The rules where you live

Three numbers called power

Conducted power is what the radio puts into the cable. Add the antenna's gain in dBi and subtract the cable loss, and you have the radiated power, EIRP. ERP measures the same radiation against a half-wave dipole, so ERP is EIRP minus 2.15 dB.

The rules are about what is radiated. A bigger antenna raises the EIRP with the radio unchanged, so the gain you add has to come off the conducted power. The SX1262 can make 22 dBm. That is a capability, not a permission.

Australia, AU915

On the farm the band is 915 to 928 MHz, under the class licence for low interference potential devices. As the course reads it, the licence allows up to 1 W EIRP, which is 30 dBm, under conditions. For digital modulation one is a power density of 25 mW in any 3 kHz. A signal spread evenly across 125 kHz at 1 W is about 24 mW per 3 kHz, so a narrower signal cannot simply be turned up. The bench shows this as arithmetic with a flat spectrum assumed, not a compliance test.

The LoRaWAN plan for AU915 has 64 uplink channels of 125 kHz, 8 of 500 kHz, and 8 downlink channels of 500 kHz. A network often uses one block of eight, a sub-band. That is the network's choice, not the law.

The class licence sets no duty cycle, needs no licence to buy, and gives no protection from other users. Read the current instrument before building anything.

Other regions

EU868 states its limit in ERP, 25 mW in the 868.0 to 868.6 MHz slice, with a 1% duty cycle or listen before talk, and other slices differ. US915 works under 47 CFR 15.247, whose conditions depend on how the signal is made. The radio, its matching and its antenna are built for a band, so a setting does not make a module right for another one. On the bench they are a comparison, and the farm stays AU915. The next lesson, on shared spectrum, picks up the no-protection point.

Common mistakes

• Treating the chip's maximum as the legal power. The limit applies to what is radiated: conducted power plus antenna gain minus cable loss.
• Mixing up ERP and EIRP. They differ by 2.15 dB, and each rule names its own unit.
• Taking a sub-band for the rule. A sub-band is a network's channel mask, and the law is the licence's conditions.