SimTX Transmitter

This page describes the legacy Java client. The SimTX app is the recommended client; start with Getting Started and the SimTX Guide.

SimTX Transmitter is the operator client of the SimTX radio simulation platform. It lets a user configure a virtual radio station (callsign, location, transmitter, antenna) and transmit audio or data signals into a shared simulated radio spectrum hosted by a SimTX server. Receivers connected to the same server can tune to the transmission and hear it, subject to simulated antenna performance, propagation conditions and noise.

Start with one task

New to SimTX? Follow Getting Started for downloading, account sign-in, and an audio-file transmission. No knowledge of antenna formulas or Lua is required.

The basic path is audio source → transmitter → simulated radio path → receiver. The transmitter app controls the station. A separate receiver lets a listener choose a frequency and hear the result. Both use the same server.

For a control you cannot identify, use Transmitter Interface. For a term you do not recognize, use Radio terms.

All transmissions are simulated; no physical radio equipment is required.

Overview

A transmitter session works as follows:

1. The operator starts the application and signs in to a SimTX account, then selects an official server.
2. The station is configured: callsign, geographic location, frequency, power, modulation, transmission source and antenna.
3. The operator presses Start TX. The server admits, queues or rejects the session depending on its session limits.
4. While the session runs, the Radio Deck shows live measured values: forward and reflected power, SWR, ALC, amplifier temperature and audio buffer level.
5. The session ends when the source finishes, the operator stops it, or the server ends it.

Main topics

• Getting Started: installation, connecting to a server, first transmission
• Transmitter Interface: reference for every control in the application window
• Modulation Modes: supported modes and their bandwidths
• Transmission Sources: audio files and URLs, microphone, white noise, PipeWire, GNU Radio IQ
• Lua extensions: modulation modes, audio add-ons, tools, themes, and libraries
• Extension catalog: shared extensions and complete station presets
• Radio Presets: built-in transmitter characteristics, from clean lab exciters to overdriven CB rigs
• Advanced Transmitter Settings: the fifteen fine-tuning parameters
• Station Configuration: callsign, location and saving station presets
• Antenna System: how antennas behave and are configured, with a page per antenna type
• Antenna Calculations: resonant lengths, SWR, gain and loss arithmetic
• SWR and Transmitter Protection: what happens when the antenna is mismatched
• Power Amplifier Behaviour: heating, power foldback and permanent damage
• Sessions and Queueing: admission, queue positions, rejections and kicks
• Propagation Basics: what determines whether a signal is heard at a distance

What SimTX simulates

From the operator's point of view the simulation covers:

• Transmitter imperfections: compression, distortion, carrier leakage, hum, phase noise and more, selectable through Radio Presets or tuned individually.
• Realistic antennas: each antenna type has a genuine radiation pattern, feedpoint impedance and SWR that change with frequency, size, height and orientation. Custom antennas can be imported as NEC decks, see NEC File Import.
• Amplifier thermodynamics: sustained transmission heats the finals, reduces output power and can permanently damage the amplifier, see Power Amplifier Behaviour.
• Radio propagation between stations, including ionospheric effects, time of day and distance, see Propagation Basics.