mTX Documentation

Very rudimentary documentation of few things.

RSSI

The topic of RSSI is complicated, as there are many different sources and different units/scalings in the game.

Units/scaling

dBm: real units so to say, rssi is negative (except in super close range)
negated dBm: like dBm but with opposite sign, rssi is positive (except in super close range)
mavlink units: device-dependent units/scale, values 0 .. 254, 255 = invalid/unknown
ArduPilot scaling: values 0 .. 255
percentage: 0 .. 100%, the scaling or reference points can vary
ArduPilot CRSF scaling: converts dBm to mavlink units using the formula (1 - (|rssi| - 50)/70) * 255, 50/-50 dBm corresponds to 255, 120/-120 dBm corresponds to 0

Sources

MAVLink
- MAVLink message RADIO_STATUS (#109)
  - uint8_t rssi: mavlink units, rssi for reception on Tx module
  - uint8_t remrssi: mavlink units, rssi for reception on Rx module
  - uint8_t noise: noise on Tx module side
  - uint8_t remnoise: noise on Rx module side
- MAVLink message RC_CHANNELS (#65)
  - uint8_t rssi: mavlink units
- MAVLink message RC_CHANNELS_RAW (#35)
  - uint8_t rssi: mavlink units
mBridge
- rssi in negative dBm, is converted to mavlink units using AP CRSF formula
CRSF
- none yet

mTx MavSdk Lua Functions

getRadioRssiRaw(): rssi in mavlink units. Selects from the various sources according in this priority: mBridge, RADIO_STATUS, RC_CHANNELS, RC_CHANNELS_RAW
getRadioRssiScaled(): same as getRadioRssiRaw() but if the parameter mavlinkRssiScale is non zero it is scaled into percentage (0% .. 100%) using that scale factor
getRadioRssi(): if the parameter mavlinkRssiScale is non zero return the value of getRadioRssiScaled() else that of getRadioRssiRaw(). Should normally be used

LQ

Sources

MAVLink: none
mBridge:
- rssi in negative dBm, is converted to mavlink units using AP CRSF formula
CRSF: none

mTx MavSdk Lua Functions

getRadioLQ():