LoRa APRS: Bringing APRS into the 21st Century
LoRa APRS represents a significant advancement in the world of amateur radio communication. This innovative technology combines the long-range capabilities of LoRa (Long Range) with the well-established Automatic Packet Reporting System (APRS), offering enhanced performance and exciting new possibilities for radio enthusiasts.
Key Features and Benefits
LoRa APRS operates on a worldwide frequency of 433.775 MHz, providing a unified platform for global communication. This system offers several advantages over conventional APRS:
- Extended Range: LoRa's chirp spread spectrum technology allows for reception of signals far below the noise floor, significantly increasing the communication range compared to traditional APRS.
- Low Power Consumption: LoRa APRS trackers typically transmit at 100mW, making them highly efficient for battery-powered operations.
- Improved Performance: The system can provide location updates, weather information, and text messaging over longer distances than conventional APRS.
- Cost-Effective Hardware: LoRa trackers and iGates can be built using readily available, low-cost consumer off-the-shelf (COTS) hardware.
While LoRa APRS offers these advantages, it's worth noting that traditional APRS benefits from a well-established infrastructure and network effect, having been in use for decades. However, as LoRa APRS continues to grow, it promises to significantly enhance the capabilities of APRS technology, especially in scenarios requiring long-range, low-power communication.
Applications in Amateur Radio
LoRa APRS has found particular favor among Summits on the Air (SOTA) operators. Its ability to function effectively in areas with limited cellular coverage makes it ideal for remote locations and mountainous terrain. The system's low power requirements and long-range capabilities are well-suited for portable operations, allowing SOTA activators to send position reports and receive spots without relying on patchy mobile data connections.
Technical Specifications
LoRa APRS typically uses the following parameters:
- Frequency: 433.775 MHz
- Spreading Factor: 12
- Bandwidth: 125 kHz
- Coding Rate: 4:5
- Output Power: 20 dBm (0.1W)
The IARU International Amateur Radio Union (IARU) Region 1 VHF Handbook 8.50 recommends 433.775 and 433.900 MHz with a bandwidth of 125 kHz. Be sure to check whether the frequency and bandwidth are legal in your country before transmitting.
Rather than using the AX.25 frame format, the LoRa frame payload contains:
· Three byte sequence to distinguish from other LoRa applications: 0x3c 0xff 0x01
· APRS packet in TNC-2 Monitoring format.
Building a LoRa APRS Network
Development so far, has concentrated on two main components:
- Trackers: These devices transmit geographical positions in real-time using LoRa modulation. They are often built using ESP32 LoRa modules, which include a 433 MHz transmitter/receiver, GPS receiver, WiFi module, microcontroller, USB port, OLED display , and often a battery charger.
- IGates: These systems receive frames sent by trackers and inject them into the APRS-IS network via internet access. Forwarding in the opposite direction is usually limited to “messages” addressed to stations recently heard over RF. iGates are typically installed in fixed, elevated positions to ensure wide coverage.
Future Prospects
As LoRa APRS continues to gain traction, it promises to drag APRS into the 21st century. The technology's superior performance, especially in challenging terrains and low-power scenarios, makes it an exciting prospect for the future of amateur radio tracking and communication. While LoRa APRS is primarily focused on position reporting and short messaging, its integration with the existing APRS infrastructure allows it to leverage decades of development in the APRS-IS system and visualization tools like aprs.fi.
Those who think that APRS is watching trackers on aprs.fi do not understand the philosophy behind APRS. In the words of its creator:
“APRS is not a vehicle tracking system. It is a two-way tactical real-time digital communications system between all assets in a network sharing information about everything going on in the local area. On ham radio, this means if something is happening now, or there is information that could be valuable to you, then it should show up on your APRS radio in your mobile.”
“APRS is a real-time tactical digital communications protocol for exchanging information between a large number of stations covering a large (local) area. As a multi-user data network, it is quite different from conventional packet radio.
APRS is different from regular packet in four ways. First by the integration of maps and other data displays to organize and display data, second, by using a one-to-many protocol to update everyone in real time, third, by using generic digipeating so that prior knowledge of the network is not required, AND FORTH, since 1997, a worldwide transparent internet backbone, linking everyone worldwide. APRS turns packet radio into a real-time tactical communications and display system for emergencies and public service applications (and global communications). Normal packet radio is useful in passing bulk message traffic (Email) from point-to-point, but it does not do well at real time events where information has a very short life time and needs to get to everyone quickly.
APRS is a LOCAL RF network. Although the Internet monitors APRS worldwide, this is not the primary objective. But like all of our other radios, how we use APRS in an emergency of special event is what drives the design of the APRS protocol. Although APRS is used 99% of the time over great distances, and benign conditions, the protocol is designed to be optimized for short distance real-time crisis operations on RF.
APRS provides universal connectivity to all stations in the net by avoiding the complexity and limitations of a connected network. It permits any number of stations to exchange data just like voice users would on a voice net. Any station that has information to contribute simply sends it, and all stations receive it and log it. Secondly, APRS recognizes that one of the greatest real-time needs at any special event or emergency is the tracking of key assets. Where is the Event Leader? Where are the emergency vehicles? What’s the Weather at various points in the County? “
– Bob Bruninga, WB4APR (SK)
“APRS is not a vehicle tracking system.” … “APRS is a LOCAL RF network.”
To realize this goal, bridges are needed to connect the two radio networks without requiring Internet connections.
As more radio amateurs adopt this technology and contribute to the growing network of IGates and bridges to traditional APRS, LoRa APRS is poised to become an increasingly valuable tool for the amateur radio community, particularly in applications requiring long-range, low-power communication in challenging environments.
References:
How LoRa Modulation really works - long range communication using chirps
Exploring LoRa APRS: VHF vs UHF Performance
RPi-LoRa-KISS-TNC: a simple software for enjoying LoRa APRS
Optimizing LoRa APRS Tracker for Maximum Battery Life