Radio Layer¶

MeshCore's radio layer sits between the routing core and physical hardware. This page covers supported radio chips, LoRa parameter configuration, regional frequency presets, airtime calculation, and Channel Activity Detection.

Supported Radio Chips¶

MeshCore supports six radio chipsets via RadioLib wrapper classes:

Chip	Max TX Power	Notes
SX1262	22 dBm	TCXO, preferred for new designs
SX1276	20 dBm	Legacy LoRa chip, widely used
SX1268	22 dBm	Variant of SX1262
LR1110	22 dBm	Integrated GNSS (GPS)
LLCC68	22 dBm	Budget variant of SX1262
STM32WL	22 dBm	Integrated SoC (MCU + radio in one chip)

All chips connect to the MCU via SPI. Each chip has a corresponding wrapper in src/helpers/radiolib/ that adapts the RadioLib API to the MeshCore hardware abstraction.

The SX1262 is the recommended choice for new hardware designs: TCXO reference oscillator, good sensitivity, widely available.

LoRa Parameters¶

MeshCore uses four LoRa parameters to define the radio channel. All nodes on the same network must use identical parameters or they cannot decode each other's packets.

Parameter	Field	Typical Range	Notes
Frequency	`freq`	868–928 MHz	Region-dependent
Bandwidth	`bw`	62.5 / 125 / 250 kHz	Network-wide setting
Spreading Factor	`sf`	SF7–SF12	Affects range, data rate, airtime
Coding Rate	`cr`	⅘ to 4/8	Error correction overhead
TX Power	`tx_power_dbm`	−9 to +22 dBm	Per-node, does not need to match

Configure via CLI:

set radio <freq_MHz> <bw_kHz> <sf> <cr>
set txpow <dBm>

Regional Frequency Presets¶

Default parameters by region:

Region	Frequency	Bandwidth	SF	CR	Notes
EU	869.525 MHz	62.5 kHz	7–9	⅘	10% duty cycle sub-band
US / Canada	910.525 MHz	62.5 kHz	7	⅘
Australia / NZ	915.0 MHz	62.5 kHz	7–9	⅘	915–928 MHz ISM band
Switzerland	869.618 MHz	62.5 kHz	8	4/8

Australia/NZ note: The 915–928 MHz band has generous frequency hopping or wideband rules. MeshCore uses a single fixed frequency rather than frequency hopping, so it operates as a fixed narrowband system within this band. Check ACMA guidelines for your specific use case.

62.5 kHz Bandwidth and LoRaWAN Incompatibility¶

The dominant preset uses 62.5 kHz bandwidth. This is narrower than LoRaWAN gateway concentrators, which require ≥ 125 kHz. As a result, MeshCore networks are entirely independent of LoRaWAN infrastructure — they cannot share concentrators, gateways, or network servers with LoRaWAN devices.

This is not a bug: it is a deliberate choice to use the narrowest practical bandwidth, which provides: - Higher effective sensitivity (narrower noise bandwidth) - More frequency diversity (more channels fit in the same spectrum) - Independence from LoRaWAN congestion

Spreading Factor Trade-offs¶

Spreading Factor controls the balance between range, data rate, and airtime:

SF	Data Rate	Airtime	Sensitivity	Max Range
SF7	Fastest	Shortest	−123 dBm	Shortest
SF8			−126 dBm
SF9			−129 dBm
SF10			−132 dBm
SF11			−134.5 dBm
SF12	Slowest	Longest	−137 dBm	Longest

Minimum decodable SNR (from RadioLib calibration):

SF	Min SNR
SF7	−7.5 dB
SF8	−10.0 dB
SF9	−12.5 dB
SF10	−15.0 dB
SF11	−17.5 dB
SF12	−20.0 dB

For community mesh networks, SF9 at 62.5 kHz is a common balanced choice — longer range than SF7 without the severe airtime penalty of SF12.

Important: Changing SF changes airtime significantly. A message that takes 200 ms at SF7 may take 1600 ms at SF9 on 62.5 kHz. This directly affects duty cycle limits and network throughput.

Airtime Estimation¶

The firmware uses RadioLib's built-in time-on-air calculator:

airtime_ms = radio.getTimeOnAir(packet_length_bytes) / 1000

The Dispatcher queries this before queuing transmissions to enforce the airtime budget.

Example Airtimes (approximate, 62.5 kHz BW)¶

SF	50-byte packet	100-byte packet	200-byte packet
SF7	~85 ms	~155 ms	~290 ms
SF9	~340 ms	~625 ms	~1150 ms
SF12	~2700 ms	~5000 ms	~9200 ms

These are rough estimates; actual values depend on coding rate, preamble length, and header mode.

Duty Cycle and Airtime Budget¶

The Dispatcher enforces an airtime budget to stay within duty cycle limits:

airtime_budget_factor = 2.0
duty_cycle = 100 / (factor + 1) = 33.3%

The radio must be silent for at least 2× the last transmission duration before the next transmission fires.

For stricter regional limits (e.g., EU 869.525 MHz at 10% max):

set af 9.0   (airtime factor = 9.0 → 10% duty cycle)

Formula: duty_cycle = 100 / (af + 1)

`af` value	Effective duty cycle
1.0	50%
4.0	20%
9.0	10% (EU legal limit for this sub-band)
19.0	5%

Channel Activity Detection (CAD)¶

Before every transmission, the Dispatcher performs LoRa Channel Activity Detection to check if the channel is already in use.

Timing constants:

Constant	Value	Description
`CAD_FAIL_MAX_DURATION`	4000 ms	If channel stays busy this long, declare CAD timeout error
`STARTRX_TIMEOUT`	8000 ms	Watchdog for radio stuck in TX
`NOISE_FLOOR_CALIB_INTERVAL`	2000 ms	Interval between RSSI noise floor samples

Noise Floor Calibration¶

The firmware continuously samples RSSI at 2-second intervals. 64 consecutive samples below a threshold are used to compute the noise floor baseline, clamped at a minimum of −120 dBm.

Elevated noise floor readings indicate: - Local RF interference (WiFi on 900 MHz where applicable, industrial equipment) - Other LoRa networks on the same or adjacent frequency - Hardware issues (faulty antenna, damaged RF path)

SNR Storage Format¶

Throughout the firmware, SNR is stored as int8_t in quarter-dB units:

stored_value = SNR_float * 4
SNR_float    = stored_value / 4.0

This allows -32.0 dB to +31.75 dB range in a single signed byte. Always remember to divide by 4 when reading raw stats values.

Receive Sensitivity and Link Budget¶

Approximate receive sensitivity (SX1262, BW 62.5 kHz):

SF	Sensitivity
SF7	−123 dBm
SF9	−129 dBm
SF12	−137 dBm

Example link budget (SX1262, SF9, 62.5 kHz):

TX power:          +22 dBm  (SX1262 max)
TX antenna gain:    +3 dBi  (simple vertical)
Cable/connector:    −1 dB
Free space path:  −140 dB   (≈30 km at 915 MHz, with terrain loss)
RX antenna gain:   +3 dBi
RX sensitivity:  −129 dBm

Available margin:  22 + 3 - 1 - 140 + 3 - (-129) = +16 dB

A 16 dB margin is comfortable. Real-world performance depends heavily on terrain, obstructions, and antenna installation quality.