NPR70 — New Packet Radio for 70 cm Band

A complete open-source hardware and firmware project for a modern IP packet radio modem operating on the 70 cm amateur band (420–450 MHz). Compatible with the NPR New Packet Radio, but with custom hardware and improvements for easier DIY assembly.

What is NPR70?

NPR70 is an open-source implementation of a New Packet Radio (NPR) modem — a protocol and hardware design for transmitting IP packets over UHF (70 cm) amateur radio, with the following goals:

• High throughput (typically 50–500 kbps gross rate)
• Reliable point-to-multipoint IP networking (TCP/IP, UDP, etc.)
• Fully open hardware and software
• Minimal latency and straightforward configuration

This project is primarily for amateur radio operators interested in building and experimenting with modern digital data networks, Hamnet, telemetry, or similar applications on the UHF band.

It is a fork/derivative of the original NPR project by F4HDK, but with new custom hardware, simplified design, and refactored/cleaned firmware.

Who is this for?

• Licensed amateur radio operators interested in high-speed IP digital modes
• Hamnet and HSMM enthusiasts
• Anyone interested in open hardware wireless networking on UHF

Hardware Overview

• MCU: STM32 microcontroller (STM32L432KCU, as in original)
• RF Module: NiceRF module for 70 cm UHF band (based on SI4463)
• Ethernet: W5500 (SPI, 10/100 Mbps Ethernet controller)
• Form Factor: Two layer 69×100 mm PCB
• Other: 0402 SMD passives, SMA, Ethernet and USB-C connectors, etc.

The hardware is designed to be compact and affordable, with a focus on DIY manufacturing and community development. All schematics and layout files are in the pcb/ directory.

Firmware Details

• Based on MbedOS 5.6.6 (last version compatible with the original code)
• Derived from the [F4HDK NPR firmware] (https://github.com/f4hdk/NewPacketRadio), but refactored and cleaned up for different pinout
• Supports all main NPR features (TDMA master/slave, 2GFSK/4GFSK, point-to-multipoint IP bridging)
• Compatible with official NPR protocol and other compatible modems

Key Features

Feature	Details
Protocol	NPR (custom IP radio, NOT AX.25; true L3)
Topology	Point-to-multipoint (master + up to 7 clients), TDMA
Modulation	2GFSK / 4GFSK, up to 500 kbps gross (see protocol docs)
RF Band	70 cm amateur band (configurable, typically 430–440 MHz)
Network	Full IP stack, transparent bridging, works with DHCP, TCP/IP, UDP, etc.
Range	Up to 300 km line-of-sight (with suitable antennas and power)
Hardware	STM32 MCU, SI4463 radio, W5500 Ethernet, all open hardware
License	GPL v3.0 (same as original NPR project)

Repository Structure

• pcb/ – KiCAD project directory (schematic and PCB layout).
• src/ – Firmware source code, based on MbedOS (legacy version), derived and adapted from the original NPR project.

Quick Start

1. Hardware: Manufacture or assemble the PCB found in pcb/. BOM and assembly notes are included.
2. Firmware:
   • For building the code by youself, you will need Debian based system and installed gcc-arm-none-eabi.
   • Build firmware by running make in the src/ directory.
   • Firmware binary is in the src/BUILD/NPR70.hex file
   • Flash firmware to the STM32 MCU using an SWD programmer pyocd load -t stm32l432kc BUILD/NPR70.hex
3. Configuration: Adjust radio parameters (frequency, bandwidth, master/client mode, IP addresses) as described in the original NPR documentation
4. Connect: Plug in Ethernet and power, connect antenna, and start experimenting

Basic settings to check (more details in the original NPR documentation):

• display config: show current configuration
• set <param> <value>: store value to the given parameter
• save: saves current configuration into the EEPROM
• radio on/radio off: turn RF on or off
• reboot: reboot the FW

You have to set your callsign, frequency and modulation. Rest of the parameters is up to you and your setup.

set callsign AB1CDE
set frequency 434.200
set modulation 22

Documentation and References

• Original NPR project by F4HDK
• Official NPR documentation (PDFs, guides, protocol)
• Project homepage and build log (in Czech)

License

This project is released under the GPL v3.0 license, same as the original NPR project by F4HDK. See LICENSE for full details.

Contributing

Contributions are welcome! You can:

• Submit hardware design improvements (new PCB revisions, bugfixes)
• Help with firmware optimization, porting to newer MbedOS versions, or adding features
• Share test results, deployment reports, and real-world feedback
• Translate documentation

For major changes, please open an issue first to discuss what you would like to change.

If you have questions or suggestions, feel free to open an issue.