sdrangel/plugins/channeltx/modssb/readme.md

<h1>SSB modulator plugin</h1>

<h2>Introduction</h2>

This plugin can be used to generate a single sideband or double sidebands modulated signal.

<h2>Interface</h2>

![SSB Modulator plugin GUI](../../../doc/img/SSBMod_plugin.png)

<h3>1: Frequency shift from center frequency of reception direction</h3>

The "+/-" button on the left side of the dial toggles between positive and negative shift.

<h3>2: Frequency shift from center frequency of reception value</h3>

Use the wheels to adjust the frequency shift in Hz from the center frequency of reception. Left click on a digit sets the cursor position at this digit. Right click on a digit sets all digits on the right to zero. This effectively floors value at the digit position.

<h3>3: Channel power</h3>

Average total power in dB relative to a +/- 1.0 amplitude signal generated in the pass band.

<h3>4: Binaural mode</h3>

Use this button to toggle between monaural and binaural mode. Monaural is classical single sideband or double sidebands modulation. In binaural mode I and Q samples are taken from the left and right stereo channels (or reversed).

When in monaural mode the icon shows a single loudspeaker and when in binaural mode it shows a pair of loudspeakers.

<h3>5: Reverse left and right channels in binaural mode</h3>

Effective only in binaural mode: reverses left and right audio channels so that the left is connected to Q and the right to the I complex signal channel. 

<h3>6: SSB/DSB</h3>

Selects between SSB and DSB operation. When in SSB mode the icon shows a single sideband spectrum (USB side). When in DSB mode the icon shows a double sideband spectrum. 

<h3>7: Spectrum display frequency span</h3>

The transmitted signal in the sideband (SSB) or sidebands (DSB) is further decimated by a power of two before being applied to the channel spectrum display. Thus the frequency span of the spectrum display is the audio sample rate (48 kHz) divided by the decimation factor.

<h3>8: Signal bandwidth</h3>

The modulating signal is bandpass filtered (SSB) or lowpass filtered (DSB) before being multiplied by the local oscillator NCO. This is the upper limit of the filter in absolute value.

When this limit is positive the signal is transmitted in the upper sideband (USB). When this limit is negative the signal is transmitted in the lower sideband (LSB).

<h3>9: Filter low frequency cutoff</h3>

In SSB mode this is the lower limit in absolute value of the modulating signal bandpass filter

<h3>10: Volume</h3>

This is the volume of the audio signal from 0.0 (mute) to 2.0 (maximum). It can be varied continuously in 0.1 steps using the dial button. The Loudspeaker button is the audio mute toggle.

<h3>11: Level meter in %</h3>

  - top bar (beige): average value
  - bottom bar (brown): instantaneous peak value
  - tip vertical bar (bright red): peak hold value

You should aim at keepimg the peak value below 100% using the volume control

<h3>12: Input source control</h3>

![Modulator input source control GUI](../../../doc/img/ModControls.png)

<h4>12.1: Tone input select</h4>

Switches to the tone input. You must switch it off to make other inputs available.

<h4>12.2: Morse keyer input select</h4>

Switches to the Morse keyer input. You must switch it off to make other inputs available.

<h4>12.3: Tone frequency (kHz)</h4>

Adjusts the tone frequency from 0.1 to 2.5 kHz in 0.01 kHz steps

<h4>12.4: Audio input select</h4>

Switches to the audio input. You must switch it off to make other inputs available.

<h3>13: CW (Morse) text</h3>

Enter the text to be keyed when Morse input is active and in text mode

<h3>14: Clear CW text</h3>

Clears the CW (Morse) text

<h3>15: Morse keyer controls</h3>

![Morse keyer control GUI](../../../doc/img/ModCWControls.png)

<h4>15.1: CW keying speed</h4>

Sets the CW speed in Words Per Minute (WPM). This is based on the word "PARIS" sent 5 times. For 5 WPM the dot length is 240 ms. In other terms the dot length is calculated as 1.2 / WPM seconds. The dot length is used as the base to compute other timings:

  - Element (dot or dash) silence separator: 1 dot length
  - Dash: 3 dot lengths
  - Character silence separator: 3 dot lengths
  - Word silence separator: 7 dot lengths
  
<h4>15.2: Dots keying</h4>

Switch this button to send dots continuously

<h4>15.3: Dashes keying</h4>

Switch this button to send dashes continuously

<h4>15.4: Text keying</h4>

Switch this button to send the text typed into the text box (13)

<h4>15.5: Text auto repeat</h4>

Switch this button to auto repeat the text keying

<h4>15.6: Text play/stop</h4>

Use this button to stop sending text. When resuming keying restarts at the start of text

<h3>16: Audio file path</h3>

The path to the selected audio file to be played or dots if unselected

<h3>17: Audio file play controls</h3>

![Modulator audio file play control GUI](../../../doc/img/ModFileControls.png)

<h4>17.1: Audio file select</h4>

Opens a file dialog to select the audio file to be played. It must be mono 48 kHz 16LE raw format.

<h4>17.2: Audio file loop</h4>

Audio replay file at the end

<h4>17.3: Play/pause file play</h4>

Toggle play/pause file play. When paused the slider below (20) can be used to randomly set the position in the file when re-starting.

<h3>18: Play file current position</h3>

This is the current audio file play position in time units relative to the start

<h3>19: Play file length</h3>

This is the audio file play length in time units

<h3>20: Play file position slider</h3>

This slider can be used to randomly set the currennt position in the file when file play is in pause state (button 17.3)

<h3>21: Channel spectrum display</h3>

This is the channel spectrum display. Controls at the bottom of the panel are the same as with the central spectrum display.