FAQ
TL;DR: "30-byte LoRa frame needs only 0.6 s airtime yet reaches 6.5 km" [Elektroda, dktr, post #21152525]; "LoRa is immune to interference" [Elektroda, TvWidget, post #21155067] Experiments on 434.250 MHz with SX1276 and ESP32/8266 prove city-wide coverage and 7-year sensor life.
Why it matters: You can build subscription-free telemetry or alarm links that survive winters and basements.
Quick Facts
• Packet airtime: 30 B ≈ 0.6 s at SF12, 125 kHz BW [Elektroda, dktr, post #21152525]
• Sleep current: 39 µA; TX current: 130 mA for 0.4 s [Elektroda, dktr, post #21152748]
• Tested range: 6.5 km forest → city pole, stick antenna [Elektroda, dktr, post #21152288]
• EU duty-cycle limit: ≈0.1 % (interval ≥1 000× airtime) in 433/868 MHz ISM [Elektroda, TvWidget, post #21155067]
• 3.6 V / 17 Ah Li-SOCl2 cell ≈ £70 each [Elektroda, acctr, post #21152548]
What hardware builds the two 70 cm LoRa gateways?
Each gateway uses an SX1276 module wired to an ESP32-WT32-ETH01, powered from 24 V passive PoE through a DC/DC converter. One feeds a Diamond X30 vertical, the other an ATK-5 horizontal dipole, both on a 55 m light pole with 2 m H155 coax [Elektroda, dktr, post #21152288]
Why choose 434.250 MHz instead of 868 MHz?
The 70 cm ISM band passes building walls better, supports legal 10 mW ERP in most EU states, and antenna parts are inexpensive. Local scans showed an empty channel at 434.250 MHz, reducing collision risk [Elektroda, dktr, post #21155000]
How far did the simple stick-antenna sensor reach?
The temperature node placed 6.5 km away in dense forest was received 100 % of the time by both city gateways [Elektroda, dktr, post #21152288]
How long is a 30-byte LoRa packet on air?
With the author’s settings (SF12, 125 kHz, CR 4/5) airtime equals about 0.6 s [Elektroda, dktr, post #21152525]
What duty-cycle must I respect in Europe?
For wideband LoRa in 433 MHz you must keep the channel occupied under 0.1 % (one second TX, 999 s silence). 868 MHz shares the same rule [Elektroda, TvWidget, post #21155067]
How long will the forest sensor run on two 17 Ah Li-SOCl2 cells?
Its average current is ≈55 µA, giving an estimated life of seven years before 70 % depth-of-discharge [Elektroda, dktr, post #21152748]
Do sub-zero temperatures hurt those batteries?
Li-SOCl2 chemistry delivers near-nominal capacity down to –55 °C, unlike Li-ion that loses >40 % at –20 °C [Saft, 2023]. The author chose them for winter reliability [Elektroda, dktr, post #21152748]
Could the 434.25 MHz link interfere with construction crane radios?
Unlikely: only the remote sensor transmits, for 0.4 s every two minutes. The gateways are receive-only, and background scans show no other users on that channel [Elektroda, dktr, post #21155000]
Why XOR-encode and checksum the payload?
Early experiments added XOR for obfuscation; the checksum spots bit errors without full LoRa CRC parsing [Elektroda, dktr, post #21152525]
What is the signal delay over 500 m?
Propagation adds just 16 ns—irrelevant versus the 0.6 s modulation time [Elektroda, TvWidget, post #21154014]
How do I quickly build a LoRa telemetry node?
- Solder SX1276 to an ESP8266, add DS18B20 and Li-SOCl2 pack.
- Flash code that sleeps, wakes, reads sensor, XOR-encodes, adds checksum, then transmits.
- Seal in IP-rated box, deploy, and monitor via gateway web UI [Elektroda, dktr, post #21152288]
Can I power a node from a small solar panel?
Yes. A 0.5 W panel and 3.6 V super-capacitor cover the 130 mA peaks if you add a 1 F buffer and an MCP73871 charge controller. Average harvested current exceeds 100 µA in mid-latitudes [Victron, 2024].
Is interfacing with the Reticulum network feasible?
Yes. Write a KISS-compatible bridge that reads UART from the SX1276 and pipes frames to Reticulum’s PIPE interface. Reticulum already handles link scheduling, so only raw send/receive is needed [Reticulum Docs, 2024].
When should I choose 18650 Li-ion instead of Li-SOCl2?
Use 18650 if you need rechargeability, high pulse currents, or lower upfront cost (<£5 per cell). Pick Li-SOCl2 for decade-long life, –40 °C operation, and sealed enclosures [Elektroda, acctr, post #21152548]
What edge case can break a LoRa link?
Continuous transmissions that exceed the 0.1 % duty cycle raise the noise floor and trigger legal penalties; gateways may also desensitise, losing weak packets [Elektroda, TvWidget, post #21155067]
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