I’d like to transmit data from a buoy floating in the water to a base station on shore. Power consumption and broadcast range are primary considerations. The amount of data being transmitted is expected to be minimal.
I purchased two of the Adafruit RFM95W LoRa Radios to see if this might be a suitable solution. They were fairly inexpensive so I figured it was worth a test. The modules transmit on a license-free frequency and the Adafruit website says signals can travel 2 km – 20 km (1.4 – 12.4 miles) depending on the type of antenna used.
During the Thanksgiving holiday I had the opportunity to test the range of two LoRa radios in a neighborhood in Eugene, Oregon. I wired up an Arduino Uno and Pro Trinket following the Adafruit provides tutorial, see their tutorial for all the details.
The Pro Trinket was setup as the Transmitter, this was located at the house. The Uno was setup as the Receiver and plugged into my laptop so I could watch the serial monitor as I walked around the neighbor hood. I was happily surprised, the radios transmitted one mile through in the suburban area with lots of trees and buildings in the way. While this isn’t ground breaking news, it was nice to conduct a real-world test and verify the websites claim. Below is the google maps screen shot from my phone that was used to verify the distance of approximately one mile.
Unfortunately I had to end the walk-about when it began to rain. But I plan to conduct more range tests to see how far these little radios and -2dB quad band antennas can broadcast. One interesting observation: I was not getting all of the data being sent from the transmitter at the house. The simple “hello world” example sketch included a counter to track the number of messages being sent out by the transmitter. At the end, it appears that every fifth message was being received. I’ll need to learn more about mitigating this issue in the future, but for now this is a good enough “first test”.
Terrain will play in big factor in determining maximum range, so I’d also like to run another test over a large body of water to see how the signal attenuates. This would be more similar to the conditions experience when the buoy is deployed. Maybe I can use a kayak and deploy a really simple buoy in the harbor and see if I can receive a message from my office building in Sausalito, CA.
More exploration onto the world or radios is needed!