What are the RF requirements for a LoRa device and how does the spreading factor affect range?
LoRa RF and Spreading Factor
LoRa achieves its remarkable range by trading data rate for sensitivity, using chirp spread spectrum to demodulate signals well below the noise floor.
Frequently Asked Questions
How do I choose the right spreading factor?
LoRaWAN ADR (Adaptive Data Rate) automatically selects the SF: devices close to the gateway use SF7 (fast, minimum airtime). Devices far from the gateway use SF12 (slow, maximum range). If you are designing a private LoRa network (not LoRaWAN): start with SF10 as a good balance. Test the actual link quality and adjust SF up (for range) or down (for throughput). Rule of thumb: use the lowest SF that gives reliable communication (< 5% packet loss).
Can different spreading factors coexist?
Yes. LoRa SFs are orthogonal: a receiver tuned to SF7 will not demodulate an SF12 signal, and vice versa. This means: a single gateway can receive multiple devices transmitting simultaneously on different SFs on the same channel. This is equivalent to a form of code-division multiple access (CDMA). A typical LoRaWAN gateway listens on 8 channels, each supporting SF7-SF12 simultaneously = up to 48 virtual channels.
What limits LoRa range in practice?
In rural LOS: 10-15 km is routine (confirmed by many real-world deployments). In urban environments: 1-5 km due to building shadowing, multipath, and interference. In dense urban (city center): 500 m-2 km. In basements/underground: 100-500 m (severe penetration loss). The limiting factor is rarely the link budget (which is extreme at 161 dB) but rather the obstruction and multipath losses that can exceed 50 dB in dense environments.