SimTX API/Packets/TxTelemetry

TxTelemetry

Frame	ServerFrame, field 17
Member	tx_telemetry
Direction	Server → client
Session	Transmitter
Roles	ROLE_TX_AUDIO, ROLE_TX_GENERATED.
Permission	None
Answered by
Answers
Defined in	session.proto

TxTelemetry reports the state of a transmitter 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.

Definition

message TxTelemetry {
  int64 sequence = 1;
  int64 server_time_ms = 2;
  double actual_frequency_hz = 3;
  float requested_power_watts = 4;
  float forward_power_watts = 5;
  float delivered_power_watts = 6;
  float reflected_power_watts = 7;
  float vswr = 8;
  float mismatch_loss_db = 9;
  float transformer_loss_db = 10;
  float foldback_loss_db = 11;
  float alc_db = 12;
  float buffer_seconds = 13;
  float finals_temperature_c = 14;
  float thermal_foldback_db = 15;
  float pa_compression_db = 16;
  float pa_heat_watts = 17;
  float pa_efficiency_percent = 18;
  bool pa_thermal_fault_active = 19;
}

Fields

#	Field	Type	Description
1	sequence	int64	Increments with each telemetry frame. Telemetry is coalesced, so values may be skipped.
2	server_time_ms	int64	Server wall clock, Unix ms.
3	actual_frequency_hz	double	Frequency on air in Hz: the requested frequency plus the frequency offset.
4	requested_power_watts	float	Power requested, after the PA cap.
5	forward_power_watts	float	Power leaving the amplifier towards the antenna.
6	delivered_power_watts	float	Power accepted by the antenna.
7	reflected_power_watts	float	Power reflected by the mismatch.
8	vswr	float	Voltage standing-wave ratio at the feed point.
9	mismatch_loss_db	float	Loss due to the mismatch, dB.
10	transformer_loss_db	float	Loss in the matching transformer, dB.
11	foldback_loss_db	float	Power reduction by SWR protection, dB.
12	alc_db	float	Automatic level control reduction, dB.
13	buffer_seconds	float	Samples waiting in the server's playout buffer, seconds.
14	finals_temperature_c	float	Temperature of the final amplifier, °C.
15	thermal_foldback_db	float	Power reduction by thermal protection, dB.
16	pa_compression_db	float	Amplifier gain compression, dB.
17	pa_heat_watts	float	Heat dissipated in the amplifier, W.
18	pa_efficiency_percent	float	Amplifier efficiency, percent.
19	pa_thermal_fault_active	bool	True while the amplifier is in thermal fault.

Usage

• Pacing: buffer_seconds is the most useful field for a streaming client. Keep it 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 reflected_power_watts and foldback_loss_db means the antenna is not resonant on the frequency. See SWR and Transmitter Protection.
• Heat: finals_temperature_c, thermal_foldback_db and pa_thermal_fault_active follow the amplifier model in Power Amplifier Behaviour.
• Telemetry is coalesced. A slow reader gets the most recent values rather than a backlog; sequence may skip.
• Keep reading. A client that does not read for 5 seconds is disconnected.

Example

Complete frames, including the varint length prefix.

tx_telemetry (server to client, 90 bytes):

59                            frame length 89
8A 01 56                      tx_telemetry (TxTelemetry), 86 bytes
  08 2A                       sequence = 42
  10 FA 95 83 B9 97 34        server_time_ms = 1793000000250
  19 00 00 00 00 34 FC 5A 41  actual_frequency_hz = 7074000.0
  25 00 00 C8 42              requested_power_watts = 100
  2D 00 00 C4 42              forward_power_watts = 98
  35 00 00 C1 42              delivered_power_watts = 96.5
  3D 00 00 C0 3F              reflected_power_watts = 1.5
  45 66 66 A6 3F              vswr = 1.3
  4D 29 5C 8F 3D              mismatch_loss_db = 0.07
  55 CD CC 4C 3E              transformer_loss_db = 0.2
  65 00 00 80 BF              alc_db = -1
  6D 00 00 80 3E              buffer_seconds = 0.25
  75 00 00 34 42              finals_temperature_c = 45
  85 01 9A 99 99 3F           pa_compression_db = 1.2
  8D 01 00 00 F0 41           pa_heat_watts = 30
  95 01 00 00 7A 42           pa_efficiency_percent = 62.5

See also

• SWR and Transmitter Protection
• Power Amplifier Behaviour