Most of us get annoyed when we lose a cell signal on our smartphones when we’re slightly out of range to the nearest tower, and unless you’re in a remote area, that signal is typically restored when we get back within range. Depending on the technology, landscape features, and transmitter power, cell towers can have a range between 22 and 45 miles. By contrast, radio signals can have a range of hundreds to thousands of miles, depending on the type of radio and its operating frequency.
As with all technology, engineers and makers had found a way to use a ham radio as a platform for long-range data networking, which is what Guillaume (F4HDK) did when he designed his New Packet Radio (NPR).
“NPR (New Packet Radio) is a custom radio protocol, designed to transport bidirectional IP traffic 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).”
F4HDK built the NPR around a Silicon Labs Si4463 EZRadioPRO ISM transceiver, which is connected to a Mbed Nucleo STM32 L432K microcontroller outfitted with an Arm Cortex-M4 CPU. Since the ISM transceiver is meant for short-range applications, F4HDK boosted the signal using a 20-watt amplifier from hand-held radios developed for the EU DMR (Digital Mobile Radio) standard. The microcontroller was paired with an Ethernet module, which can then be connected to a PC or laptop running the NPR protocol.
The setup produces a few hundred milliwatts of RF, which is then piped through the amplifier and sent out via an omnidirectional antenna. Anyone interested in recreating F4HDK's NPR can find a detailed walkthrough on his project page, complete with documentation and a bill of materials.