LoRaWAN Spreading Factor Workbench

Tune SF7-SF12 and watch symbol time, data rate, airtime, link margin, duty-cycle pressure, and ADR trade-offs change together.

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Interactive LoRaWAN spreading factor workbench with airtime formula tracing, chirp symbol timing, link-budget margin, capacity pressure, ADR guidance, and corrected orthogonality caveats.
SF7-SF12 Airtime formula Link margin ADR trade-off

LoRaWAN Spreading Factor Workbench

Tune spreading factor, bandwidth, coding rate, payload size, and distance. The same setting updates the chirp symbol, airtime, link margin, duty-cycle pressure, and capacity warning so the trade-off stays visible.

SF10 Selected spreading factor
8.19 ms Symbol time at selected bandwidth
371 ms Payload time on air
+14 dB Teaching link margin

Scenario

Choose a deployment pattern, then adjust the physical and LoRa parameters. The model is intentionally transparent rather than pretending to be a site survey.

Spreading factor

8 B51 B
0.2 km15 km
Beginner ramp

At a fixed bandwidth, each higher SF doubles chips per symbol and symbol time. That makes weak signals easier to detect, but every message occupies the channel longer.

Quality guardrail
  • Range is model-based, not guaranteed.
  • SFs are quasi-orthogonal, not magic collision immunity.
  • ADR is best for mostly stationary devices.
Margin target met SF10 is slower than SF7, but this teaching model keeps around 10 dB of link margin.
977 bps Nominal physical bit rate at CR 4/5
-132 dBm Example receiver sensitivity
LoRa spreading factor visual model A gateway coverage model, selected device distance, chirp symbol timing, and airtime bars update from the chosen spreading factor. Link-budget teaching map Chirp symbol timing Range is a teaching estimate, not a site-survey guarantee. Gateway RX sensitivity Device 5.0 km Estimated 10 dB range: 7.0 km time within one symbol frequency 1024 chips per symbol Tsym 8.19 ms Data rate Airtime
Airtime pressure
Airtime is moderate. Higher SF or larger payloads quickly raise channel occupancy.
Link margin
Margin is above the 10 dB teaching target.
Capacity effect
Longer airtime raises collision and duty-cycle pressure for the same message rate.
Teaching note: SF selection is a margin and capacity choice, not a fixed distance table.
Diagnosis

The selected SF keeps useful margin, but the airtime cost is visible. Try lowering SF until the link margin falls near the target.

ADR guidance

For stationary nodes with stable uplinks, ADR should usually push toward the lowest SF that keeps enough margin.

Misconception check

Higher SF improves sensitivity by a few dB per step; it does not simply double real-world range.

SF Chips/symbol Symbol time Bit rate Airtime Example sensitivity Comment
Independent learning reference
Formula trace
  • Symbol time: Tsym = 2^SF / bandwidth.
  • Nominal bit rate: SF * bandwidth / 2^SF * coding-rate.
  • Airtime includes preamble, header, CRC, payload symbols, coding rate, and low-data-rate optimization.
Technical caveats
  • Example sensitivity values vary by radio, noise figure, bandwidth, implementation, and data rate.
  • SFs are quasi-orthogonal. Near-far effects, gateway demodulator limits, and interference still matter.
  • Regional data-rate plans map SF and bandwidth differently, so verify the target region profile.
LoRaWAN Regional Parameters RP002 Official regional data-rate and channel-parameter reference. Semtech LoRa and LoRaWAN guide LoRa modulation background, spreading factor trade-offs, and deployment context. The Things Network SF guide Practical spreading factor, airtime, and data-rate explanations for LoRaWAN learners.