5.2 KiB
Radio settings
We use the same channel maps as LoRaWAN (though this is not LoRaWAN).
See this site for more information.
LoRaWAN Europe Frequency Band
The maximum power allowed is +14dBm ERP (Effective Radiated Power, see this site for more information).
433 MHz
There are eight channels defined with a 0.2 MHz gap between them. Channel zero starts at 433.175 MHz
870 MHz
There are eight channels defined with a 0.3 MHz gap between them. Channel zero starts at 865.20 MHz
LoRaWAN for North America
LoRaWAN defines 64, 125 kHz channels from 902.3 to 914.9 MHz increments.
The maximum output power for North America is +30 dBm ERP.
The band is from 902 to 928 MHz. It mentions channel number and its respective channel frequency. All the 13 channels are separated by 2.16 MHz with respect to the adjacent channels.
Channel zero starts at 903.08 MHz center frequency.
Data-rates
About
Various data-rates are selectable when configuring a channel and are inversely proportional to the theoretical range of the devices.
Considerations:
- Spreading Factor - How much we "spread" our data over time.
-
- Each step up in Spreading Factor dobules the airtime to transmit.
-
- Each step up in Spreading Factor adds about 2.5db extra link budget.
- Bandwidth - How big of a slice of the spectrum we use.
-
- Each doubling of the bandwidth is almost 3db less link budget.
-
- Bandwidths less than 31 may be unstable unless you have a high quality Crystal Ossilator.
- Coding Rate - How much redundency we encode to resist noise.
-
- Increasing coding rate increases reliability while decrasing data-rate.
-
- 4/5 - 1.25x overhead
-
- 4/6 - 1.5x overhead
-
- 4/7 - 1.75x overhead
-
- 4/8 - 2x overhead
Pre-Defined
We have four predefined channels. These are the most common settings and have been proven to work well:
| Channel setting | Alt Channel Name | Data-rate | SF / Symbols | Coding Rate | Bandwidth | Link Budget |
|---|---|---|---|---|---|---|
| Short range (but fast) | Short Fast | 21.875 kbps | 7 / 128 | 4/5 | 125 | 134dB |
| Medium range (but fast) | Medium | 5.469 kbps | 7 / 128 | 4/5 | 500 | 140dB |
| Long range (but slower) | Long Alt | 0.275 kbps | 9 / 512 | 4/8 | 31 | 153dB |
| Very long range (but slow) | Long Slow | 0.183 kbps (default) | 12 / 4096 | 4/8 | 125 | 154dB |
The link budget used by these calculations assumes a transmit power of 17dBm and an antenna with 0dB gain. Adjust your link budget assumptions based on your actual devices.
Custom Settings
You may want to select other channels for your usage. The other settings can be set by using the Python API.
meshtastic --setchan spread_factor 10 --setchan coding_rate 8 --setchan bandwidth 125
After applying the settings, you will need to restart the device. After your device is restarted, it will generate a new crypto key and you will need to share the newly generated QR Code or URL to all your other devices.
Some example settings:
| Data-rate | SF / Symbols | Coding Rate | Bandwidth | Link Budget | Note |
|---|---|---|---|---|---|
| 37.50 kbps | 6 / 64 | 4/5 | 500 | 129dB | Fastest possible speed |
| 3.125 kbps | 8 / 256 | 4/5 | 125 | 143dB | |
| 1.953 kbps | 8 / 256 | 4/8 | 125 | 143dB | |
| 1.343 kbps | 11 / 2048 | 4/8 | 500 | 145dB | |
| 1.099 kbps | 9 / 512 | 4/8 | 125 | 146dB | |
| 0.814 kbps | 10 / 1024 | 4/6 | 125 | 149dB | |
| 0.610 kbps | 10 / 1024 | 4/8 | 125 | 149dB | |
| 0.488 kbps | 11 / 2048 | 4/6 | 125 | 152dB | |
| 0.336 kbps | 11 / 2048 | 4/8 | 125 | 152dB | |
| 0.073 kbps | 12 / 4096 | 4/5 | 31 | 160dB | Twice the range and/or coverage of "Long Slow", low resliance to noise |
| 0.046 kbps | 12 / 4096 | 4/8 | 31 | 160dB | Twice the range and/or coverage of "Long Slow", high resliance to noise |
The link budget used by these calculations assumes a transmit power of 17dBm and an antenna with 0dB gain. Adjust your link budget assumptions based on your actual devices.
These channel settings may have not been tested. Use at your own discression. Share on https://meshtastic.discourse.group with your successes or failure.
Cryptography
The preshared key used by the devices can be modified.
- 0 = No crypto
- 1 = Default channel key
- 2 - 10 = The default channel key, except with 1 through 9 added to the last byte
Use of cryptography can also be modified. To disable cryptography (maybe useful if you have HAM radio license):
meshtastic --setchan psk 0