Transmitter Interface

This page is a reference for the SimTX Transmitter application window. The window is split into a configuration form on the left and a live monitoring area on the right, with a status bar at the bottom.

Read the window in this order

The 0.3.6 interface with the first-transmission example. On a smaller screen, scroll the left pane to reach the antenna and Start TX.

1. Station: name and place the virtual station.
2. RF Signal: choose the radio frequency, output power, and modulation.
3. Transmission Source: choose the sound or data to send.
4. Antenna: match the antenna to that frequency.
5. Start TX: create a session, then select it in the list on the right.

The right-hand meters describe the selected session, or an estimate before transmission. A nonzero local estimate does not mean a transmission has started. The complete first-use sequence is in Getting Started.

Server selector

After signing in, select a server and use Connect to open the main window. Disconnect returns to this selector.

If the connection to the server drops while the application is running, the title area indicates that the client is reconnecting and retries every 3 seconds.

Station section

• Server row with a Disconnect button (returns to the server selector).
• Callsign: station identifier shown to the server and other users. Persisted between runs.
• Location: a clickable world map that fills the Lat and Lon fields. Coordinates can also be typed directly. Persisted between runs.

RF Signal section

• Frequency (Hz): carrier frequency. Default 4625000 (4625 kHz), chosen to match the default antenna, see Getting Started.
• Power (W): requested transmitter output power. Default 100.
• Radio Preset: selects a transmitter character, see Radio Presets. Selecting a preset overwrites the power field and all advanced settings.
• Modulation: the built-in or installed Lua modulation mode, see Modulation Modes and Lua extensions. Installed modes add their own controls and inputs below the standard fields.
• Bandwidth (Hz) with an Auto checkbox. Auto fills the typical bandwidth of the selected mode. Default 2700.
• Low-cut (Hz): audio low-frequency cutoff. Default 350. Editable only for modes where it applies.
• Show advanced transmitter settings: expands the fifteen fine-tuning fields, see Advanced Transmitter Settings.

Transmission Source section

• Source Type: see Transmission Sources.
• Audio Gain: input level, default 0.9.
• Microphone: device selector, visible only for the Microphone source.
• Tone (Hz): test tone frequency, default 1000. For the GNU Radio IQ source this field is relabelled IQ Port.
• Audio File row with Choose..., URL..., and Repeat. Local files can also be dragged onto the window (wav, mp3, aiff, aif, au). URL accepts HTTP and HTTPS audio streams. Repeat restarts a local file when it ends.

A hint line below the controls describes the currently selected source.

Antenna section

• Type: antenna selector, default EFHW + 49:1 unun. See Antenna System.
• Wire Length (m): main dimension of the antenna. The label adapts to the type (Circumference for the loop, Element Length for the vertical, Driven Element for the Yagis). A value of 0 selects the nominal type-specific template length; it does not guarantee low SWR. The EFHW template uses 32.5 m.
• Height (m): feedpoint or apex height above ground. Default 10.
• Azimuth (°): orientation, 0 is north. Disabled for the vertical, which is omnidirectional.
• Feedline Loss (dB): fixed loss between transmitter and antenna.
• Import NEC... and Use built-in: load or clear a custom antenna geometry, see NEC File Import.

Start row

• Start TX: starts a transmission session with the current configuration.
• Presets: applies installed presets, saves the current settings, or loads a .stxpreset file. A preset includes every field, the source selection, and any imported NEC deck.

Radio Deck

The right-hand panel shows six meters:

Meter	Unit	Meaning
FWD	W	Forward output power
REF	W	Reflected power returning from the antenna
SWR	:1	Standing wave ratio at the transmitter
ALC	dB	Automatic level control action
TEMP	°C	Power amplifier finals temperature
BUF	s	Audio buffer fill

Before transmission, the deck shows an estimate. During transmission, it shows the selected session’s measurements. If the amplifier overheats the header shows a PA OVERHEATED warning, see Power Amplifier Behaviour.

Active Sessions

A list of the operator's sessions with id, callsign, frequency, modulation, power, status, source, SWR, bandwidth, and server address. Listen to Own TX monitors the selected running signal as received by the server before propagation. Live Edit changes its frequency, power, bandwidth, low cut, final drive, PA headroom, and compression without starting a new session. Frequency changes take effect on Enter, while the other fields apply after a short pause. Auto Reconnect restarts a session after a connection error. Other buttons are Stop Selected, Stop All, and Clear Finished. Session states are described in Sessions and Queueing.

Footer controls

• Extensions: lists installed packages, runs tools, reports loading problems, and provides package creation and editing. See Lua extensions.
• Add-ons: enables, configures, and orders installed Lua audio processors.
• Catalog: browses, installs, and publishes shared extensions and presets. See Extension catalog.
• Theme: selects the system appearance or an installed Lua theme.