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
- Under Station, choose the station in Transmit from, then its Antenna and Radio.
- Under RF signal, set Frequency, Power (W) and Modulation.
- Under Source, choose what to send.
- Press Start TX.
If something is missing, a message beside Start TX says what, with a button that fixes it. See Troubleshooting.
Station
| 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
| 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
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
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.
- Open Settings, Push-to-talk.
- Choose the Mode: Toggle switches with each press, Hold to talk transmits while the button is held.
- 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.