• LoRa
  • Intermediate
  • 8 min
  • Transmit

Recipe · Intermediate · LoRa

How to send a LoRa packet with SX1262

Estimate airtime, transmit one small text or hexadecimal payload and confirm it on your own authorized receiver.

SX1262 LoRa module and chirp waveform.
A useful transmit test starts with one short packet, a known peer and an explicit modem profile.

Keep the first transmission controlled

Use two nodes you own or are authorized to test, keep them nearby and fit the correct antennas. Confirm the permitted frequency, power, bandwidth and duty cycle for your region before transmitting.

  • Start with one short packet, not a repeated stream.
  • Keep the receiver open on the exact same LoRa profile.
  • Record payload, airtime, RSSI and SNR in the same test note.
Step 1

Verify both endpoints

Run status on the transmitter and receiver. Frequency, bandwidth, SF, CR, sync word, CRC and IQ mode must be compatible.

Step 2

Estimate airtime before TX

The implementation calculates time-on-air from the active modem profile and payload length. A short payload can still have substantial airtime at a high spreading factor.

Step 3

Send one text packet

Open receive on the peer first. The sender previews length, airtime, HEX and ASCII before it transmits.

Confirm the complete path

The peer should report the same payload plus packet RSSI and SNR. A sender-side sent result alone does not prove that the receiver decoded it.

Step 4

Send an exact binary payload

Use two-digit hexadecimal bytes when text would change or hide the payload. The maximum payload is 255 bytes.

Optional repeated bench test

spam repeatedly sends the same payload and treats the last numeric token as the interval in milliseconds. The accepted interval is 1–600000 ms; press Enter to stop and print the summary.

Do not choose an interval from syntax alone

The firmware range is not a legal duty-cycle calculation. Base the interval on measured airtime and applicable regional rules, and stop as soon as the controlled receiver test is complete.

Troubleshooting

  • Invalid payload: use plain text or complete two-digit bytes inside hex{ }.
  • Payload too long: reduce it to 255 bytes or fewer.
  • TX reports failed: check BUSY, power, antenna and the configured oscillator, then inspect status.
  • TX succeeds but RX is empty: compare the full modem profile and confirm the receiver was active before transmission.
  • Repeated test causes losses: lengthen the interval and compare it with airtime, receive processing and applicable duty-cycle limits.

Next steps

  • Repeat single-packet tests at controlled distances and compare RSSI, SNR and error counters.
  • Use scan and waterfall as energy observations, not as proof that a LoRa packet decoded.
  • Capture one known packet to a versioned .lora file for a repeatable lab fixture.

LoRa transmit FAQ

Which payload formats does send accept?

Plain text or hexadecimal bytes inside hex{ }. Invalid or empty payloads are rejected, and the limit is 255 bytes.

Does send show airtime before transmitting?

Yes. It prints length, calculated airtime and a HEX/ASCII preview before starting the radio transmission.

When should I use spam?

Only for a short authorized repeated-packet bench test with an interval derived from airtime and regional limits. Press Enter to stop.

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