Last month we did range testing on a new LoRaWAN radio network installation in Gamboa, Panama. The network, which covers the entire center of town is part of the Digital Naturalism Lab’s commitment to supporting wildlife and environmental research. Gamboa, where the Smithsonian Tropical Research Institute’s laboratory is located, is surrounded by the Soberanía National Park, a large, intact tropical forest that’s jam-packed with rainforest wildlife and flora. Doctoral students and researchers laboriously visit multiple sites daily to collect data that could easily be transmitted in real time wirelessly at low cost over a public science data network. That’s our goal.
LoRaWAN is a long-range, low-bandwidth protocol that operates in the 915 MHz frequency range. We are using a MultiTech Conduit gateway that is configured to pass data through The Things Network, a community-supported global network for LoRaWAN data. To test this base station’s range I created a GPS-enabled signal strength measurement tool using a Pycom LoPy4 wireless microcontroller and Pytrack GNSS development board. The code, written in MicroPython, takes a GPS reading and transmits it to the base station, where the signal strength is measured and passed along with the location through TTN’s server. The resulting data was easily transformed into a map that shows the signal strength recorded at each location.
We compared two different setups:
- A smaller indoor antenna that came with the MultiTech Conduit gateway, located inside the house near a window on an upper floor. This was tested by walking at street level around Gamboa with the Pycom setup.
- A 2-meter-long roof antenna, held in the hot sun on the roof of the house. This antenna sourced from Alibaba is an outdoor antenna nominally for 900 MHz frequencies. We used a short 30 cm cable to connect it to the Conduit router, also located on the roof. The setup was also tested from street level, this time from the back of a pickup truck driving slowly around Gamboa.
We got a surprise! The indoor setup with the small antenna worked significantly better than the large roof antenna. This is most likely due to degraded performance of the roof antenna itself, rather than its prime location or the short cabling. We are pretty convinced that the Alibaba antenna simply wasn’t up to snuff. For the moment, I’m recommending that we continue with the stock antenna in the current location until we can get an outdoor setup that can be proven superior.
Here’s our testing results. The number next to each is the received signal strength indicator (RSSI) in dBm. If you click on a test location you can also see the signal-to-noise ratio (SNR) listed below the RSSI number.
Interactive map: Indoor antenna test:
Interactive map: Outdoor antenna test:
These tests were a lot of fun to do and the results saved Dinalab from installing an antenna that would have reduced system performance, so they were a big success. The Pycom equipment was easy to set up and configure as usual. My MicroPython code and our raw data file results can be downloaded here.