Advanced Transmitter Settings: Difference between revisions

Latest revision as of 20:06, 24 October 2026

Home · Start here · All guides · Solve a problem · Radio terms · Developer API

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.

@@ Line 1: / Line 1: @@
 {{Documentation navigation}}
-The advanced settings panel ('''Show advanced transmitter settings''' in the RF Signal section) exposes fifteen parameters that define the transmitter's imperfections. [[Radio Presets]] fill all of them at once; manual edits are possible afterwards.
+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 [[SimTX Guide/Stations#Radios|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 ==
+Start from a [[Radio Presets|radio model]] and change one value at a time while listening to your own transmission.
+{| class="wikitable"
+! 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 ==
 {| class="wikitable mw-collapsible mw-collapsed"
 ! Setting !! Default !! Range !! Effect
@@ Line 36: / Line 53: @@
 | CW rise (ms) || 5.0 || 0 to 50 || CW keying envelope rise time. Very short values cause key clicks.
 |}
-Other bounds: frequency must be positive, power must be at least 0 W, and the duty cycle used by the amplifier model runs from 0 to 1 with a default of 0.5.
-The suppression-style values (carrier leak, sideband suppression, hum level, TX noise, phase noise) are expressed as decibels below the wanted signal, so larger numbers always mean a cleaner transmitter.
 [[Category:SimTX]]
-These controls are optional for first use. Begin with a [[Radio Presets|radio preset]] and change one value at a time while listening to your own transmission.
-* '''Distorted audio:''' first check source Audio Gain. Then examine Final drive, Compressor, and PA headroom.
-* '''Frequency shifted from the dial:''' check Freq error.
-* '''Deliberately simulating an imperfect radio:''' use the hum, noise, leakage, and mode-specific controls.
-PA means power amplifier. Headroom is the margin before it saturates. A higher suppression value means less unwanted signal, not more. The full table retains every range and default.