Spreading factors: According to SX1276 datasheet: At SF 6, SNR of -5dB is required At SF 12, -20dB. 2.5dB change between SFs.

During a test with Heltec Wireless Tracker, I received on the edge of the usable range: RSSI: -123dBm, SNR:-17.3dB

SNR(dB) = sig(dB) - noise(dB) -noise = SNR - sig noise = sig - SNR noise = -123dBm + 17.3dB = -105.7dBm

Meshtastic was on the default LongFast setting, which uses:

TX power 27dBm (500mW). SF 11 Link budget (from meshtastic docs): 148.5dB “The link budget used by these calculations assumes a transmit power of 17dBm and an antenna with 0dB gain”

SF 11 requires -17.5dB SNR, so SNR was just acceptable by spec.

In a later test, with VeryLongSlow, lowest RSSI seen with connection was -124dB and -6.0dB SNR, so not better.

• e.r.p is power equivalent to that input to a perfect dipole.
• e.i.r.p is power to an isotropic radiator.
• Perfect dipole has 2.15 dBi gain.

500mW e.r.p (27dBm) is allowed from 869.40 to 869.65 MHz, with max 10% duty cycle, or another interference reduction method. Regulations: IR2030/1/19, EN 300 220. This is just a small portion near the top of the 868 MHz band. Most of it has lower power limits.

IR2030, Ofcom

Further limits on usage in relation to LoRa one may see are probably just rules of The Things Network.

The Things Network uses channels defined by LoRaWAN people, with max 16dBm (40mW) eirp. Most of the frequencies I see in the linked ofcom document though are max 25mW or 10mW erp. (40mW eirp is around 25mW erp though, maybe that is it.)

Power limits are lower than 868MHz but propagation losses should be less. Worth considering. 433 MHz LoRa modules can also be used under amateur radio terms. I suspect noise and channel utilisation maybe the more important factors in band choice. Also consider antenna size, and similarity to

30dBm (1W) limit. Also an amateur band.

Canadian Band Plan

868 MHz band is not available for UK amateurs, but 433 MHz is. 433MHz amateur band also contains licence exempt space that can be used by LoRa.

UK Amateur Bandplan