sdrangel/plugins/channeltx/modnfm/readme.md

<h1>NFM modulator plugin</h1>

<h2>Introduction</h2>

This plugin can be used to generate a narrowband frequency modulated signal. "Narrowband" means that the bandwidth can vary from 1 to 40 kHz.

<h2>Interface</h2>

![NFM Modulator plugin GUI](../../../doc/img/NFMMod_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: Channel mute</h3>

Use this button to toggle mute for this channel.

<h3>5: RF bandwidth</h3>

This is the bandwidth in kHz of the channel signal filtered after modulation. It can be set in discrete values: 3, 4, 5, 6.25, 8.33, 10, 12.5, 15, 20, 25 and 40 kHz

<h3>6: Audio frequency bandwidth</h3>

This is the bandwidth in khz of the modulating signal filtered before modulation. It can be set in kHz steps from 1 to 20 kHz 

<h3>7: Frequency deviation</h3>

Adjusts the frequency deviation in 0.1 kHz steps from 0 to 25 kHz

<h3>8: 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.

<h3>9: 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>10: Input source control</h3>

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

<h4>10.1: Tone input select</h4>

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

<h4>10.2: Morse keyer input select</h4>

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

<h4>10.3: Tone frequency (kHz)</h4>

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

<h4>10.4: Audio input select</h4>

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

<h3>11: CTCSS switch</h3>

Checkbox to switch on the CTCSS sub-audio tone 

<h3>12: CTSS tone frequency</h3>

Select the CTCSS sub-audio tone in Hz among these values: 67.0,  71.9,  74.4,  77.0,  79.7,  82.5,  85.4,  88.5,  91.5,  94.8, 97.4, 100.0, 103.5, 107.2, 110.9, 114.8, 118.8, 123.0, 127.3, 131.8, 136.5, 141.3, 146.2, 151.4, 156.7, 162.2, 167.9, 173.8, 179.9, 186.2, 192.8 and 203.5 Hz

<h3>14: CW (Morse) text</h3>

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

<h3>15: Clear CW text</h3>

Clears the CW (Morse) text

<h3>16: Morse keyer controls</h3>

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

<h4>16.1: 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>16.2: Dots keying</h4>

Switch this button to send dots continuously

<h4>16.3: Dashes keying</h4>

Switch this button to send dashes continuously

<h4>16.4: Text keying</h4>

Switch this button to send the text typed into the text box (14)

<h4>16.5: Text auto repeat</h4>

Switch this button to auto repeat the text keying

<h4>12.6: Text play/stop</h4>

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

<h3>17: Audio file path</h3>

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

<h3>18: Audio file play controls</h3>

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

<h4>18.1: 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>18.2: Audio file loop</h4>

Audio replay file at the end

<h4>18.3: Play/pause file play</h4>

Toggle play/pause file play. When paused the slider below (17) can be used to randomly set the position in the file when re-starting.

<h3>19: Play file current position</h3>

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

<h3>20: Play file length</h3>

This is the audio file play length in time units

<h3>21: 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 18.3)