SimTX API v24/Packets/TxTelemetry

TxTelemetry

Packet ID	7(0x07)
Direction	Server → client
Session	Transmitter
Body size	81 bytes
Permission	None
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TxTelemetry reports the state of a transmitter while it is on air: power at each point of the chain, standing-wave ratio, amplifier compression and temperature, and the server's playout buffer. The server sends it about every 50 ms from TxAccept until the session ends. These are the values behind the meters of the official transmitter.

Layout

Field	Type	Description
packetId	u8	Always 7.
sequence	i64	Increments with each telemetry packet.
serverTimeMillis	i64	Server wall-clock time, Unix milliseconds.
actualFrequencyHz	f32	Frequency on air, including any frequency offset.
requestedPowerWatts	f32	Power requested, after the account limit.
forwardPowerWatts	f32	Power leaving the amplifier toward the antenna.
deliveredPowerWatts	f32	Power actually accepted by the antenna.
reflectedPowerWatts	f32	Power reflected back by the mismatch.
vswr	f32	Voltage standing-wave ratio at the feed point.
mismatchLossDb	f32	Loss due to the mismatch, in dB.
transformerLossDb	f32	Loss in the matching transformer, in dB.
foldbackLossDb	f32	Power reduction by SWR protection, in dB.
alcDb	f32	Automatic level control reduction, in dB.
bufferSeconds	f32	Samples waiting in the server's playout buffer, in seconds.
finalsTemperatureC	f32	Temperature of the final amplifier, °C.
thermalFoldbackDb	f32	Power reduction by thermal protection, in dB.
paCompressionDb	f32	Amplifier gain compression, in dB.
paHeatWatts	f32	Heat dissipated in the amplifier, in watts.
paEfficiencyPercent	f32	Amplifier efficiency, percent.
paThermalFaultActive	bool	True while the amplifier is in thermal fault.

Usage

• Pacing: bufferSeconds is the most useful field for a streaming client. It should stay above zero (otherwise listeners hear gaps) and below about two seconds (otherwise latency grows and input may be discarded).
• Antenna match: a high vswr with large reflectedPowerWatts and foldbackLossDb means the antenna is not resonant on the frequency. See SWR and Transmitter Protection.
• Heat: finalsTemperatureC, thermalFoldbackDb and paThermalFaultActive follow the amplifier model described in Power Amplifier Behaviour.
• Telemetry is coalesced. A slow reader gets the most recent values rather than a backlog; sequence may skip.
• The client must keep reading. A client that does not read for 5 seconds is disconnected.

In Python: struct.unpack(">qq16f?", body).

See also

• SWR and Transmitter Protection
• Power Amplifier Behaviour