NPR (New Packet Radio) is a custom radio protocol, designed to transport bidirectional IP trafic over 430MHz radio links (ham radio frequencies 420-450MHz). This protocol is optimized for "point to multipoint" topology, with the help of managed-TDMA.
Bitrate is up to 500kbps (net, effective bitrate).
The radio modem is cheap (~80$) and home-made, with a 433MHz ISM module inside. The modem is connected locally with Ethernet, therefore no specific software is needed on PC.
The modem is easy to build and reproduce.
You can add a DMR radio amplifier in order to achieve 20W radio power or more.
The main usage is an extension of HSMM - Hamnet - AREDN networks.
All the project is open-source : hardware, software, protocol specification.
The modem can now drive an external PA with its GPIO port
In case of SPI SRAM present (auto detected), the TX data buffer is increased to 128kB instead of 16kB previously. Big improvement of the quality of IP connection.
Radio connection establishment time greatly reduced.
TX_test feature finally debugged and stable.
Documentation updated ("Advanced user guide" and "Assembly and programming guide") mainly about SPI-SRAM, about PTT ouptut, and about firmware upgrade.
Important info about SPI-SRAM : The RAM of the microcontroller used is too limited to have good performances, especially at Master side.
The usage of additionnal SPI-SRAM chip improves greatly performances, especially for Masters, by increasing the TX buffer length, and the SRAM chip is automatically detected and activated with the recent firmware 2020_02_23.
Modems v02 and v03 already have this SPI-SRAM chip.
Modems v04 (the one sold by Elekitsorparts-Funtronics up to march 2020) don't have the SPI-SRAM (it's my mistake, sorry).
You can upgrade the hardware of a modem v04 via adding a SPI-SRAM add-on board.
In order to determine if you need SPI-SRAM upgrade, read the dedicated paragraph inside the "advanced user guide".
You can buy these SPI-SRAM add-on boards from : - Western-Europe : contact me f4hdk[at]free[dot]fr . Warning, I have limited production capacities. - rest of the world : soon available at Funtronics - Elekitsorparts
20th Jan 2020:
Advanced user guide updated, mainly in order to clarify IP config of modems (client modems). Refer to revision history.
Important info: The solution 1 for upgrading the RAM (see below) is feasible, with external SPI SRAM. I will provide soon (february) cheap add-on SRAM boards, and a new firmware (compatible with and without this SPI-SRAM). For modems v04 only. v02 and v03 already have the SPI-SRAM, and the future version v05 will have it also.
1st Jan 2020:
Documentation updated (advanced user guide and introduction) : command "TX_test", adding a fan on the amplifier, setting the MTU to 750 for better performances.
Important info : for future features, especially for the Masters, and for improving performances (buffer size), the RAM of the microcontroller is not big enough (64kB). I have 3 options, not decided yet, currently the 3 are under test:
Solution 1 (prefered): use the existing SPI-SRAM (23LC1024) of PCB v02 or v03. For PCB v04, I could provide a (very) cheap add-on board, easy to solder on top of the Nucleo. It's a shame that I removed this chip inside v04, I'm very sorry, I thought is was useless...
Solution 2: use an external SPI-SRAM in QSPI configuration. The existing PCBs (v02, v03, v04) are not compatible at all, new PCB needed.
Solution 3: use a brand new microcontroller (Nucleo L476RG), with a totally new PCB, larger.
8th Dec 2019:
Document "advanced user guide" updated, refer to "revision history" inside.
I have implemented the FDD (Frequency Division Duplex) feature, which is optional. You can now use separated frequencies for downlink and uplink (frequency shift), with one single modem at client side, and 2 modems and a RF duplexer at Master side (one modem for RX, one for TX).
New firmware released, and documentation (introduction, and advanced user guide) updated accordingly.
29th Sept 2019:
I have tested the PA (power amplifier) P8X from DF2FQ. Not recommended for use with NPR, because it does not integrate an RX-preamplifier, which is needed in order to compensate poor RF4463 sensitivity. Refer to "Advanced user guide" annex 4.
15th Sept 2019:
Sale is temporarily stopped. A new sale will start end of october, shipping world-wide.
New modulations parameters. I switch to GFSK instead of GMSK, with...
Please feel free to comment these lists of evolution, and express your requests, or your priorities. Either here or in the public chat.
Better FEC algorithm, because currently it is very poor. If you can give me some help, I don't understand a lot standard FEC algo (with all these Maths).
Regular temperature check and re-calibration of SI4463 if necessary -> done! (firmware 2019_06_16 and above)
Increase to 15 clients instead of currently 7 maxi. → Probably not feasible with current hardware at Master side, not enough RAM (new hardware under study)
Possible evolutions, if people are interested (raw order, no priority order):
Static IP management of some modems → Removed because you can use future "L2 pure ethernet transport feature" which will be more flexible
Management via pure serial port (instead of USB)
L2 Ethernet transport configuration (instead of currently L3 IPv4); could enable more flexibles topologies, and IPv6 compatibility. But a little bit less efficient.
Extension of frequency range to 420-450MHz instead of currently 430-440MHz (IARU region 1 limits) -> done! (firmware 2019_06_16 and above)
Other modulation parameters, with lower datarates, in order to decrease RF bandwidth -> Done (firmware 2019_06_16 and above)
QoS necessary in order to transport VoIP data over an NPR network
Totally new design, microcontroller with more RAM, PCB optimized for automatic PCB assembly line. Goal would be to mass produce fully assembled modems. Probability low, only if enough people are interested.-> Cancelled feb 2020. The current hardware is already "mass produced" by Funtronics - Elekitsorparts
Frequencies split between uplink and downlink (in case you use NPR Master in a tower where a UHF FM repeater is already present). Additionally, the Master could be used in "FDD" (Frequency Division Duplex) mode in order to use these 2 frequencies simultaneously, like 2G or 3G mobile phones. 2 modems required at Master side. Complex! --> done! (20th oct 2019)