connector of the Zmod Digitizer module
• Connect the USB104 A7 board to a USB port
• Download and unpack the release zip file
• Install the WinUSB driver for the USB interface of the USB104 A7 board (USB ID 0403:6010 and 0403:6014) using Zadig
• Run the sdr-receiver.exe program
• Press the Start button
• Download and install radioconda
• Run GNU Radio Companion and open the FM receiver flow graph (fm_zmq.grc)

Getting started with GNU Radio on Linux

• Connect an antenna to the CH1 connector of the Zmod Digitizer module
• Connect the USB104 A7 board to a USB port
• Install GNU Radio and python3-libusb1:

sudo apt-get install gnuradio python3-usb1

• Install pyhubio:

pip install pyhubio

• Clone the source code repository:

git clone https://github.com/pavel-demin/usb104-a7-notes
cd usb104-a7-notes

• Build the sdr_receiver.bit bitstream file for FPGA configuration:

make NAME=sdr_receiver bit

• Run GNU Radio Companion and open the FM receiver flow graph (fm_usb.grc):

cp tmp/sdr_receiver.bit projects/sdr_receiver/gnuradio
cd projects/sdr_receiver/gnuradio
gnuradio-companion fm_usb.grc

Building from source

The structure of the source code and of the development chain is described at this link.

Setting up the Vitis and Vivado environment:

source /opt/Xilinx/Vitis/2020.2/settings64.sh

Cloning the source code repository:

git clone https://github.com/pavel-demin/usb104-a7-notes
cd usb104-a7-notes

Building sdr_receiver.bit:

make NAME=sdr_receiver bit

Configuring the FPGA:

make NAME=sdr_receiver run