Introduction
LoRa (Long Range) is a very popular protocol for long range communication between low powered battery operated devices (Ref.1). In the previous three posts I looked at sending a packet using a pair of adjacent 915MHz LoRa transceivers, simulating the LoRa symbols and receiver symbol correlation with Scicos (Ref.2/4). In this post I go on a walkabout to see how far I can travel from a balcony mounted transceiver and still receive a message correctly.
Walkabout Configuration
Parameter | Separation Distance m |
RSSI = -51 | 0 m (adjacent) |
RSSI = -72 | 10 m (inside apartment) |
RSSI = -79 | 50m (Outside Facing) |
RSSI = -88 | 100m (1st Block North) |
RSSI = -104 | 200m (2nd Block North) |
RSSI = -108 | 300m (3rd Block North) |
RSSI = -110 | 400m (4th Block North) |
RSSI = -115 | 500m (5th Block North) |
RSSI = -114 | 600m (6th Block North) Obstructed Church, Houses & Trees |
Figure 1 shows the walkabout configuration. An RPi4B is used as a base unit and is connected to a desktop computer via VNC viewer. A PiTop with RPi3B is used as the portable terminal. A Python program rfm9x_node1/2_ack.py is run on each unit (Ref.5). Each node receives a startup message, then packets 1,2,3….etc until the program is terminated. There is no output on the OLED display but just on the Terminal Program. Figure 4 shows the reception results. At 600m the path was obstructed by a church, several houses and trees. Without these obstructions I am pretty sure I could have gone out to at least 1Km without packet loss.
An RTL-SDR is used to capture the packet transmission with SDR# and is saved as an IQ baseband file for playback and study.
LoRa Signal Capture
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References
#1. – “LoRa Alliance”
https://resources.lora-alliance.org/technical-specifications/rp002-1-0-4-regional-parameters
#2. – “LoRa Scicos Simulation_b”
https://jeremyclark.ca/wp/telecom/lora-scicos-simulation_b/
#3. – “LoRa 915MHz Transceiver Packet Test”
https://jeremyclark.ca/wp/telecom/lora-915mhz-transceiver-packet-test/
#4. – “LoRa Scicos Simulation_a”
https://jeremyclark.ca/wp/telecom/lora-scicos-simulation_a/
#5. – “Python Code for RFM95W”
https://github.com/adafruit/Adafruit_CircuitPython_RFM9x