What is NPR – New Packet Radio?

New Packet Radio – NPR

When an radio amateur thinks of packet radio, they often think of replacing the speaker and microphone inputs to the UHF / VHF radio with a TNC (Terminal Node Controller) then connecting the TNC to a computer and running a special program like WinLink or DireWolf. The TNC is a modem similar to the ones used when we accessed the Internet using “dialup”. The TNC converts the data into signals at audio frequencies to replace the voice signal.

NPR is packet radio but in a way incompatible with the modulation of a TNC. It an open-source protocol for sending data over as a 430 MHz (UHF) signal between two NPR nodes. 430 MHz is generally the amateur radio or “HAM” band so to use NPR you need to be in a country that uses this band for amateur radio and you must have amateur radio license that is valid for the jurisdiction in which you operate an NPR radio.

NPR Specification and Resources

NPR was developed French HAM Guillaume, callsign F4HDK, who has published an open public specification, with a Creative Commons 4.0 license. At time of writing New Packet Radio NPR Specification Version 2.0 Sept 2019 is the latest version and the basis of this article. A good resource for NPR is the project Hackaday Page, which includes open-source design files for the circuit board (PCB) a list of parts (BOM), and assembly information so you can build it yourself from scratch. The page also links to a 3rd party site where you can purchase kits which make it much easier to assemble your own.

What NPR is and How It’s Used

The “New” in NPR refers to using newer (in a relative sense) techniques than traditional packet radio. NPR is designed from the ground up for network support using frames compatible with IPv4 (it does not appear to support IPv6 at thus time) and the interface to the modem is an ethernet cable. When two NPR modems are connected the two networks to which the modems are connected are joined into one large network, subject to IPv4 network routing rules. Compare this to traditional packet radio where the TNC (or modem) is connected via serial (often RS-232) to a computer on each end which then exchange data using AX.25 then dedicated utilities such as WinLink are used to share specific data (such as e-mail for WinLink). With NPR by connecting the ethernet cable, most applications (e-mail clients, web browsers) that use a network connection will just work out of the box with no special software, intermediate computers or setup required. The main limitation is speed, browsing the internet over NPR is no comparison to broadband. There are potential security considerations due to the regulations on encryption in this band. The use of an https:// connection for instance potentially may not comply with the regulations (whereas regular http:// does). This is an area for further investigation.

NPRv05 Modem Hardware

As mentioned above the Hackaday Project Page details how to build a modem from scratch or using a kit. This produces a ‘reference implementation’ of the NPR Specification V2.0. The design is based on the RF4463F30 Module (datasheet) produced by Nice RF in Shenzhen, China. In this article I will use NPR to refer to NPR in general, as it is defined in the specification and NPRv05 to refer to the specific version 5 hardware design detailed on the Hackaday Project Page. There are other vesions, but I will specifically use version 5, hence NPRv05.

The RF4463F30 Module can be purchased directly on the NiceRF website, either by chat on the website or via e-mail. The RF4463F30 is a SoM (System-on-Module), a small PCB, with castellated edges that allow it to be soldered directly onto the main PCB. The SoM contains a number of ICs and including a Silicon Labs Si4463, LNA (Low Noise Amplifier) and discrete components. The use of this module greatly simplifies the design as the analog RF section is largely handled inside the module (hence the need for different modules to cover different bands). The module is pre-configured for a specific unlicensed ISM band: 315MHz, 433MHz, 470MHz, 868MHz, or 915MHz. It turns out that the 433MHz band is an ISM unlicensed band in China but an amateur band in much of the rest of the world (including France, Canada and the US) which is very convenient for this NPR project. The components of the SoM are covered by a metalic shield which helps to reduce interference. However, the shield connections are on the bottom of the SoM and soldering these proved to be a challenge.

NPRv05 NiceRF RF24463F30 / Si4463 Radio Module

Radio functionality in the NPRv05 is provided by the Silicon Labs Si4463 (datasheet) inside the SoM which is connected via a SPI interface to the STM32 microcontroller. Using SPI command, the Si4463 is configured for the operating frequency and modulation. The packet structure is also configured corresponding to the NPR Specification. The Si4463 contains RX and TX FIFO (first in first out) buffers where over-the-air received/transmit packets are stored on their way to and from the microcontroller.

NPRv05 MCU

The NPRv05 uses an ST Micro STM32 L432KC Nucleo board. Nucleo boards usually used for prototyping. However, it is convenient to use because it includes the power circuits, a USB interface for communication, and STLink for programming (flashing) the firmware. The microcontroller is a STM32L432KB. The Hackaday Project Page includes binary firmware images that can be easily be flashed to the MCU. When connected to a computer the board shows up on the host computer. Copying the binary firmware file to the drive results in the MCU being flashed with that image. Images are provided for 70cm (440MHz) and 2m (144MHz). The correct firmware image for the purchased RF4463F30 Module must be used (e.g. 70cm).

NPRv05 Ethernet

Ethernet is provided by a generic USR ES1 W5500 Module (example datasheet) and can be found on AliExpress. It is based on the WizNet W5500 IC (datasheet). The module includes the Ethernet PHY interface and an RJ-45 connector for connecting an ethernet cable. The W5500 interfaces to the MCU over a SPI interface.

NPRv05 Power and Integration

The main NPRv05 PCB provides power, status LEDs, SRAM, and a mechanics substrate and interconnect for the Silicon Labs Si4463, STM32 L432KC Nucleo, and WizNet W5500 Ethernet.

The power supply is constructed in two stages. The first stage is a generic LM2596 (datasheet) based DC to DC Buck Converter module commonly found in places like AliExpress. However many of these modules appear to contain fake LM2596 ICs. These are usable, but care should be taken as they tend to use a lower switching frequency than 150 kHz used by the real Texas Instruments part. This results in less efficiency and more heat being generated. As well there is more ripple in the output. However this should not be a problem as the the output of the module is further regulated by two linear regulators on the NPRv05 main PCB — either a TI LM2937ET-3.3 (datasheet) or an LF33CV (datasheet) voltage regulator for 3.3V and L4940V5 for the 5V supply.

NPRv05 PCB includes a 23LC1024 SPI SRAM (datasheet), which provides the MCU with 128k bytes of non-permanent storage.

The NPRv05 provides status via four LEDs. The PWR LED is driven directly from the 3V3 supply indicating when power (3.3V) is on. The TX LED is driven directly from the Si4463 and the RX and CON LEDs driven by software on the STM32 MCU.

NPR Firmware

Source Code is also provided as a zip file on the Hackaday Project Page. According to the included text file the firmware can be built using either the ARM Mbed CLI, the offline toolchain for ARM Mbed, or GCC_ARM via the makefile. This is a topic for another post.

NPR Schematic

NPRv05 Build Notes

TBD