SimTX Guide/Transmitting

The Transmit tab puts a signal on the air from one of your stations. The setup is on the left; the Radio deck and the Sessions list are on the right.

Transmit a signal

1. Under Station, choose the station in Transmit from, then its Antenna and Radio.
2. Under RF signal, set Frequency, Power (W) and Modulation.
3. Under Source, choose what to send.
4. Press Start TX.

If something is missing, a message beside Start TX says what, with a button that fixes it. See Troubleshooting.

Station

The Station section with a rotator antenna chosen, showing the Rotator dial and the SWR around the frequency.

Control	What it does
Transmit from	The station the transmission runs from. It sets your callsign and location. Create a station appears if you have none.
Antenna, Radio	The station's antenna and radio to use. The first radio is the default.
Edit station	Opens the station editor.
Track a satellite	Corrects Doppler for a satellite, and points a rotator at it. See Rotators and tracking.
Rotator	Turns an antenna on a rotator. Shown only for rotator antennas.
SWR around your frequency	The antenna's SWR near the transmit frequency.

Stations covers creating stations, antennas and radios.

RF signal

Control	What it does
Frequency	The carrier or dial frequency. The unit menu switches between Hz, kHz and MHz.
Power (W)	Transmitter power. The label shows up to the radio's power cap.
Modulation	The mode, for example AM, SSB, FM or a data mode. See Modulation Modes.
Bandwidth (Hz)	The transmitted bandwidth. Auto uses the usual bandwidth of the mode.
Low-cut (Hz)	Removes audio below this frequency.
WFM input	For wide FM: MPX composite (channel 1), which needs a source at 192 kHz or more, or Mono baseband with a Pre-emphasis of none, 50 µs or 75 µs.
Transmitter imperfections	Final drive, compressor, frequency error and AM index for this transmission. They start from the radio's values. See Advanced Transmitter Settings.

The line Wire rate shows the audio sample rate sent to the server. Modes from an extension show their own controls here.

Source

The Source menu with the five source types.

Source	Sends	Settings
Audio file	An audio file or stream.	File or URL, Choose…, Loop playback
Input device	A microphone or other audio input.	Input device, Capture rate (Hz)
White noise	A test signal generated by the server.	Tone (Hz)
PipeWire	Audio from the PipeWire graph on Linux.	Capture rate (Hz)
GNU Radio IQ	Complex baseband from GNU Radio, for modulation IQ.	IQ port (127.0.0.1); set the GNU Radio sink to the rate shown.

Audio gain sets the level of the source. Transmission Sources has more on each source.

Presets

Presets at the top saves and loads complete transmit setups.

• To save, type a Preset name and press Save. A preset with the same name is replaced after you confirm.
• To load, choose a saved preset from the list.
• Load from file… and Save to file… use a preset file anywhere on disk. Open presets folder shows where saved presets are kept.

Presets from other users are in the Catalog tab; see Catalog and add-ons.

Radio deck

Adjust while on air, opened under the Radio deck meters.

The Radio deck for a running USB session, with its meters and the Pause and Stop buttons.

Select a session in the Sessions list to show it in the radio deck.

Meter	Shows
FWD/W	Power leaving the transmitter.
REF/W	Power reflected by the antenna.
SWR/:1	How well the antenna matches. The higher it is, the less power reaches the antenna. See SWR and Transmitter Protection.
ALC/dB	How much the level control is reducing the signal.
TEMP/C	Temperature of the final amplifier. See Power Amplifier Behaviour.
BUF/s	Audio waiting at the server. Near zero, listeners hear gaps.
DEV/kHz	FM deviation, with a reference tick.
MOD/%	AM modulation depth.
DRV/%	IQ drive level.

• Pause silences the session without ending it; Resume continues.
• Stop ends the session.
• Adjust while on air changes Frequency, Power (W), Bandwidth (Hz), Final drive (dB), PA headroom (dB), Compressor (dB) and Audio gain without stopping. Type a value and press Enter.
• Listen to own TX plays your signal as transmitted, before propagation. Stop listening ends it.

Sessions

The Sessions list with a running, a paused, a queued and a finished session.

Each Start TX adds a session to the list, with its label, number, state and frequency. Stop all ends every session after you confirm. Clear finished removes ended sessions.

State	Meaning
Starting	Connecting to the server.
Queued	Every transmitter slot on the server is taken. It starts by itself when one is free.
Running	On the air.
Paused	On the air but silent.
Stopped	Ended by you.
Finished	The audio file ended.
Failed	Ended by an error. The message says why.
Kicked	Ended by the server, for example by a moderator, or because the station was deleted or its satellite reentered. The message gives the reason.

Push-to-talk

Push-to-talk pauses and resumes your transmission with a key or mouse button while the app window is in front.

1. Open Settings, Push-to-talk.
2. Choose the Mode: Toggle switches with each press, Hold to talk transmits while the button is held.
3. Press Bind next to Key or Mouse button, then press the key or click the button.

If nothing is on the air, pressing push-to-talk starts a session with the current setup.

Keyboard

Action	Windows and Linux	macOS
Start TX	Ctrl+Enter	⌘↵
Set TX frequency	Ctrl+Shift+F	⌘⇧F
Set TX power	Ctrl+Shift+W	⌘⇧W
Set modulation	Ctrl+Shift+M	⌘⇧M
Listen to own TX	Ctrl+Shift+L	⌘⇧L

In the command palette (Ctrl+K or ⌘K), typing a frequency such as 14.230 or a power such as 100 W offers to set it. See Settings and shortcuts.