Modulation Modes: Difference between revisions
Add and update user documentation for Lua extensions and the catalog |
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The SimTX Transmitter supports the following modulation modes. The '''Auto''' bandwidth option fills the typical bandwidth for the selected mode; the bandwidth field accepts any value down to the mode's minimum. | The SimTX Transmitter supports the following modulation modes. The '''Auto''' bandwidth option fills the typical bandwidth for the selected mode; the bandwidth field accepts any value down to the mode's minimum. | ||
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| FT8 || Franke-Taylor FT8 || 50 Hz || 50 Hz || 20 to 80 Hz | | FT8 || Franke-Taylor FT8 || 50 Hz || 50 Hz || 20 to 80 Hz | ||
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== Choose a mode == | |||
Modulation is how the audio or data is carried. Set the receiver to the same kind of signal. | |||
* For the [[Getting Started|first audio-file example]], use '''AM Double Sideband Full Carrier''' and tick '''Auto''' bandwidth. This is ordinary AM. | |||
* For narrow voice signals, use '''USB''' or '''LSB'''. These are single-sideband (SSB) modes; the receiver must use the correct sideband. | |||
* For broadcast-style stereo from PipeWire Stereo, use '''WFM'''. It needs much more bandwidth than SSB. | |||
* Use '''IQ''' only when another program already generates the waveform. | |||
* Selecting '''FT8''' or '''WSPR''' does not compose a message. The source must already contain the encoded signal. | |||
The typical and minimum bandwidths below are reference values. Keep Auto enabled until there is a reason to select a different width. | |||
== Mode notes == | == Mode notes == | ||
Revision as of 21:22, 13 September 2026
The SimTX Transmitter supports the following modulation modes. The Auto bandwidth option fills the typical bandwidth for the selected mode; the bandwidth field accepts any value down to the mode's minimum.
| Mode | Full name | Typical bandwidth | Minimum bandwidth | Audio range |
|---|---|---|---|---|
| AM (full carrier) | Amplitude modulation, double sideband, full carrier | 10 kHz | 160 Hz | 80 to 4500 Hz |
| AM (suppressed carrier) | Double sideband, suppressed carrier | 6 kHz | 160 Hz | 100 to 2800 Hz |
| USB | Upper sideband | 2700 Hz | 300 Hz | 350 to 2700 Hz |
| LSB | Lower sideband | 2700 Hz | 300 Hz | 350 to 2700 Hz |
| CW | Continuous wave (Morse keying) | 150 Hz | 50 Hz | n/a |
| NFM | Narrowband FM | 12.5 kHz | 2.5 kHz | 200 to 3000 Hz |
| WFM | Wideband FM (broadcast) | 180 kHz | 50 kHz | 30 Hz to 15 kHz |
| IQ | External complex IQ input | 48 kHz | 100 Hz | n/a |
| WSPR | Weak Signal Propagation Reporter | 6 Hz | 6 Hz | 0.5 to 3 Hz |
| FT8 | Franke-Taylor FT8 | 50 Hz | 50 Hz | 20 to 80 Hz |
Choose a mode
Modulation is how the audio or data is carried. Set the receiver to the same kind of signal.
- For the first audio-file example, use AM Double Sideband Full Carrier and tick Auto bandwidth. This is ordinary AM.
- For narrow voice signals, use USB or LSB. These are single-sideband (SSB) modes; the receiver must use the correct sideband.
- For broadcast-style stereo from PipeWire Stereo, use WFM. It needs much more bandwidth than SSB.
- Use IQ only when another program already generates the waveform.
- Selecting FT8 or WSPR does not compose a message. The source must already contain the encoded signal.
The typical and minimum bandwidths below are reference values. Keep Auto enabled until there is a reason to select a different width.
Mode notes
- USB and LSB are suppressed-carrier modes. The carrier leak and opposite-sideband suppression settings in Advanced Transmitter Settings control how imperfect the suppression is. By convention LSB is used below 10 MHz and USB above, but SimTX does not enforce this.
- AM modes expose the AM modulation index setting. An index above 1.0 is overmodulation and produces audible distortion and splatter.
- CW exposes the key rise time setting. Very short rise times produce key clicks that widen the occupied bandwidth. CW is also the most sensitive mode: its narrow bandwidth lets it remain readable on paths where voice modes fail, see Propagation Basics.
- NFM and WFM are constant-envelope modes; they are less affected by amplifier compression but need considerably more signal at the receiver than SSB. WFM supports stereo when fed from the PipeWire Stereo source.
- IQ passes externally generated complex baseband (for example from GNU Radio) straight to the channel. Selecting the GNU Radio IQ source forces this mode.
- WSPR and FT8 provide narrow digital-mode signal paths. The selected transmission source must already contain the corresponding encoded audio signal.
Extension modes
Installed Lua modulation extensions appear in the same selector. An extension may produce IQ directly or produce audio for a selectable built-in RF mode. Its declared controls and media inputs appear below the standard modulation fields.
Field interactions
- The low-cut field is editable for USB, LSB, both AM modes, NFM and WFM.
- Opposite-sideband suppression applies to USB and LSB only.
- Carrier leak applies to USB, LSB and suppressed-carrier AM.
- AM index applies to the two AM modes.
- CW rise time applies to CW only.
- PipeWire Stereo forces WFM; GNU Radio IQ forces IQ.