Advanced Transmitter Settings
Fifteen parameters define a transmitter's imperfections. In the SimTX desktop app they are set in two places:
- On a station's radio. Each radio stores all fifteen under Transmitter imperfections in the station editor. Choosing a model under Based on fills them. See Radios.
- For one transmission. In the Transmit tab, Transmitter imperfections in the RF signal section adjusts four of them: Final drive, Compressor, Freq error and AM index. They start from the station radio's values. The other eleven come from the radio.
Which setting to change[edit | edit source]
Start from a radio model and change one value at a time while listening to your own transmission.
| Problem | Settings |
|---|---|
| Distorted audio | The source's Audio gain first, then Final drive, Compressor and PA headroom. |
| Signal off the dial frequency | Freq error. |
| An imperfect radio on purpose | Hum, noise, leakage and the mode-specific settings. |
PA means power amplifier. Headroom is the margin before it saturates. Carrier leak, sideband suppression, hum level, TX noise and phase noise are in decibels below the wanted signal: a larger number means a cleaner transmitter.
Parameter reference[edit | edit source]
| Setting | Default | Range | Effect |
|---|---|---|---|
| Final drive (dB) | 0.0 | -40 to 40 | Extra drive into the power amplifier. Positive values push the amplifier toward compression and distortion. |
| PA headroom (dB) | 12.0 | 0.1 to 40 | How far below amplifier saturation the nominal signal sits. Small headroom means the signal clips early. |
| Compressor (dB) | 1.5 | 0 to 30 | Audio compression before modulation. Raises average loudness at the cost of naturalness. |
| PA softness | 2.8 | 0.5 to 10 | Shape of the amplifier limiting curve. Low values clip abruptly (harsh distortion), high values limit gently. |
| AM/PM (deg) | 6.0 | 0 to 45 | Phase shift that accompanies amplitude compression. Adds splatter and roughness when the amplifier is driven hard. |
| Carrier leak (dB) | 60.0 | 0 to 120 | Suppression of the residual carrier in suppressed-carrier modes. Higher is cleaner. |
| Sideband sup. (dB) | 60.0 | 0 to 120 | Suppression of the unwanted sideband in SSB. Higher is cleaner. |
| Freq error (Hz) | 0.0 | -10000 to 10000 | Static frequency offset of the transmitter oscillator. |
| Hum level (dB) | 120.0 | 0 to 120 | Mains hum suppression; 120 means no audible hum. Lower values add hum at the hum frequency. |
| Hum freq (Hz) | 0.0 | 0 to 400 | Mains hum fundamental (typically 50 or 100, or 60 or 120). Zero disables. |
| AM index | 0.85 | 0 to 1.2 | AM modulation depth. Above 1.0 is overmodulation with distortion and splatter. |
| PA sag (dB) | 0.0 | 0 to 30 | Supply voltage sag under load; produces a power dip on voice peaks and key-down. |
| TX noise (dB) | 120.0 | 0 to 160 | Broadband transmitted noise floor suppression. Higher is cleaner. |
| Phase noise (dB) | 120.0 | 0 to 160 | Oscillator phase noise suppression. Higher is cleaner; low values smear the signal spectrally. |
| CW rise (ms) | 5.0 | 0 to 50 | CW keying envelope rise time. Very short values cause key clicks. |